Showing 1–34 of 34 results for author: Hertz, E

Concept of a Double Tilted Rowland Spectrograph for X-rays

Authors: Hans Moritz Günther, Casey T. DeRoo, Ralf K. Heilmann, Edward Hertz

Abstract: High-resolution spectroscopy in soft X-rays ($<2$ keV) requires diffractive elements to resolve any astrophysically relevant diagnostics, such as closely spaced lines, weak absorption lines, or line profiles. The Rowland torus geometry describes how gratings and detectors need to be positioned to optimize the spectral resolving power. We describe how an on-axis Rowland geometry can be tilted to ac… ▽ More High-resolution spectroscopy in soft X-rays ($<2$ keV) requires diffractive elements to resolve any astrophysically relevant diagnostics, such as closely spaced lines, weak absorption lines, or line profiles. The Rowland torus geometry describes how gratings and detectors need to be positioned to optimize the spectral resolving power. We describe how an on-axis Rowland geometry can be tilted to accommodate blazed gratings. In this geometry, two channels with separate optical axes can share the same detectors (double tilted Rowland spectrograph, DTRS). Small offsets between the channels can mitigate the effect of chip gaps and reduce the alignment requirements during the construction of the instrument. The DTRS concept is especially useful for sub-apertured mirrors, because it allows an effective use of space in the entrance aperture of a spacecraft. One mission that applies this concept is the Arcus Probe. △ Less

Submitted 20 August, 2024; originally announced August 2024.

Comments: Accepted by ApJ, 13 pages, 9 figures. Interactive figures are not available on arxiv, but will be hosted by ApJ

Transmission grating arrays for the X-ray spectrometer on Arcus Probe

Authors: Ralf K. Heilmann, Alexander R. Bruccoleri, James A. Gregory, Eric M. Gullikson, Hans Moritz Günther, Edward Hertz, Renee D. Lambert, Douglas J. Young, Mark L. Schattenburg

Abstract: The Arcus Probe mission concept has been submitted as an Astrophysics Probe Explorer candidate. It features two co-aligned high-resolution grating spectrometers: one for the soft x-ray band and one for the far UV. Together, these instruments can provide unprecedented performance to address important key questions about the structure and dynamics of our universe across a large range of length scale… ▽ More The Arcus Probe mission concept has been submitted as an Astrophysics Probe Explorer candidate. It features two co-aligned high-resolution grating spectrometers: one for the soft x-ray band and one for the far UV. Together, these instruments can provide unprecedented performance to address important key questions about the structure and dynamics of our universe across a large range of length scales. The X-ray Spectrometer (XRS) consists of four parallel optical channels, each featuring an x-ray telescope with a fixed array of 216 lightweight, high-efficiency blazed transmission gratings, and two CCD readout arrays. Average spectral resolving power $λ/Δλ> 2,500$ ($\sim 3500$ expected) across the 12-50 Å\ band and combined effective area $> 350$ cm$^2$ ($> 470$ cm$^2$ expected) near OVII wavelengths are predicted, based on the measured x-ray performance of spectrometer prototypes and detailed ray trace modeling. We describe the optical and structural design of the grating arrays, from the macroscopic grating petals to the nanoscale gratings bars, grating fabrication, alignment, and x-ray testing. Recent x-ray diffraction efficiency results from chemically thinned grating bars are presented and show performance above mission assumptions. △ Less

Submitted 24 May, 2024; originally announced May 2024.

Comments: 30 pages, 11 figures, submitted to JATIS

Temporal characterization of laser pulses using an air-based knife-edge technique

Authors: Pierre Béjot, Rishabh Kumar Bhalavi, Adrien Leblanc, Antoine Dubrouil, Franck Billard, Olivier Faucher, Edouard Hertz

Abstract: We present the characterization of ultrashort laser pulses by using the plasma-induced frequency resolved optical switching (PI-FROSt) technique, implemented in ambient air. This recently developed method allows for a temporal reconstruction of a pulse at its focal spot by utilizing a moderately intense pump laser pulse for generating an ionization-induced ultrafast defocusing lens. When propagati… ▽ More We present the characterization of ultrashort laser pulses by using the plasma-induced frequency resolved optical switching (PI-FROSt) technique, implemented in ambient air. This recently developed method allows for a temporal reconstruction of a pulse at its focal spot by utilizing a moderately intense pump laser pulse for generating an ionization-induced ultrafast defocusing lens. When propagating through the produced plasma lens, the probe beam to characterize experiences an increase of its size in the far field. The spectrum of the defocused probe field, measured as a function of the pump-probe delay, allows for a comprehensive characterization of the temporal and spectral attributes of the pulse. We report herein the ability of this technique, initially designed for use in rare gases, to operate in ambient air conditions with similar performance. The method is remarkably straightforward to implement and requires no additional optical component other than a focusing mirror, while delivering laser pulse reconstructions of high reliability. △ Less

Submitted 22 April, 2024; originally announced April 2024.

The First Flight of the Marshall Grazing Incidence X-ray Spectrometer (MaGIXS)

Authors: Sabrina L. Savage, Amy R. Winebarger, Ken Kobayashi, P. S. Athiray, Dyana Beabout, Leon Golub, Robert W. Walsh, Brent Beabout, Stephen Bradshaw, Alexander R. Bruccoleri, Patrick R. Champey, Peter Cheimets, Jonathan Cirtain, Edward DeLuca, Giulio Del Zanna, Anthony Guillory, Harlan Haight, Ralf K. Heilmann, Edward Hertz, William Hogue, Jeffery Kegley, Jeffery Kolodziejczak, Chad Madsen, Helen Mason, David E. McKenzie , et al. (12 additional authors not shown)

Abstract: The Marshall Grazing Incidence X-ray Spectrometer (MaGIXS) sounding rocket experiment launched on July 30, 2021 from the White Sands Missile Range in New Mexico. MaGIXS is a unique solar observing telescope developed to capture X-ray spectral images, in the 6 - 24 Angstrom wavelength range, of coronal active regions. Its novel design takes advantage of recent technological advances related to fabr… ▽ More The Marshall Grazing Incidence X-ray Spectrometer (MaGIXS) sounding rocket experiment launched on July 30, 2021 from the White Sands Missile Range in New Mexico. MaGIXS is a unique solar observing telescope developed to capture X-ray spectral images, in the 6 - 24 Angstrom wavelength range, of coronal active regions. Its novel design takes advantage of recent technological advances related to fabricating and optimizing X-ray optical systems as well as breakthroughs in inversion methodologies necessary to create spectrally pure maps from overlapping spectral images. MaGIXS is the first instrument of its kind to provide spatially resolved soft X-ray spectra across a wide field of view. The plasma diagnostics available in this spectral regime make this instrument a powerful tool for probing solar coronal heating. This paper presents details from the first MaGIXS flight, the captured observations, the data processing and inversion techniques, and the first science results. △ Less

Submitted 7 December, 2022; v1 submitted 1 December, 2022; originally announced December 2022.

Comments: 20 pages, 18 figures

X-ray performance of critical-angle transmission grating prototypes for the Arcus mission

Authors: Ralf K. Heilmann, Alexander R. Bruccoleri, Vadim Burwitz, Casey deRoo, Alan Garner, Hans Moritz Guenther, Eric M. Gullikson, Gisela Hartner, Ed Hertz, Andreas Langmeier, Thomas Mueller, Surangkhana Rukdee, Thomas Schmidt, Randall K. Smith, Mark L. Schattenburg

Abstract: Arcus is a proposed soft x-ray grating spectrometer Explorer. It aims to explore cosmic feedback by mapping hot gases within and between galaxies and galaxy clusters and characterizing jets and winds from supermassive black holes, and to investigate the dynamics of protoplanetary discs and stellar accretion. Arcus features 12 m-focal-length grazing-incidence silicon pore optics (SPO) developed for… ▽ More Arcus is a proposed soft x-ray grating spectrometer Explorer. It aims to explore cosmic feedback by mapping hot gases within and between galaxies and galaxy clusters and characterizing jets and winds from supermassive black holes, and to investigate the dynamics of protoplanetary discs and stellar accretion. Arcus features 12 m-focal-length grazing-incidence silicon pore optics (SPO) developed for the Athena mission. Critical-angle transmission (CAT) gratings efficiently disperse high diffraction orders onto CCDs. We report new and improved x-ray performance results for Arcus-like CAT gratings, including record resolving power for two co-aligned CAT gratings. Multiple Arcus prototype grating facets were illuminated by an SPO at the PANTER facility. The facets consist of $32\times32.5$ mm$^2$ patterned silicon membranes, bonded to metal frames. The bonding angle is adjusted according to the measured average tilt angle of the grating bars in the membrane. Two simultaneously illuminated facets show minor broadening of the Al-K$_α$ doublet in 18$^{\rm th}$ and 21$^{\rm st}$ orders with a best fit record effective resolving power of $R_G \approx 1.3^{+\infty}_{-0.5}\times10^4$ ($3σ$), about 3-4 times the Arcus requirement. We measured the diffraction efficiency of quasi-fully illuminated gratings at O-K wavelengths in orders 4-7 in an Arcus-like configuration and compare results with synchrotron spot measurements. After corrections for geometrical effects and bremsstrahlung continuum we find agreement between full and spot illumination at the two different facilities, as well as with the models used for Arcus effective area predictions. We find that these flight-like gratings meet diffraction efficiency and greatly exceed resolving power Arcus requirements. △ Less

Submitted 17 June, 2022; originally announced June 2022.

Comments: 19 pages, 16 figures

TIGER: TIme-Gated Electric field Reconstruction

Authors: F. Billard, R. Sharma, E. Hertz, O. Faucher, P. Béjot

Abstract: We present a novel self-referenced method for the complete temporal characterization (phase and amplitude) of ultrashort optical laser pulses. The technique, called TIme-Gated Electric field Reconstruction (TIGER), measures a second-order nonlinear signal (namely, second harmonic generation or two-photon absorption) produced by four time-delayed replicas of the input pulse. The delays are spatiall… ▽ More We present a novel self-referenced method for the complete temporal characterization (phase and amplitude) of ultrashort optical laser pulses. The technique, called TIme-Gated Electric field Reconstruction (TIGER), measures a second-order nonlinear signal (namely, second harmonic generation or two-photon absorption) produced by four time-delayed replicas of the input pulse. The delays are spatially encoded in the beam profile using a four-faced pyramid-like optical element. The presented technique enables single shot measurement and does not require any spectral measurements, in contrast with well-known self-referenced characterization methods. Depending on the chosen geometry, the recorded TIGER signal can be either interferometric (i.e., carrier frequency resolved) or intensimetric. This paper describes the principle operation of the device together with a detailed theoretical analysis. TIGER measurements of various laser pulse shapes with their reconstructions are then presented demonstrating the relevance of this original approach. △ Less

Submitted 25 January, 2022; originally announced January 2022.

Comments: 10 pages, 14 figures

Visualizing coherent molecular rotation in a gaseous medium

Authors: Ilia Tutunnikov, Emilien Prost, Uri Steinitz, Pierre Béjot, Edouard Hertz, Franck Billard, Olivier Faucher, Ilya Sh. Averbukh

Abstract: Inducing and controlling the ultrafast molecular rotational dynamics using shaped laser fields is essential in numerous applications. Several approaches exist that allow following the coherent molecular motion in real-time, including Coulomb explosion-based techniques and recovering molecular orientation from the angular distribution of high harmonics. We theoretically consider a non-intrusive opt… ▽ More Inducing and controlling the ultrafast molecular rotational dynamics using shaped laser fields is essential in numerous applications. Several approaches exist that allow following the coherent molecular motion in real-time, including Coulomb explosion-based techniques and recovering molecular orientation from the angular distribution of high harmonics. We theoretically consider a non-intrusive optical scheme for visualizing the rotational dynamics in an anisotropic molecular gas. The proposed method allows determining the instantaneous orientation of the principal optical axes of the gas. The method is based on probing the sample using ultra-short circularly polarized laser pulses and recording the transmission image through a vortex wave plate. We consider two example excitations: molecular alignment induced by an intense linearly polarized laser pulse and unidirectional molecular rotation induced by a polarization-shaped pulse. The proposed optical method is promising for visualizing the dynamics of complex symmetric- and asymmetric-top molecules. △ Less

Submitted 26 September, 2021; v1 submitted 23 September, 2021; originally announced September 2021.

Comments: 12 pages, 14 figures

Journal ref: Phys. Rev. A 104, 053113 (2021)

Calibration of the MaGIXS experiment II: Flight Instrument Calibration

Authors: P. S. Athiray, Amy R. Winebarger, Patrick Champey, Ken Kobayashi, Sabrina Savage, Brent Beabout, Dyana Beabout, David Broadway, Alexander R. Bruccoleri, Peter Cheimets, Leon Golub, Eric Gullikson, Harlan Haight, Ralf K. Heilmann, Edward Hertz, William Hogue, Steven Johnson, Jeffrey Kegley, Jeffery Kolodziejczak, Chad Madsen, Mark L. Schattenburg, Richard Siler, Genevieve D. Vigil, Ernest Wright

Abstract: The Marshall Grazing Incidence X-ray Spectrometer (MaGIXS) is a sounding rocket experiment that observes the soft X-ray spectrum of the Sun from 6.0 - 24 Angstrom (0.5 - 2.0 keV), successfully launched on 30 July 2021. End-to-end alignment of the flight instrument and calibration experiments are carried out using the X-ray and Cryogenic Facility (XRCF) at NASA Marshall Space Flight Center. In this… ▽ More The Marshall Grazing Incidence X-ray Spectrometer (MaGIXS) is a sounding rocket experiment that observes the soft X-ray spectrum of the Sun from 6.0 - 24 Angstrom (0.5 - 2.0 keV), successfully launched on 30 July 2021. End-to-end alignment of the flight instrument and calibration experiments are carried out using the X-ray and Cryogenic Facility (XRCF) at NASA Marshall Space Flight Center. In this paper, we present the calibration experiments of MaGIXS, which include wavelength calibration, measurement of line spread function, and determination of effective area. Finally, we use the measured instrument response function to predict the expected count rates for MaGIXS flight observation looking at a typical solar active region △ Less

Submitted 3 September, 2021; originally announced September 2021.

Comments: 20 pages, 16 figures, Accepted for publication in the Astrophysical Journal

Doppler effect as a tool for ultrashort electric field reconstruction

Authors: P. Béjot, E. Szmygel, A. Dubrouil, F. Billard, B. Lavorel, O. Faucher, E. Hertz

Abstract: Technological advances in femtosecond laser sources call for the development of increasingly refined characterization tools implying to enrich the existing panel of operable nonlinear interactions. The present paper describes a novel characterization method based on spectral-shearing interferometry which exploits the non-standard rotational Doppler effect for producing the frequency shear. This or… ▽ More Technological advances in femtosecond laser sources call for the development of increasingly refined characterization tools implying to enrich the existing panel of operable nonlinear interactions. The present paper describes a novel characterization method based on spectral-shearing interferometry which exploits the non-standard rotational Doppler effect for producing the frequency shear. This original approach, called DEER "Doppler Effect for Electric field Reconstruction", provides a spectral-shearing in the absence of frequency conversion and features multiple benefits as for instance the ability of operation in the ultraviolet spectral range or the characterization of ultra-broadband laser pulses. △ Less

Submitted 3 March, 2020; originally announced March 2020.

Comments: 7 pages, 3 figures

Molecular alignment echoes probe collision-induced rotational-speed changes

Authors: J. -M. Hartmann, J. Ma, T. Delahaye, F. Billard, E. Hertz, J. Wu, B. Lavorel, C. Boulet, O. Faucher

Abstract: We show that the decays with pressure of the alignment echoes induced in N2O-He gas mixtures by two laser pulses with various delays bring detailed information on collision-induced changes of the rotational speed. Measurements and calculations demonstrate that collisions reduce the echo amplitude all the more efficiently when the echo appears late. We quantitatively explain this behavior by the fi… ▽ More We show that the decays with pressure of the alignment echoes induced in N2O-He gas mixtures by two laser pulses with various delays bring detailed information on collision-induced changes of the rotational speed. Measurements and calculations demonstrate that collisions reduce the echo amplitude all the more efficiently when the echo appears late. We quantitatively explain this behavior by the filamentation of the classical rotational phase space induced by the first pulse and the progressive narrowing of the filaments with time. The variation of the echo decay thus reflects the ability of collisions to change the molecules' rotational speed by various amounts, enabling refined tests of models for the dissipation induced by intermolecular forces. △ Less

Submitted 29 May, 2020; v1 submitted 4 February, 2020; originally announced February 2020.

Journal ref: Phys. Rev. Research 2, 023247 (2020)

Optical imaging of coherent molecular rotors

Authors: Jérémy Bert, Emilien Prost, Ilia Tutunnikov, Pierre Béjot, Edouard Hertz, Franck Billard, Bruno Lavorel, Uri Steinitz, Ilya Sh. Averbukh, Olivier Faucher

Abstract: Short laser pulses are widely used for controlling molecular rotational degrees of freedom and inducing molecular alignment, orientation, unidirectional rotation and other types of coherent rotational motion. To follow the ultra-fast rotational dynamics in real time, several techniques for producing molecular movies have been proposed based on the Coulomb explosion of rotating molecules, or recove… ▽ More Short laser pulses are widely used for controlling molecular rotational degrees of freedom and inducing molecular alignment, orientation, unidirectional rotation and other types of coherent rotational motion. To follow the ultra-fast rotational dynamics in real time, several techniques for producing molecular movies have been proposed based on the Coulomb explosion of rotating molecules, or recovering molecular orientation from the angular distribution of high-harmonics. The present work offers and demonstrates a novel non-destructive optical method for direct visualization and recording of movies of coherent rotational dynamics in a molecular gas. The technique is based on imaging the time-dependent polarization dynamics of a probe light propagating through a gas of coherently rotating molecules. The probe pulse continues through a radial polarizer, and is then recorded by a camera. We illustrate the technique by implementing it with two examples of time-resolved rotational dynamics: alignment-antialignment cycles in a molecular gas excited by a single linearly polarized laser pulse, and unidirectional molecular rotation induced by a pulse with twisted polarization. This method may open new avenues in studies on fast chemical transformation phenomena and ultrafast molecular dynamics caused by strong laser fields of various complexities. △ Less

Submitted 6 December, 2019; originally announced December 2019.

Journal ref: Laser & Photonics Reviews 14, 1900344 (2020)

Observing collisions beyond the secular approximation limit

Authors: J. Ma, H. Zhang, B. Lavorel, F. Billard, E. Hertz, J. Wu, C. Boulet, J. -M. Hartmann, O. Faucher

Abstract: Energy transfer through quantum coherences plays an essential role in diverse natural phenomena and technological applications, such as human vision, light-harvesting complexes, quantum heat engines, and quantum information and computing. The understanding of the long-lived coherence involved in these phenomena requires a detailed modeling of the system-bath interactions beyond the so-called secul… ▽ More Energy transfer through quantum coherences plays an essential role in diverse natural phenomena and technological applications, such as human vision, light-harvesting complexes, quantum heat engines, and quantum information and computing. The understanding of the long-lived coherence involved in these phenomena requires a detailed modeling of the system-bath interactions beyond the so-called secular and/or Markovian approximations. Despite continuous theoretical progress on understanding nonsecular dynamics in the last decades, convincing experimental observations are still lacking. By using the laser-kicked molecular rotor as a model system, we here experimentally unveil the nonsecular dynamics in the rotational relaxation of molecules due to thermal collisions. Specifically, the rotational coherence in gas-phase molecules is systematically probed and characterized by the recently discovered rotational alignment echoes featuring a decoherence and dissipation process which can only be explained by the nonsecular quantum master equations for modeling molecular collisions. △ Less

Submitted 7 December, 2019; v1 submitted 26 August, 2019; originally announced August 2019.

Polarization shaping of high-order harmonics in laser-aligned molecules

Authors: E. Skantzakis, S. Chatziathansiou, P. A. Carpeggiani, G. Sansone, A. Nayak, D. Gray, P. Tzallas, D. Charalambidis, E. Hertz, O. Faucher

Abstract: The present work reports on the generation of short-pulse coherent extreme ultraviolet radiation of controlled polarization. The proposed strategy is based on high-order harmonics generated in pre-aligned molecules. Field-free molecular alignment produced by a short linearly-polarized infrared laser pulse is used to break the isotropy of a gas medium. Driving the aligned molecules by a circularly-… ▽ More The present work reports on the generation of short-pulse coherent extreme ultraviolet radiation of controlled polarization. The proposed strategy is based on high-order harmonics generated in pre-aligned molecules. Field-free molecular alignment produced by a short linearly-polarized infrared laser pulse is used to break the isotropy of a gas medium. Driving the aligned molecules by a circularly-polarized infrared pulse allows to transfer the anisotropy of the medium to the polarization of the generated harmonic light. The ellipticity of the latter is controlled by adjusting the angular distribution of the molecules at the time they interact with the driving pulse. Extreme ultraviolet radiation produced with high degree of ellipticity (close to circular) is demonstrated. △ Less

Submitted 28 February, 2019; originally announced March 2019.

Journal ref: Scientific Reports volume 6, Article number: 39295 (2016)

On the observation of field-free orientation of a symmetric top molecule by terahertz laser pulses at high temperature

Authors: P. Babilotte, K. Hamraoui, F. Billard, E. Hertz, B. Lavorel, O. Faucher, D. Sugny

Abstract: We investigate experimentally and numerically the field-free orientation of the symmetric top molecule of methyl-iodide at high temperature using a terahertz radiation generated by a plasma induced by a two-color laser beam. The degree of orientation is measured from the free-induction decay emitted by the sample. The observed experimental signal is reproduced with a good accuracy by numerical sim… ▽ More We investigate experimentally and numerically the field-free orientation of the symmetric top molecule of methyl-iodide at high temperature using a terahertz radiation generated by a plasma induced by a two-color laser beam. The degree of orientation is measured from the free-induction decay emitted by the sample. The observed experimental signal is reproduced with a good accuracy by numerical simulations. △ Less

Submitted 4 October, 2016; originally announced October 2016.

Comments: 16 pages, 7 figures

Journal ref: Phys. Rev. A 94, 043403 (2016)

Fractional Echoes

Authors: G. Karras, E. Hertz, F. Billard, B. Lavorel, G. Siour, J. -M. Hartmann, O. Faucher, Erez Gershnabel, Yehiam Prior, Ilya Sh. Averbukh

Abstract: We report the observation of fractional echoes in a double-pulse excited nonlinear system. Unlike standard echoes which appear periodically at delays which are integer multiple of the delay between the two exciting pulses, the fractional echoes appear at rational fractions of this delay. We discuss the mechanism leading to this phenomenon, and provide the first experimental demonstration of fracti… ▽ More We report the observation of fractional echoes in a double-pulse excited nonlinear system. Unlike standard echoes which appear periodically at delays which are integer multiple of the delay between the two exciting pulses, the fractional echoes appear at rational fractions of this delay. We discuss the mechanism leading to this phenomenon, and provide the first experimental demonstration of fractional echoes by measuring third harmonic generation in a thermal gas of CO2 molecules excited by a pair of femtosecond laser pulses. △ Less

Submitted 3 March, 2016; originally announced March 2016.

Journal ref: Phys. Rev. A 94, 033404 (2016)

Dynamics, effciency and energy distribution of nonlinear plasmon-assisted generation of hot carriers

Authors: O. Demichel, M. Petit, S. Viarbitskaya, R. Mejard, F. de Fornel, E. Hertz, F. Billard, A. Bouhelier, B. Cluzel

Abstract: We employ nonlinear autocorrelation measurements to investigate plasmon-assisted hot carrier dynamics generated in optical gold antennas. We demonstrate that surface plasmons enable a nonlinear formation of hot carriers, providing thus a unique lever to optimize the energy distribution and generation efficiency of the photo-excited charges. The temporal response of the carriers' relaxation can be… ▽ More We employ nonlinear autocorrelation measurements to investigate plasmon-assisted hot carrier dynamics generated in optical gold antennas. We demonstrate that surface plasmons enable a nonlinear formation of hot carriers, providing thus a unique lever to optimize the energy distribution and generation efficiency of the photo-excited charges. The temporal response of the carriers' relaxation can be controlled within a range extending from 500~fs to 2.5~ps. By conducting a quantitative analysis of the dynamics, we determine the nonlinear absorption cross-section of individual optical antennas. As such, this work provides strong insights on the understanding of plasmon-induced hot carrier generation, especially in the view of applications where the time response plays a preponderant role. △ Less

Submitted 12 January, 2016; originally announced January 2016.

Selective excitation of bright and dark plasmonic resonances of single gold nanorods

Authors: O. Demichel, M. Petit, G. Colas des Francs, A. Bouhelier, E. Hertz, F. Billard, F. de Fornel, B. Cluzel

Abstract: Plasmonic dark modes are pure near-field resonances since their dipole moments are vanishing in far field. These modes are particularly interesting to enhance nonlinear light-matter interaction at the nanometer scale because radiative losses are mitigated therefore increasing the intrinsic lifetime of the resonances. However, the excitation of dark modes by standard far field approaches is general… ▽ More Plasmonic dark modes are pure near-field resonances since their dipole moments are vanishing in far field. These modes are particularly interesting to enhance nonlinear light-matter interaction at the nanometer scale because radiative losses are mitigated therefore increasing the intrinsic lifetime of the resonances. However, the excitation of dark modes by standard far field approaches is generally inefficient because the symmetry of the electromagnetic near-field distribution has a poor overlap with the excitation field. Here, we demonstrate the selective optical excitation of bright and dark plasmonic modes of single gold nanorods by spatial phase-shaping the excitation beam. Using two-photon luminescence measurements, we unambiguously identify the symmetry and the order of the emitting modes and analyze their angular distribution by Fourier-space imaging. △ Less

Submitted 23 September, 2015; originally announced September 2015.

Journal ref: Optics Express Vol. 22, Issue 12, pp. 15088-15096 (2014)

Orientation and Alignment Echoes

Authors: G. Karras, E. Hertz, F. Billard, B. Lavorel, J. -M. Hartmann, O. Faucher, E. Gershnabel, Y. Prior, I. Sh. Averbukh

Abstract: We present what is probably the simplest classical system featuring the echo phenomenon - a collection of randomly oriented free rotors with dispersed rotational velocities. Following excitation by a pair of time-delayed impulsive kicks, the mean orientation/alignment of the ensemble exhibits multiple echoes and fractional echoes. We elucidate the mechanism of the echo formation by kick-induced fi… ▽ More We present what is probably the simplest classical system featuring the echo phenomenon - a collection of randomly oriented free rotors with dispersed rotational velocities. Following excitation by a pair of time-delayed impulsive kicks, the mean orientation/alignment of the ensemble exhibits multiple echoes and fractional echoes. We elucidate the mechanism of the echo formation by kick-induced filamentation of phase space, and provide the first experimental demonstration of classical alignment echoes in a thermal gas of CO_2 molecules excited by a pair of femtosecond laser pulses. △ Less

Submitted 27 January, 2015; originally announced February 2015.

Subcycle engineering of laser filamentation in gas by harmonic seeding

Authors: P. Béjot, G. Karras, F. Billard, J. Doussot, E. Hertz, B. Lavorel, O. Faucher

Abstract: Manipulating at will the propagation dynamics of high power laser pulses is a long-standing dream whose accomplishment would lead to the control of a plethora of fascinating physical phenomena emerging from laser-matter interaction. The present work represents a significant step towards such an ideal control by manipulating the nonlinear optical properties of the gas medium at the quantum level. T… ▽ More Manipulating at will the propagation dynamics of high power laser pulses is a long-standing dream whose accomplishment would lead to the control of a plethora of fascinating physical phenomena emerging from laser-matter interaction. The present work represents a significant step towards such an ideal control by manipulating the nonlinear optical properties of the gas medium at the quantum level. This is accomplished by engineering the intense laser pulse experiencing filamentation at the subcycle level with a relatively weak (about 1%) third-harmonic radiation. The control results from quantum interferences between a single and a two-color (mixing the fundamental frequency with its 3rd harmonic) ionization channel. This mechanism, which depends on the relative phase between the two electric fields, is responsible for wide refractive index modifications in relation with significant enhancement or suppression of the ionization rate. As a first application, we demonstrate the production and control of an axially modulated plasma channel that could be used for quasi-phase matched laser wakefield acceleration. △ Less

Submitted 17 November, 2014; originally announced November 2014.

Comments: 7 pages, 4 figures

Journal ref: Phys. Rev. A 92, 053417 (2015)

Harmonic generation and filamentation: when secondary radiations have primary consequences

Authors: P. Béjot, G. Karras, F. Billard, E. Hertz, B. Lavorel, E. Cormier, O. Faucher

Abstract: In this Letter, it is experimentally and theoretically shown that weak odd harmonics generated during the propagation of an infrared ultrashort ultra-intense pulse unexpectedly modify the nonlinear properties of the medium and lead to a strong modification of the propagation dynamics. This result is in contrast with all current state-of-the-art propagation model predictions, in which secondary rad… ▽ More In this Letter, it is experimentally and theoretically shown that weak odd harmonics generated during the propagation of an infrared ultrashort ultra-intense pulse unexpectedly modify the nonlinear properties of the medium and lead to a strong modification of the propagation dynamics. This result is in contrast with all current state-of-the-art propagation model predictions, in which secondary radiations, such as third harmonic, are expected to have a negligible action upon the fundamental pulse propagation. By analysing full three-dimensional ab initio quantum calculations describing the microscopic atomic optical response, we have identified a fundamental mechanism resulting from interferences between a direct ionization channel and a channel involving one single ultraviolet photon. This mechanism is responsible for wide refractive index modifications in relation with significant variation of the ionization rate. This work paves the way to the full physical understanding of the filamentation mechanism and could lead to unexplored phenomena, such as coherent control of the filamentation by harmonic seeding. △ Less

Submitted 14 February, 2014; originally announced February 2014.

Comments: 7 pages, 5 figures

The Interface Region Imaging Spectrograph (IRIS)

Authors: B. De Pontieu, A. M. Title, J. Lemen, G. D. Kushner, D. J. Akin, B. Allard, T. Berger, P. Boerner, M. Cheung, C. Chou, J. F. Drake, D. W. Duncan, S. Freeland, G. F. Heyman, C. Hoffman, N. E. Hurlburt, R. W. Lindgren, D. Mathur, R. Rehse, D. Sabolish, R. Seguin, C. J. Schrijver, T. D. Tarbell, J. -P. Wuelser, C. J. Wolfson , et al. (63 additional authors not shown)

Abstract: The Interface Region Imaging Spectrograph (IRIS) small explorer spacecraft provides simultaneous spectra and images of the photosphere, chromosphere, transition region, and corona with 0.33-0.4 arcsec spatial resolution, 2 s temporal resolution and 1 km/s velocity resolution over a field-of-view of up to 175 arcsec x 175 arcsec. IRIS was launched into a Sun-synchronous orbit on 27 June 2013 using… ▽ More The Interface Region Imaging Spectrograph (IRIS) small explorer spacecraft provides simultaneous spectra and images of the photosphere, chromosphere, transition region, and corona with 0.33-0.4 arcsec spatial resolution, 2 s temporal resolution and 1 km/s velocity resolution over a field-of-view of up to 175 arcsec x 175 arcsec. IRIS was launched into a Sun-synchronous orbit on 27 June 2013 using a Pegasus-XL rocket and consists of a 19-cm UV telescope that feeds a slit-based dual-bandpass imaging spectrograph. IRIS obtains spectra in passbands from 1332-1358, 1389-1407 and 2783-2834 Angstrom including bright spectral lines formed in the chromosphere (Mg II h 2803 Angstrom and Mg II k 2796 Angstrom) and transition region (C II 1334/1335 Angstrom and Si IV 1394/1403 Angstrom). Slit-jaw images in four different passbands (C II 1330, Si IV 1400, Mg II k 2796 and Mg II wing 2830 Angstrom) can be taken simultaneously with spectral rasters that sample regions up to 130 arcsec x 175 arcsec at a variety of spatial samplings (from 0.33 arcsec and up). IRIS is sensitive to emission from plasma at temperatures between 5000 K and 10 MK and will advance our understanding of the flow of mass and energy through an interface region, formed by the chromosphere and transition region, between the photosphere and corona. This highly structured and dynamic region not only acts as the conduit of all mass and energy feeding into the corona and solar wind, it also requires an order of magnitude more energy to heat than the corona and solar wind combined. The IRIS investigation includes a strong numerical modeling component based on advanced radiative-MHD codes to facilitate interpretation of observations of this complex region. Approximately eight Gbytes of data (after compression) are acquired by IRIS each day and made available for unrestricted use within a few days of the observation. △ Less

Submitted 10 January, 2014; originally announced January 2014.

Comments: 53 pages, 15 figures

On the interpretation of negative birefringence observed in strong-field optical pump-probe experiments: high-order Kerr and plasma grating effects

Authors: G. Karras, P. Béjot, J. Houzet, E. Hertz, F. Billard, B. Lavorel, O. Faucher

Abstract: The analysis of negative birefringence optically induced in major air components (Loriot et al., [1, 2]) is revisited in light of the recently reported plasma grating-induced phase-shift effect predicted for strong field pump-probe experiments (Wahlstrand and Milchberg, [3]). The nonlinear birefrin- gence induced by a short and intense laser pulse in argon is measured by femtosecond time-resolved… ▽ More The analysis of negative birefringence optically induced in major air components (Loriot et al., [1, 2]) is revisited in light of the recently reported plasma grating-induced phase-shift effect predicted for strong field pump-probe experiments (Wahlstrand and Milchberg, [3]). The nonlinear birefrin- gence induced by a short and intense laser pulse in argon is measured by femtosecond time-resolved polarimetry. The experiments are performed with degenerate colors, where the pump and probe beam share the same spectrum, or with two different colors and non-overlapping spectra. The in- terpretation of the experimental results is substantiated using a numerical 3D+1 model accounting for nonlinear propagation effects, cross-beam geometry of the interacting laser pulses, and detec- tion technique. The model also includes the ionization rate of argon and high-order Kerr indices introduced by Loriot et al. enabling to assess the contribution of both terms to the observed effect. The results show that the ionization-induced phase-shift has a minor contribution compared to the high-order Kerr effect formerly introduced, the latter allowing a reasonably good reproduction of the experimental data for the present conditions. △ Less

Submitted 7 November, 2013; originally announced November 2013.

Comments: 10 pages, 11 figures

Revisiting interferences for measuring and optimizing optical nonlinearities

Authors: F. Billard, P. Béjot, E. Hertz, B. Lavorel, O. Faucher

Abstract: A method based on optical interferences for measuring optical nonlinearities is presented. In a proof-of-principle experiment, the technique is applied to the experimental determination of the intensity dependence of the photoionization process. It is shown that it can also be used to control and optimize the nonlinear process itself at constant input energy. The presented strategy leads to enhanc… ▽ More A method based on optical interferences for measuring optical nonlinearities is presented. In a proof-of-principle experiment, the technique is applied to the experimental determination of the intensity dependence of the photoionization process. It is shown that it can also be used to control and optimize the nonlinear process itself at constant input energy. The presented strategy leads to enhancements that can reach several orders of magnitude for highly nonlinear processes. △ Less

Submitted 18 February, 2013; originally announced February 2013.

Comments: 6 pages, 5 figures

Journal ref: Phys. Rev. A 88, 013854 (2013)

MMT & Magellan Infrared Spectrograph

Authors: Brian McLeod, Daniel Fabricant, George Nystrom, Ken McCracken, Stephen Amato, Henry Bergner, Warren Brown, Michael Burke, Igor Chilingarian, Maureen Conroy, Dylan Curley, Gabor Furesz, John Geary, Edward Hertz, Justin Holwell, Anne Matthews, Tim Norton, Sang Park, John Roll, Joseph Zajac, Harland Epps, Paul Martini

Abstract: The MMT and Magellan infrared spectrograph (MMIRS) is a cryogenic multiple slit spectrograph operating in the wavelength range 0.9-2.4 micron. MMIRS' refractive optics offer a 6.9 by 6.9 arcmin field of view for imaging with a spatial resolution of 0.2 arcsec per pixel on a HAWAII-2 array. For spectroscopy, MMIRS can be used with long slits up to 6.9 arcmin long, or with custom slit masks having s… ▽ More The MMT and Magellan infrared spectrograph (MMIRS) is a cryogenic multiple slit spectrograph operating in the wavelength range 0.9-2.4 micron. MMIRS' refractive optics offer a 6.9 by 6.9 arcmin field of view for imaging with a spatial resolution of 0.2 arcsec per pixel on a HAWAII-2 array. For spectroscopy, MMIRS can be used with long slits up to 6.9 arcmin long, or with custom slit masks having slitlets distributed over a 4 by 6.9 arcmin area. A range of dispersers offer spectral resolutions of 800 to 3000. MMIRS is designed to be used at the f/5 foci of the MMT or Magellan Clay 6.5m telescopes. MMIRS was commissioned in 2009 at the MMT and has been in routine operation at the Magellan Clay Telescope since 2010. MMIRS is being used for a wide range of scientific investigations from exoplanet atmospheres to Ly-alpha emitters. △ Less

Submitted 26 November, 2012; originally announced November 2012.

Comments: 43 pages, including 11 figures, accepted for publication in PASP

Journal ref: PASP (2012), 124, 1318

High-field quantum calculation reveals time-dependent negative Kerr contribution

Authors: Pierre Béjot, Eric Cormier, Edouard Hertz, Bruno Lavorel, Jérôme Kasparian, Jean-Pierre Wolf, Olivier Faucher

Abstract: The exact quantum time-dependent optical response of hydrogen under strong field near infrared excitation is investigated and compared to the perturbative model widely used for describing the effective atomic polarization induced by intense laser fields. By solving the full 3D time-dependent Schrödinger equation, we exhibit a supplementary, quasi-instantaneous defocusing contribution missing in th… ▽ More The exact quantum time-dependent optical response of hydrogen under strong field near infrared excitation is investigated and compared to the perturbative model widely used for describing the effective atomic polarization induced by intense laser fields. By solving the full 3D time-dependent Schrödinger equation, we exhibit a supplementary, quasi-instantaneous defocusing contribution missing in the weak-field model of polarization. We show that this effect is far from being negligible in particular when closures of ionization channels occur and stems from the interaction of electrons with their parent ions. It provides an interpretation to higher-order Kerr effect recently observed in various gases. △ Less

Submitted 7 January, 2013; v1 submitted 21 June, 2012; originally announced June 2012.

Comments: 5 pages, 4 figures

Journal ref: Phys. Rev. Lett. 110, 043902 (2013)

Transition from plasma- to Kerr-driven laser filamentation

Authors: Pierre Béjot, Edouard Hertz, Jérôme Kasparian, Bruno Lavorel, Jean-Pierre Wolf, Olivier Faucher

Abstract: While filaments are generally interpreted as a dynamic balance between Kerr focusing and plasma defocusing, the role of the higher-order Kerr effect (HOKE) is actively debated as a potentially dominant defocusing contribution to filament stabilization. In a pump-probe experiment supported by numerical simulations, we demonstrate the transition between two distinct filamentation regimes at 800\,nm.… ▽ More While filaments are generally interpreted as a dynamic balance between Kerr focusing and plasma defocusing, the role of the higher-order Kerr effect (HOKE) is actively debated as a potentially dominant defocusing contribution to filament stabilization. In a pump-probe experiment supported by numerical simulations, we demonstrate the transition between two distinct filamentation regimes at 800\,nm. For long pulses (1.2 ps), the plasma substantially contributes to filamentation, while this contribution vanishes for short pulses (70 fs). These results confirm the occurrence, in adequate conditions, of filamentation driven by the HOKE rather than by plasma. △ Less

Submitted 13 May, 2011; v1 submitted 8 March, 2011; originally announced March 2011.

Comments: 6 pages, 4 figures. Accepted for publication in Physical Review Letters

Journal ref: Physical Review Letters 106, 243902 (2011)

From higher-order Kerr nonlinearities to quantitative modeling of 3rd and 5th harmonic generation in argon

Authors: P. Béjot, E. Hertz, B. Lavorel, J. Kasparian, J. -P. Wolf, O. Faucher

Abstract: The recent measurement of negative higher-order Kerr effect (HOKE) terms in gases has given rise to a controversial debate, fed by its impact on short laser pulse propagation. By comparing the experimentally measured yield of the third and fifth harmonics, with both an analytical and a full comprehensive numerical propagation model, we confirm the absolute and relative values of the reported HOKE… ▽ More The recent measurement of negative higher-order Kerr effect (HOKE) terms in gases has given rise to a controversial debate, fed by its impact on short laser pulse propagation. By comparing the experimentally measured yield of the third and fifth harmonics, with both an analytical and a full comprehensive numerical propagation model, we confirm the absolute and relative values of the reported HOKE indices. △ Less

Submitted 11 March, 2011; v1 submitted 8 December, 2010; originally announced December 2010.

Comments: 3 pages, 2 figures

Higher-order Kerr terms allow ionization-free filamentation in gases

Authors: P. Béjot, J. Kasparian, S. Henin, V. Loriot, T. Vieillard, E. Hertz, O. Faucher, B. Lavorel, J. -P. Wolf

Abstract: We show that higher-order nonlinear indices ($n_4$, $n_6$, $n_8$, $n_{10}$) provide the main defocusing contribution to self-channeling of ultrashort laser pulses in air and Argon at 800 nm, in contrast with the previously accepted mechanism of filamentation where plasma was considered as the dominant defocusing process. Their consideration allows to reproduce experimentally observed intensities a… ▽ More We show that higher-order nonlinear indices ($n_4$, $n_6$, $n_8$, $n_{10}$) provide the main defocusing contribution to self-channeling of ultrashort laser pulses in air and Argon at 800 nm, in contrast with the previously accepted mechanism of filamentation where plasma was considered as the dominant defocusing process. Their consideration allows to reproduce experimentally observed intensities and plasma densities in self-guided filaments. △ Less

Submitted 6 November, 2010; originally announced November 2010.

Comments: 11 pages, 6 figures (11 panels)

Journal ref: Physical Review Letters 104, 103903 (2010)

Spectral dependence of purely-Kerr driven filamentation in air and argon

Authors: W. Ettoumi, P. Béjot, Y. Petit, V. Loriot, E. Hertz, O. Faucher, B. Lavorel, J. Kasparian, J. -P. Wolf

Abstract: Based on numerical simulations, we show that higher-order nonlinear indices (up to $n_8$ and $n_{10}$, respectively) of air and argon have a dominant contribution to both focusing and defocusing in the self-guiding of ultrashort laser pulses over most of the spectrum. Plasma generation and filamentation are therefore decoupled. As a consequence, ultraviolet wavelength may not be the optimal wavele… ▽ More Based on numerical simulations, we show that higher-order nonlinear indices (up to $n_8$ and $n_{10}$, respectively) of air and argon have a dominant contribution to both focusing and defocusing in the self-guiding of ultrashort laser pulses over most of the spectrum. Plasma generation and filamentation are therefore decoupled. As a consequence, ultraviolet wavelength may not be the optimal wavelengths for applications requiring to maximize ionization. △ Less

Submitted 6 November, 2010; originally announced November 2010.

Comments: 14 pages, 4 figures (14 panels)

Journal ref: Physical Review A 82, 033826 (2010)

On negative higher-order Kerr effect and filamentation

Authors: V. Loriot, P. Béjot, W. Ettoumi, Y. Petit, J. Kasparian, S. ~Henin, E. Hertz, B. Lavorel, O. Faucher, J. -P. ~Wolf

Abstract: As a contribution to the ongoing controversy about the role of higher-order Kerr effect (HOKE) in laser filamentation, we first provide thorough details about the protocol that has been employed to infer the HOKE indices from the experiment. Next, we discuss potential sources of artifact in the experimental measurements of these terms and show that neither the value of the observed birefringence,… ▽ More As a contribution to the ongoing controversy about the role of higher-order Kerr effect (HOKE) in laser filamentation, we first provide thorough details about the protocol that has been employed to infer the HOKE indices from the experiment. Next, we discuss potential sources of artifact in the experimental measurements of these terms and show that neither the value of the observed birefringence, nor its inversion, nor the intensity at which it is observed, appear to be flawed. Furthermore, we argue that, independently on our values, the principle of including HOKE is straightforward. Due to the different temporal and spectral dynamics, the respective efficiency of defocusing by the plasma and by the HOKE is expected to depend substantially on both incident wavelength and pulse duration. The discussion should therefore focus on defining the conditions where each filamentation regime dominates. △ Less

Submitted 3 November, 2010; originally announced November 2010.

Comments: 22 pages, 11 figures. Submitted to Laser physics as proceedings of the Laser Physics 2010 conference

Field-free molecular alignment induced by elliptically polarized laser pulses: non invasive 3 dimensional characterization

Authors: E. Hertz, D. Daems, S. Guérin, H. R. Jauslin, B. Lavorel, O. Faucher

Abstract: An investigation of field-free molecular alignment produced by elliptically polarized laser pulses is reported. Experiments are conducted in CO$_2$ at room temperature. A non invasive all-optical technique, based on the cross defocusing of a probe pulse, is used to measure the alignment along two orthogonal directions that is sufficient to provide a 3 dimensional characterization. The field-free… ▽ More An investigation of field-free molecular alignment produced by elliptically polarized laser pulses is reported. Experiments are conducted in CO$_2$ at room temperature. A non invasive all-optical technique, based on the cross defocusing of a probe pulse, is used to measure the alignment along two orthogonal directions that is sufficient to provide a 3 dimensional characterization. The field-free molecular alignment produced by a laser of elliptical polarization is in good agreement in terms of amplitude and shape with theoretical predictions. It turns out to be almost equivalent to the superposition of the effects that one would obtain with two individual cross-polarized pulses. The investigation highlights notably the occurrence of field-free two-direction alignment alternation for a suitably chosen degree of ellipticity. The analogy between this specific ellipticity and the well known "magic angle" used in time resolved spectroscopy to prevent rotational contributions is discussed. △ Less

Submitted 17 December, 2008; originally announced December 2008.

Comments: 6 pages, 4 figures

Journal ref: Phys. Rev. A 76, 043423 (2007)

Ultimate field-free molecular alignment by combined adiabatic-impulsive field design

Authors: S. Guerin, A. Rouzee, E. Hertz

Abstract: We show that a laser pulse designed as an adiabatic ramp followed by a kick allows one to reach a perfect postpulse molecular alignment, free of saturation. The mechanism is based on an optimized distribution of the energy between a weakly efficient but non saturating adiabatic ramp and an efficient but saturating impulsive field. Unprecedent degrees of alignment are predicted using state-of-the… ▽ More We show that a laser pulse designed as an adiabatic ramp followed by a kick allows one to reach a perfect postpulse molecular alignment, free of saturation. The mechanism is based on an optimized distribution of the energy between a weakly efficient but non saturating adiabatic ramp and an efficient but saturating impulsive field. Unprecedent degrees of alignment are predicted using state-of-the-art pulse shaping techniques and non-destructive field intensities. The scheme can be extended to reach high degrees of orientation of polar molecules using designed half-cycle pulses. △ Less

Submitted 5 March, 2008; originally announced March 2008.

Comments: 5 pages, 4 pages

Field-free two-direction alignment alternation of linear molecules by elliptic laser pulses

Authors: D. Daems, S. Guérin, E. Hertz, H. R. Jauslin, B. Lavorel, O. Faucher

Abstract: We show that a linear molecule subjected to a short specific elliptically polarized laser field yields postpulse revivals exhibiting alignment alternatively located along the orthogonal axis and the major axis of the ellipse. The effect is experimentally demonstrated by measuring the optical Kerr effect along two different axes. The conditions ensuring an optimal field-free alternation of high a… ▽ More We show that a linear molecule subjected to a short specific elliptically polarized laser field yields postpulse revivals exhibiting alignment alternatively located along the orthogonal axis and the major axis of the ellipse. The effect is experimentally demonstrated by measuring the optical Kerr effect along two different axes. The conditions ensuring an optimal field-free alternation of high alignments along both directions are derived. △ Less

Submitted 23 August, 2005; originally announced August 2005.

Comments: 5 pages, 4 color figures

Journal ref: Phys. Rev. Lett. 95, 063005 (2005)

Hectospec, the MMT's 300 Optical Fiber-Fed Spectrograph

Authors: Daniel Fabricant, Robert Fata, John Roll, Edward Hertz, Nelson Caldwell, Thomas Gauron, John Geary, Brian McLeod, Andrew Szentgyorgyi

Abstract: The Hectospec is a 300 optical fiber fed spectrograph commissioned at the MMT in the spring of 2004. A pair of high-speed six-axis robots move the 300 fiber buttons between observing configurations within ~300 s and to an accuracy ~25 microns. The optical fibers run for 26 m between the MMT's focal surface and the bench spectrograph operating at R~1000-2000. Another high dispersion bench spectro… ▽ More The Hectospec is a 300 optical fiber fed spectrograph commissioned at the MMT in the spring of 2004. A pair of high-speed six-axis robots move the 300 fiber buttons between observing configurations within ~300 s and to an accuracy ~25 microns. The optical fibers run for 26 m between the MMT's focal surface and the bench spectrograph operating at R~1000-2000. Another high dispersion bench spectrograph offering R~5,000, Hectochelle, is also available. The system throughput, including all losses in the telescope optics, fibers, and spectrograph peaks at ~10% at the grating blaze in 1" FWHM seeing. Correcting for aperture losses at the 1.5" diameter fiber entrance aperture, the system throughput peaks at $\sim$17%. Hectospec has proven to be a workhorse instrument at the MMT. Hectospec and Hectochelle together were scheduled for 1/3 of the available nights since its commissioning. Hectospec has returned \~60,000 reduced spectra for 16 scientific programs during its first year of operation. △ Less

Submitted 25 August, 2005; originally announced August 2005.

Comments: 68 pages, 28 figures, to appear in December 2005 PASP

Journal ref: Publ.Astron.Soc.Pac.117:1411-1434,2005