Publications

2018
Rivas, D.E., et al. Propagation-enhanced generation of intense high-harmonic continua in the 100-eV spectral region. Optica 5, 10, 1283–1289 (2018). Publisher's VersionAbstract
The study of core electron dynamics through nonlinear spectroscopy requires intense isolated attosecond extreme ultraviolet or even X-ray pulses. A robust way to produce these pulses is high-harmonic generation (HHG) in a gas medium. However, the energy upscaling of the process depends on a very demanding next-generation laser technology that provides multi-terawatt (TW) laser pulses with few-optical-cycle duration and controlled electric field. Here, we revisit the HHG process driven by 16-TW sub-two-cycle laser pulses to reach high intensity in the 100-eV spectral region and beyond. We show that the combination of above barrier-suppression intensity with a long generation medium significantly enhances the isolation of attosecond pulses compared to lower intensities and/or shorter media and this way reduces the pulse duration as well as field-stability requirements on the laser driver. This novel regime facilitates the real-time observation of electron dynamics at the attosecond timescale in atoms, molecules, and solids.
Sheintop, U., et al. Actively Q-switched tunable narrow bandwidth milli-Joule level Tm:YLF laser. Optics Express 26, 17, 22135–22143 (2018). Publisher's VersionAbstract
A pulsed high energy and narrow bandwidth tunable Tm:YLF laser at the milli-Joule level is demonstrated. The spectral bandwidth was narrowed down to 0.15 nm FWHM, while 33 nm of tunability range between 1873 nm and 1906 nm was achieved using a pair of YAG Etalons. The laser was actively Q-switched using an acousto-optic modulator and mJ level pulse energy was measured along the whole tuning range at a repetition rate of 1 kHz. Up to 1.97 mJ of energy per pulse was achieved at a pulse duration of 37 ns at a wavelength of 1879 nm, corresponding to a peak-power of 53.2 kW and at a slope efficiency of 36 &\#x00025;. The combination of both high energy pulsed lasing and spectral tunability, while maintaining narrow bandwidth across the whole tunability range, enhances the laser abilities, which could enable new applications in the sensing, medical and material processing fields.
Cohen, E., et al. Fast Energy Transfer in CdSe Quantum Dot Layered Structures: Controlling Coupling with Covalent-Bond Organic Linkers. The Journal of Physical Chemistry C (2018). Publisher's VersionAbstract
Quantum dot (QD) solids and arrays hold a great potential for novel applications which are aimed at exploiting quantum properties in room-temperature devices. Careful tailoring of the QD energy levels and coupling between dots could lead to efficient energy-harvesting devices. Here, we used a self-assembly method to create a disordered layered structure of QDs, coupled by covalently bonded organic molecules. Energy transfer rates from small (donor) to large (acceptor) QDs are measured. Best tailoring of the QDs energy levels and the length of the linking molecules results in an energy transfer rate as high as 30 ps–1. Such rates approach energy transfer rates of the highly efficient photosynthesis complexes and are compatible with a coherent mechanism of energy transfer. These results may pave way for new controllable building blocks for future technologies.
Bergues, B., et al. Tabletop nonlinear optics in the 100-eV spectral region. Optica 5, 3, 237–242 (2018). Publisher's VersionAbstract

Nonlinear light&\#x2013;matter interactions in the extreme ultraviolet (XUV) are a prerequisite to perform XUV-pump/XUV-probe spectroscopy of core electrons. Such interactions are now routinely investigated at free-electron laser (FEL) facilities. Yet, electron dynamics are often too fast to be captured with the femtosecond resolution of state-of-the-art FELs. Attosecond pulses from laser-driven XUV-sources offer the necessary temporal resolution. However, intense attosecond pulses supporting nonlinear processes have only been available for photon energy below 50&\#x00A0;eV, precluding XUV-pump/XUV-probe investigation of typical inner-shell processes. Here, we surpass this limitation by demonstrating two-photon absorption from inner electronic shells of xenon at photon energies around 93&\#x00A0;eV and 115&\#x00A0;eV. This advance opens the door for attosecond real-time observation of nonlinear electron dynamics deep inside atoms.

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Komm, P., Sheintop, U., Noach, S. & Marcus, G. 87 fs CEP-stable Cr:ZnSe laser system. Laser Physics 28, 2, 025301 (2018). Publisher's VersionAbstract

A hybrid laser scheme for the generation and amplification of mid-IR ultrashort pulses, with a carrier to envelope stable phase, is presented. Seed mid-IR pulses with picojoule energies are obtained via intrapulse difference frequency generation from an 8 fs Ti:sapphire oscillator. The energy of these seed pulses is then amplified in a multipass Cr:ZnSe laser amplifier to more than a nanojoule/pulse level. The duration of the amplified impulses is measured to be 87 fs, and the width of their spectrum supports their compression to ~50 fs.

2017
Kahn, M. & Marcus, G. Proposal for strong field physics simulation by means of optical waveguide. J. Phys. B: At. Mol. Opt. Phys. 50, 9, 095004 (2017). Publisher's VersionAbstract

Understanding the interaction of atoms and molecules with an intense laser radiation field is key for many applications such as high harmonic generation and attosecond physics. Because of the non-perturbative nature of strong field physics, some simplifications and approximation methods are often used to shed light on these processes. One of the most fruitful approaches to gain an insight into the physics of such interactions is the three-step-model, in which, the electron first tunnels out through the barrier and then propagates classically in the continuum. Despite the great success of this and other more sophisticated models there are still many ambiguities and open questions, e.g. how long it takes for the electron to tunnel through the barrier. Most of them stem from the difficulties in understanding electron trajectories in the classically ‘forbidden’ zone under the barrier. In this theoretical paper we show that strong field physics and the propagation of electromagnetic waves in a curved waveguide are governed by the same Schrödinger equation. We propose to fabricate a curved optical waveguide, and use this isomorphism to mimic strong field physics. Such a simulating system will allow us to directly probe the wave-function at any point, including the ‘tunneling’ zone.

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Rivas, D.E., et al. Next Generation Driver for Attosecond and Laser-plasma Physics. Scientific Reports 7, 1, 5224 (2017). Publisher's VersionAbstract
The observation and manipulation of electron dynamics in matter call for attosecond light pulses, routinely available from high-order harmonic generation driven by few-femtosecond lasers. However, the energy limitation of these lasers supports only weak sources and correspondingly linear attosecond studies. Here we report on an optical parametric synthesizer designed for nonlinear attosecond optics and relativistic laser-plasma physics. This synthesizer uniquely combines ultra-relativistic focused intensities of about 1020 W/cm2 with a pulse duration of sub-two carrier-wave cycles. The coherent combination of two sequentially amplified and complementary spectral ranges yields sub-5-fs pulses with multi-TW peak power. The application of this source allows the generation of a broad spectral continuum at 100-eV photon energy in gases as well as high-order harmonics in relativistic plasmas. Unprecedented spatio-temporal confinement of light now permits the investigation of electric-field-driven electron phenomena in the relativistic regime and ultimately the rise of next-generation intense isolated attosecond sources.
Kahn, M. & Marcus, G. Proposal for strong field physics simulation by means of optical waveguide. J. Phys. B: At. Mol. Opt. Phys. 50, 095004 (2017). Publisher's Version j_phys_b_image_of_the_week.jpg
2016
Gu, X., et al. Few-Cycle Mid-Infrared OPCPA System. Ultrashort Pulse Laser Technology 135–151 (2016). Publisher's Version
Deng, Y., et al. Ultrafast Excitation of an Inner-Shell Electron by Laser-Induced Electron Recollision. Phys. Rev. Lett. 116, 073901 (2016). Publisher's VersionAbstract

Extreme ultraviolet attosecond pulses, generated by a process known as laser-induced electron recollision, are a key ingredient for attosecond metrology, providing a tool to precisely initiate and probe subfemtosecond dynamics in atoms, molecules, and solids. However, extending attosecond metrology to scrutinize the dynamics of the inner-shell electrons is a challenge, that is because of the lower efficiency in generating the required soft x-ray (ω>300eV) attosecond bursts. A way around this problem is to use the recolliding electron to directly initiate the desired inner-shell process, instead of using the currently low flux x-ray attosecond sources. Such an excitation process occurs in a subfemtosecond time scale, and may provide the necessary “pump” step in a pump-probe experiment. Here we used a few cycle infrared (λ01800nm) source and observed direct evidence for inner-shell excitations through the laser-induced electron recollision process. It is the first step toward time-resolved core-hole studies in the keV energy range with subfemtosecond time resolution.

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2015
Deng, Y., et al. Direct evidences for inner-shell electron-excitation by laser induced electron recollision. arxiv 1509.05361 (2015). Publisher's VersionAbstract

Extreme ultraviolet (XUV) attosecond pulses, generated by a process known as laser-induced electron recollision, are a key ingredient for attosecond metrology, providing a tool to precisely initiate and probe sub-femtosecond dynamics in the microcosms of atoms, molecules and solids[1]. However, with the current technology, extending attosecond metrology to scrutinize the dynamics of the inner-shell electrons is a challenge, that is because of the lower efficiency in generating the required soft x-ray \hbar\omega>300 eV attosecond bursts and the lower absorption cross-sections in this spectral range. A way around this problem is to use the recolliding electron to directly initiate the desired inner-shell process, instead of using the currently low flux x-ray attosecond sources.Such an excitation process occurs in a sub-femtosecond timescale, and may provide the necessary "pump" step in a pump-probe experiment[2]. Here we used a few cycle infrared \lambda_{0}~1800nm source[3] and observed direct evidences for inner-shell excitations through the laser-induced electron recollision process. It is the first step toward time-resolved core-hole studies in the keV energy range with sub-femtosecond time resolution.

Rosenthal, N. & Marcus, G. Discriminating between the role of phase matching and that of the single-atom response in resonance plasma-plume high harmonic generation. Phys. Rev. Lett. 115, 133901 (2015). Publisher's VersionAbstract

Resonance enhancement of high-order harmonic generation has recently been found in the interaction of intense ultra-short laser pulses with laser ablated plasma plumes. It is a promising route towards the production of an intense and coherent extreme ultraviolet radiation source. However, the mechanism of this resonance enhancement is still not clear. There are two possible explanations; one relies on a better recombination cross-section through an auto-ionization state in the single-atom response. The other, relies on improved phase matching
conditions around the resonance. Here we try to discriminate between these two conjectures by measuring coherence lengths of the harmonics, both on resonance and off resonance. Our findings support the single-atom response hypothesis.

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Korenfeld, A., et al. High pulse energy passive Q-switching of a diode-pumped Tm:YLF laser by Cr:ZnSe. Laser Physics Letters 12, 045804 (2015). Publisher's VersionAbstract
A passively Q-switched diode-pumped Tm:YLF laser with polycrystalline Cr:ZnSe as the saturable absorber is demonstrated for the first time, to the best of our knowledge. By using saturable absorbers with different initial transmission, the maximum pulse energy reached 4.22 mJ with peak power of 162.3 kW for a pulse duration of 26 ns. The maximum output average power amounted to 2.2 W. These results constitute significant improvement from the highest average power, pulse energy and peak power results for the PQS Tm:YLF laser to date.
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2012
Znakovskaya, I., et al. Subcycle Controlled Charge-Directed Reactivity with Few-Cycle Midinfrared Pulses. Physical Review Letters 108, 6, (2012). Publisher's VersionAbstract
The steering of electron motion in molecules is accessible with waveform-controlled few-cycle laser light and may control the outcome of light-induced chemical reactions. An optical cycle of light, however, is much shorter than the duration of the fastest dissociation reactions, severely limiting the degree of control that can be achieved. To overcome this limitation, we extended the control metrology to the midinfrared studying the prototypical dissociative ionization of D2 at 2.1 μm. Pronounced subcycle control of the directional D+ ion emission from the fragmentation of D2+ is observed, demonstrating unprecedented charge-directed reactivity. Two reaction pathways, showing directional ion emission, could be observed and controlled simultaneously for the first time. Quantum-dynamical calculations elucidate the dissociation channels, their observed phase relation, and the control mechanisms.
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Deng, Y., et al. Carrier-envelope-phase-stable, 1.2mJ, 1.5 cycle laser pulses at 2.1μm. Optics Letters 37, 23, 4973 - 4975 (2012). Publisher's VersionAbstract

We produce 1.5 cycle (10.5 fs), 1.2 mJ, 3 kHz carrier-envelope-phase-stable pulses at 2.1 μm carrier wavelength, from a three-stage optical parametric chirped-pulse amplifier system, pumped by an optically synchronized 1.6 ps Yb:YAG thin disk laser. A chirped periodically poled lithium niobate crystal is used to generate the ultrabroad spectrum needed for a 1.5 cycle pulse through difference frequency mixing of spectrally broadened pulse from a Ti:sapphire amplifier. It will be an ideal tool for producing isolated attosecond pulses with high photon energies.

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Marcus, G., et al. Subfemtosecond K-Shell Excitation with a Few-Cycle Infrared Laser Field. Physical Review Letters 108, 2, 023201 (2012). Publisher's VersionAbstract

Subfemtosecond bursts of extreme ultraviolet radiation, facilitated by a process known as high-order harmonic generation, are a key ingredient for attosecond metrology, providing a tool to precisely initiate and probe ultrafast dynamics in the microcosms of atoms, molecules, and solids. These ultrashort pulses are always, and as a by-product of the way they are generated, accompanied by laser-induced recollisions of electrons with their parent ions. By using a few-cycle infrared (λ0=2.1 μm) driving laser, we were able to directly excite high-energy (∼870 eV) inner-shell electrons through laser-induced electron recollision, opening the door to time-resolved studies of core-level and concomitant multielectron dynamics.

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2010
Dou, T.H., et al. Dispersion control with reflection grisms of an ultra-broadband spectrum approaching a full octave. Optics Express 18, 26, 27900 - 27909 (2010). Publisher's VersionAbstract
We report the design, implementation, and characterization of a grism-pair stretcher in a near-infrared noncollinear optical parametric chirped-pulse amplifier (OPCPA) that is capable of controlling a bandwidth of 440 nm. Our dynamic dispersion control scheme relies on the grism stretcher working in conjunction with an acousto-optic programmable dispersive filter (Dazzler) to jointly compensate large amount of material dispersion. A spectral interference technique is used to characterize the spectral phase of the grism stretcher. This ultra-broadband device opens up the way to generate sub-2-cycle laser pulses.
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2009
Gu, X., et al. Generation of carrier-envelope-phase-stable 2-cycle 740-uJ pulses at 2.1-um carrier wavelength. Optics Express 17, 1, 62 - 69 (2009). Publisher's VersionAbstract
We produce carrier-envelope-phase-stable 15.7-fs (2-cycle) 740-μJ pulses at the 2.1-μm carrier wavelength, from a three-stage optical parametric chirped-pulse amplifier system, pumped by an optically synchronized 49-ps 11-mJ Nd:YLF laser. A novel seed pulse spectral shaping method is used to ascertain the true amplified seed energy and the parametric superfluorescence levels.
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Marcus, G. & Tsori, Y. Phase Separation Transition in Liquids and Polymers Induced by Electric Field Gradients. Journal of the Physical Society of Japan 78, (2009). Publisher's VersionAbstract
Spatially uniform electric fields have been used to induce instabilities in liquids and polymers, and to orient and deform ordered phases of block-copolymers. Here we discuss the demixing phase transition occurring in liquid mixtures when they are subject to spatially nonuniform fields. Above the critical value of potential, a phase-separation transition occurs, and two coexisting phases appear separated by a sharp interface. Analytical and numerical composition profiles are given, and the interface location as a function of charge or voltage is found. The possible influence of demixing on the stability of suspensions and on inter-colloid interaction is discussed. ©2009 The Physical Society of Japan
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