Dr. Hanieh Fattahi

Recent advances in petahertz electric field sampling

Andreas Herbst, Kilian Scheffter, M.M. Bidhendi, M. Kieker, Anchit Srivastava, Hanieh Fattahi

The ability to resolve the complete electric field of laser pulses from terahertz to mid-infrared spectral ranges has enriched time-domain spectroscopy for decades. Field-resolved measurements in this range have been performed routinely in ambient air by various techniques like electro-optic sampling, photoconductive switching, field-induced second harmonic generation, and time stretch photonics. On the contrary, resolving the electric field of light at the near-infrared spectral range has been limited to attosecond streaking and other techniques that require operation in vacuum. Recent advances are circumventing these<br>shortcomings and extending the direct, ambient air field detection of light to petahertz frequencies. In the first part of this letter, recent field-resolved techniques are reviewed. In the second part, different approaches for temporal scanning are discussed, as the temporal resolution of the time-domain methods is prone to temporal jitter. The review concludes by discussing technological obstacles and emerging applications of such advancements.

Efficient nonlinear compression of a thin-disk oscillator to 8.5 fs at 55 W average power

Gaia Barbiero, Haochuang Wang, Martin Grassl, Sebastian Groebmeyer, Dziugas Kimbaras, Marcel Neuhaus, Vladimir Pervak, Thomas Nubbemeyer, Hanieh Fattahi, et al.

We demonstrate an efficient hybrid-scheme for nonlinear pulse compression of high-power thin-disk oscillator pulses to the sub-10 fs regime. The output of a home-built, 16 MHz, 84 W, 220 fs Yb:YAG thin-disk oscillator at 1030 nm is first compressed to 17 fs in two nonlinear multipass cells. In a third stage, based on multiple thin sapphire plates, further compression to 8.5 fs with 55 W output power and an overall optical efficiency of 65% is achieved. Ultrabroadband mid-infrared pulses covering the spectral range 2.4-8 μm were generated from these compressed pulses by intra-pulse difference frequency generation.

Broadband terahertz solid-state emitter driven by Yb:YAG thin-disk oscillator

Gaia Barbiero, Haochuan Wang, Jonathan Brons, Bo-Han Chen, Vladimir Pervak, Hanieh Fattahi

We report on a table-top, high-power, terahertz (THz) solid-state emitter driven by few-cycle near-infrared pulses at 16 MHz repetition rate in gallium phosphide (GaP) crystals. Two external nonlinear multi-pass cells are used to shorten the output of a home-built, 100W, 265 fs, 6.2 mu J Yb:YAG thin-disk oscillator, operating at 1030 nm, to 18 fs with 3.78 mu J pulse energy. The broadband spectrum of the THz driver allowed for the extension of the THz cutoff frequency to 5.7 THz at the dynamic range of 10(4). By employing the high-power Yb:YAG thin-disk oscillator, the low efficiency of the THz generation is circumvented, resulting in the generation of up to 100 mu W, multi-octave THz pulses at 5 THz cutoff frequency in a 2 mm thick GaP crystal.

Multi-octave, CEP-stable source for high-energy field synthesis

Ayman Alismail, Haochuang Wang, Gaia Barbiero, Najd Altwaijry, Syed Ali Hussain, Volodymyr Pervak, Wolfgang Schweinberger, Abdallah M. Azzeer, Ferenc Krausz, et al.

Multi-octave, CEP-stable source for high-energy field synthesis

Ayman Alismail, Haochuang Wang, Gaia Barbiero, Najd Altwaijry, Syed Ali Hussain, Volodymyr Pervak, Wolfgang Schweinberger, Abdallah M. Azzeer, Ferenc Krausz, et al.

The development of high-energy, high-power, multi-octave light transients is currently the subject of intense research driven by emerging applications in attosecond spectroscopy and coherent control. We report on a phase-stable, multi-octave source based on a Yb:YAG amplifier for light transient generation. We demonstrate the amplification of a two-octave spectrum to 25 μJ of energy in two broadband amplification channels and their temporal compression to 6 and 18 fs at 1 and 2 μm, respectively. In this scheme, due to the intrinsic temporal synchronization between the pump and seed pulses, the temporal jitter is restricted to long-term drift. We show that the intrinsic stability of the synthesizer allows subcycle detection of an electric field at 0.15 PHz. The complex electric field of the 0.15-PHz pulses and their free induction decay after interaction with water molecules are resolved by electro-optic sampling over 2 ps. The scheme is scalable in peak and average power.

High Energy, Sub-Cycle, Field Synthesizers

Haochuang Wang, Ayman Alismail, Gaia Barbiero, Raja Naeem Ahmad, Hanieh Fattahi

Tailoring the electromagnetic field transients has been a prominent research focus over the last decade. Advances in ultrashort pulse generation and stabilizing the carrier phase of the electromagnetic field relative to its envelope allowed for extension of coherent synthesis to optical frequencies and ultrashort pulse domain at tens of microjoules of energy. In parallel, ytterbium-doped lasers become a mature technology. They are able to deliver down to 1-picosecond scale pulses at hundreds of millijoule energy and kilowatt-scale average power, making them suitable frontends for scaling the energy and power of light transients. In this paper, we discuss two conceptual schemes, our experimental results, and technological challenges for generation of sub-cycle light transients based on Yb:YAG thin-disk lasers by direct and efficient spectral broadening of ytterbium-doped lasers, and by coherent combination of pulses from multiple broadband optical parametric amplifiers. Moreover, a conceptual design study for a novel synthesis scheme based on polarization splitting of a broadband spectrum and amplification of each polarization in a separate stage is presented. The novel sources hold promise for studying and controlling the nonlinear interactions of matter with custom-tailored light transients at a sub-cycle period of their electric field, opening up unprecedented opportunities in attoscience and strong-field physics.

High Energy, Sub-Cycle, Field Synthesizers

Haochuang Wang, Ayman Alismail, Gaia Barbiero, Raja Naeem Ahmad, Hanieh Fattahi

Theoretical Study: High Harmonic Generation by Light Transients

Maximilian Wendl, Maximilian Högner, Hanieh Fattahi

The dynamic of electron densities in matter upon the interaction with an intense, few-cycle electric field of light causes variety of nonlinear phenomena. Capturing the spatiotemporal dynamics of electrons calls for isolated attosecond pulses in the X-ray regime, with sufficient flux to allow for: (i) attosecond pump–attosecond probe spectroscopy; or (ii) four-dimensional imaging. Light field synthesizers generate arbitrary sub-cycle, non-sinusoidal waveforms. They have a great potential to overcome the limitations of current laser sources and to extend attosecond pulses towards the X-ray regime. In this paper, we show theoretically how the achievable high-energy, high-power waveforms from current light field synthesizers can be optimized to enhance the harmonic yield at high photon energies and can serve as a promising source for scaling the photon energies of attosecond pulses. We demonstrate that the simulated optimized, non-sinusoidal waveform in this work can increase the photon flux of keV, attosecond pulses by five orders of magnitude compared to the achievable flux from longer wavelength sources and at similar photon energies.

Theoretical Study: High Harmonic Generation by Light Transients

Maximilian Wendl, Maximilian Högner, Hanieh Fattahi

Prospects of third-generation femtosecond laser technology in biological spectromicroscopy

Hanieh Fattahi, Zohreh Fattahi, Asghar Ghorbani

The next generation of biological imaging modalities will be a movement towards super-resolution, label-free approaches to realize subcellular images in a nonperturbative, non-invasive manner and towards new detection metrologies to reach a higher sensitivity and dynamic range. In this paper, we discuss how the third generation femtosecond laser technology in combination with the already existing concepts in time-resolved spectroscopy could fulfill the requirements of these exciting prospects. The expected enhanced specificity and sensitivity of the envisioned super-resolution microscope could lead us to a better understanding of the inter- and intra-cellular molecular transport and DNA-protein interaction.

Prospects of third-generation femtosecond laser technology in biological spectromicroscopy

Hanieh Fattahi, Zohreh Fattahi, Asghar Ghorbani

20 mJ, 1 ps Yb: YAG Thin-disk Regenerative Amplifier

Ayman Alismail, Haochuang Wang, Jonathan Brons, Hanieh Fattahi

This is a report on a 100 W, 20 mJ, 1 ps Yb:YAG thin-disk regenerative amplifier. A homemade Yb:YAG thin-disk, Kerr-lens mode-locked oscillator with turn-key performance and microjoule-level pulse energy is used to seed the regenerative chirped-pulse amplifier. The amplifier is placed in airtight housing. It operates at room temperature and exhibits stable operation at a 5 kHz repetition rate, with a pulse-to-pulse stability less than 1%. By employing a 1.5 mm-thick beta barium borate crystal, the frequency of the laser output is doubled to 515 nm, with an average power of 70 W, which corresponds to an optical-to-optical efficiency of 70%. This superior performance makes the system an attractive pump source for optical parametric chirped-pulse amplifiers in the near-infrared and mid-infrared spectral range. Combining the turn-key performance and the superior stability of the regenerative amplifier, the system facilitates the generation of a broadband, CEP-stable seed. Providing the seed and pump of the optical parametric chirped-pulse amplification (OPCPA) from one laser source eliminates the demand of active temporal synchronization between these pulses. This work presents a detailed guide to set up and operate a Yb:YAG thin-disk regenerative amplifier, based on chirped-pulse amplification (CPA), as a pump source for an optical parametric chirped-pulse amplifier.

20 mJ, 1 ps Yb: YAG Thin-disk Regenerative Amplifier

Ayman Alismail, Haochuang Wang, Jonathan Brons, Hanieh Fattahi

Cross-polarized, multi-octave supercontinuum generation

Haochuang Wang, Ayman Alismail, Gaia Barbiero, Maximilian Wendl, Hanieh Fattahi

Cross-polarized, multi-octave supercontinuum generation

Haochuang Wang, Ayman Alismail, Gaia Barbiero, Maximilian Wendl, Hanieh Fattahi

The generation of superoctave spectra from the interaction of intense ultrashort optical pulses and cubic nonlinearity is the result of interplay between the dispersion and nonlinearity of a material and various propagation effects. The cubic nonlinearity can be enhanced when it is combined with a quadratic-cascaded nonlinearity, relaxing the requirement on the laser’s peak intensity for supercontinuum (SC) generation. In this Letter, we demonstrate and compare the generation of an SC driven from cubic and cascaded quadratic nonlinearities at an anomalous and zero dispersion wavelength (ZDW). We show the filament-free SC generation of femtosecond mid-infrared pulses by harvesting cascaded quadratic nonlinearity and, at ZDW, requires a lower threshold peak intensity and results in a higher power spectral density for the newly generated spectral components. The presented method is a suitable approach for generating multi-octave spectra from low peak-power, high average-power oscillators or a suitable seed for optical parametric amplifiers and multi-octave field synthesizers.

Carrier-envelope phase stable, 5.4 μJ, broadband, mid-infrared pulse generation from a 1-ps, Yb:YAG thin-disk laser

Ayman Alismail, Haochuan Wang, Najd Altwaijry, Hanieh Fattahi

We report on a simple scheme to generate broadband, μJ pulses centered at 2.1 μm with an intrinsic carrier-envelope phase (CEP) stability from the output of a Yb:YAG regenerative amplifier delivering 1-ps pulses with randomly varying CEP. To the best of our knowledge, the reported system has the highest optical-to-optical efficiency for converting 1-ps, 1 μm pulses to CEP stable, broadband, 2.1 μm pulses. The generated coherent light carries an energy of 5.4 μJ, at 5 kHz repetition rate, that can be scaled to higher energy or power by using a suitable front end, if required. The system is ideally suited for seeding broadband parametric amplifiers and multichannel synthesizers pumped by picosecond Yb-doped amplifiers, obviating the need for active timing synchronization. Alternatively, this scheme can be combined with high-power oscillators with tens of μJ energy to generate CEP stable, multioctave supercontinua, suitable for field-resolved and time-resolved spectroscopy.

Carrier-envelope phase stable, 5.4 μJ, broadband, mid-infrared pulse generation from a 1-ps, Yb:YAG thin-disk laser

Ayman Alismail, Haochuan Wang, Najd Altwaijry, Hanieh Fattahi

Nonlinear optics: Attosecond nanophotonics

Giulio Vampa, Hanieh Fattahi, Jelena Vuckovic, Ferenc Krausz

Nonlinear optics: Attosecond nanophotonics

Giulio Vampa, Hanieh Fattahi, Jelena Vuckovic, Ferenc Krausz

Combining attosecond science and nanophotonics potentially offers a route to enhance control over light-matter interactions at the nanoscale and provide a promising platform for information processing.

1 kW, 200 mJ picosecond thin-disk laser system

Thomas Nubbemeyer, Martin Kaumanns, Moritz Ueffing, Martin Gorjan, Ayman Alismail, Hanieh Fattahi, Jonathan Brons, Oleg Pronin, Helena G. Barros, et al.

1 kW, 200 mJ picosecond thin-disk laser system

Thomas Nubbemeyer, Martin Kaumanns, Moritz Ueffing, Martin Gorjan, Ayman Alismail, Hanieh Fattahi, Jonathan Brons, Oleg Pronin, Helena G. Barros, et al.

We report on a laser system based on thin-disk technology and chirped pulse amplification, providing output pulse energies of 200 mJ at a 5 kHz repetition rate. The amplifier contains a ring-type cavity and two thin Yb:YAG disks, each pumped by diode laser systems providing up to 3.5 kW power at a 969 nm wavelength. The average output power of more than 1 kW is delivered in an excellent output beam characterized by M2=1.1. The output pulses are compressed to 1.1 ps at full power with a pair of dielectric gratings.

Near-PHz-bandwidth, phase-stable continua generated from a Yb:YAG thin-disk amplifier

Hanieh Fattahi, Haochuan Wang, Ayman Alismail, Gunnar Arisholm, Vladimir Pervak, Abdallah M. Azzeer, Ferenc Krausz

We report on the generation of a multi-octave, phase-stable continuum from the output of a Yb:YAG regenerative amplifier delivering 1-ps pulses with randomly varying carrier-envelope phase (CEP). The intrinsically CEP-stable spectral continuum spans from 450 nm to beyond 2500 nm, covering a spectral range of about 0.6 PHz. The generated coherent broadband light carries an energy of 4 mu J, which can be scaled to higher values if required. The system has been designed and is ideally suited for seeding broadband parametric amplifiers and multi-channel synthesizers pumped by picosecond Yb: YAG amplifiers, obviating the need for active timing synchronization required in previous approaches. The presented concept paves the way to cost-effective, reliable all-Yb:YAG single-cycle sources with terawatt peak-power and tens-of-Watts average power.

Sub-cycle light transients for attosecond, X-ray, four-dimensional imaging

Hanieh Fattahi

This paper reviews the revolutionary development of ultra-short, multi-TW laser pulse generation made possible by current laser technology. The design of the unified laser architecture discussed in this paper, based on the synthesis of ultrabroadband optical parametric chirped-pulse amplifiers, promises to provide powerful light transients with electromagnetic forces engineerable on the electron time scale. By coherent combination of multiple amplifiers operating in different wavelength ranges, pulses with wavelength spectra extending from less than 1 μm to more than 10 μm, with sub-cycle duration at unprecedented peak and average power levels can be generated. It is shown theoretically that these light transients enable the efficient generation of attosecond X-ray pulses with photon flux sufficient to image, for the first time, picometre-attosecond trajectories of electrons, by means of X-ray diffraction and record the electron dynamics by attosecond spectroscopy. The proposed system leads to a tool with sub-atomic spatio-temporal resolution for studying different processes deep inside matter.

Sub-cycle light transients for attosecond, X-ray, four-dimensional imaging

Hanieh Fattahi

Yb:YAG-Pumped, Few-Cycle Optical Parametric Amplifiers

Hanieh Fattahi

In this chapter, the principle, design, and characteristics of high-efficiency, short-pulse-pumped, few-cycle optical parametric chirped-pulse amplification (OPCPA) systems are reviewed. To this end, the feasibility of two techniques to increase the conversion efficiency of few-cycle OPCPA systems is demonstrated and discussed. The techniques result in 2.5 mJ, 7.5 W pulses and correspond to a pump-to-signal conversion efficiency of 30%. The broadband amplified spectrum supports 5.7 fs. Finally, the feasibility of extending the amplified spectrum to a near-single-cycle regime by using the combination of different crystals and phase matching is shown.

Broadband beamsplitter for high intensity laser applications in the infra-red spectral range

Tatiana Amotchkina, Hanieh Fattahi, Yurij. A. Pervak, Michael Trubetskov, Vladimir Pervak

We report on design, production and characterization of an extremely broadband multilayer beamsplitter, covering wavelength range from 0.67 - 2.6 mu m. The group delay dispersion has small oscillations in the above mentioned working range. We used a new algorithm with floating constants allowing us to obtain a smooth and near constant GDD. The optical element based on the beamsplitter is used for dividing a low-energy super-octave spectrum into several sub-spectral regions which are later amplified and coherently combined.

Attosecond nonlinear polarization and light-matter energy transfer in solids

Annkatrin Sommer, Elisabeth Bothschafter, S. A. Sato, Clemens Jakubeit, Tobias Latka, Olga Razskazovskaya, Hanieh Fattahi, Michael Jobst, Hans Wolfgang Schweinberger, et al.

Electric-field-induced charge separation (polarization) is the most fundamental manifestation of the interaction of light with matter and a phenomenon of great technological relevance. Nonlinear optical polarization produces coherent radiation in spectral ranges inaccessible by lasers and constitutes the key to ultimate-speed signal manipulation. Terahertz techniques have provided experimental access to this important observable up to frequencies of several terahertz. Here we demonstrate that attosecond metrology extends the resolution to petahertz frequencies of visible light. Attosecond polarization spectroscopy allows measurement of the response of the electronic system of silica to strong (more than one volt per ångström) few-cycle optical (about 750 nanometres) fields. Our proof-of-concept study provides time-resolved insight into the attosecond nonlinear polarization and the light–matter energy transfer dynamics behind the optical Kerr effect and multi-photon absorption. Timing the nonlinear polarization relative to the driving laser electric field with sub-30-attosecond accuracy yields direct quantitative access to both the reversible and irreversible energy exchange between visible–infrared light and electrons. Quantitative determination of dissipation within a signal manipulation cycle of only a few femtoseconds duration (by measurement and ab initio calculation) reveals the feasibility of dielectric optical switching at clock rates above 100 terahertz. The observed sub-femtosecond rise of energy transfer from the field to the material (for a peak electric field strength exceeding 2.5 volts per ångström) in turn indicates the viability of petahertz-bandwidth metrology with a solid-state device.

Attosecond nonlinear polarization and light-matter energy transfer in solids

Annkatrin Sommer, Elisabeth Bothschafter, S. A. Sato, Clemens Jakubeit, Tobias Latka, Olga Razskazovskaya, Hanieh Fattahi, Michael Jobst, Hans Wolfgang Schweinberger, et al.

Self-compressed, spectral broadening of a Yb:YAG thin-disk amplifier

Theresa Buberl, Ayman Alismail, Haochuang Wang, Nicholas Karpowicz, Hanieh Fattahi

We demonstrate pulse shortening of 1-ps Yb:YAG thin-disk regenerative amplifier to 500 fs by cross-polarized wave generation (XPW) in a 6 mm BaF2 crystal. The process is self-compressed and has 8.5% conversion efficiency corresponding to 18 µJ energy. Our theoretical and experimental investigation shows that the factor of 3−−√ spectral broadening and pulse shortening in ps-XPW-generation only happens in unsaturated regime. We demonstrate that the initial spectral chirp affects the spectral broadening and pulse shortening of XPW pulses.

Self-compressed, spectral broadening of a Yb:YAG thin-disk amplifier

Theresa Buberl, Ayman Alismail, Haochuang Wang, Nicholas Karpowicz, Hanieh Fattahi

High-power, 1-ps, all-Yb:YAG thin-disk regenerative amplifier

Hanieh Fattahi, Ayman Alismail, Haochuang Wang, Jonathan Brons, Oleg Pronin, Theresa Buberl, Lenard Vamos, Gunnar Arisholm, Abdallah M. Azzeer, et al.

We report a 100 W, 20 mJ, 1-ps, all-Yb:YAG thin-disk regenerative amplifier seeded by a microjoule-level Yb:YAG thin-disk Kerr-lens mode-locked oscillator. The regenerative amplifier is implemented in a chirped pulse amplification system and operates at an ambient temperature in air, delivering ultrastable output pulses at a 5 kHz repetition rate and with a root mean square power noise value of less than 0.5%. Second harmonic generation of the amplifier’s output in a 1.5 mm-thick BBO crystal results in more than 70 W at 515 nm, making the system an attractive source for pumping optical parametric chirped pulse amplifiers in the visible and near-infrared spectral ranges.

High-power, 1-ps, all-Yb:YAG thin-disk regenerative amplifier

Hanieh Fattahi, Ayman Alismail, Haochuang Wang, Jonathan Brons, Oleg Pronin, Theresa Buberl, Lenard Vamos, Gunnar Arisholm, Abdallah M. Azzeer, et al.

Third-Generation Femtosecond Technology

Hanieh Fattahi, Ferenc Krausz

Third-Generation Femtosecond Technology

Hanieh Fattahi, Ferenc Krausz

This thesis offers a thorough and informative study of high-power, high-energy optical parametric chirped pulse amplifications systems, the foundation of the next generation of femtosecond laser technology. Starting from the basics of the linear processes involved and the essential design considerations, the author clearly and systematically describes the various prerequisites of the nonlinear optical systems expected to drive attosecond physics in the coming decade. In this context, he gives an overview of methods for generating the broadband and carrier-envelope-phase stable seed pulses necessary for producing controlled electric-field waveforms in the final system; provides a guide to handling the high-power, high-energy pump lasers required to boost the pulse energy to the desired operating range; describes the design of the nonlinear optical system used to perform the amplification, including modes of operation for ultra-broadband infrared-visible pulses or narrowband (yet still ultrafast) pulses tunable over multiple octaves; and finally presents a prospective high-energy field synthesizer based upon these techniques. As such, this work is essential reading for all scientists interested in utilizing the newest generation of ultrafast systems.

Decoupling chaotic amplification and nonlinear phase in high-energy thin-disk amplifiers for stable OPCPA pumping

Hanieh Fattahi, Alexander Schwarz, Xiao Tao Geng, Sabine Keiber, Dong Eon Kim, Ferenc Krausz, Nicholas Karpowicz

Decoupling chaotic amplification and nonlinear phase in high-energy thin-disk amplifiers for stable OPCPA pumping

Hanieh Fattahi, Alexander Schwarz, Xiao Tao Geng, Sabine Keiber, Dong Eon Kim, Ferenc Krausz, Nicholas Karpowicz

The dynamics of chirped pulse amplification in thin-disk regenerative amplifiers relevant to the pumping of optical parametric chirp pulse amplification systems are described. It is shown that the suitability for reproducible pumping of subsequent nonlinear processes requires a balance between the demands of avoiding chaotic pulse train dynamics and<br>providing a reproducible spectral phase. We describe measures that may be taken to ensure that a laser system operates in the desired stable regime.

Third-generation femtosecond technology

Hanieh Fattahi, Helena G. Barros, Martin Gorjan, Thomas Nubbemeyer, Bidoor Alsaif, Catherine Y. Teisset, Marcel Schultze, Stephan Prinz, Matthias Haefner, et al.

Third-generation femtosecond technology

Hanieh Fattahi, Helena G. Barros, Martin Gorjan, Thomas Nubbemeyer, Bidoor Alsaif, Catherine Y. Teisset, Marcel Schultze, Stephan Prinz, Matthias Haefner, et al.

Femtosecond pulse generation was pioneered four decades ago using mode-locked dye lasers, which dominated the field for the following 20 years. Dye lasers were then replaced with titanium-doped sapphire (Ti:Sa) lasers, which have had their own two-decade reign. Broadband optical parametric amplifiers (OPAs) appeared on the horizon more than 20 years ago but have been lacking powerful, cost-effective picosecond pump sources for a long time. Diode-pumped ytterbium-doped solid-state lasers are about to change this state of affairs profoundly. They are able to deliver 1 ps scale pulses at kilowatt-scale average power levels, which, in thin-disk lasers, may come in combination with terawatt-scale peak powers. Broadband OPAs pumped by these sources hold promise for surpassing the performance of current femtosecond systems so dramatically as to justify referring to them as the next generation. Third-generation femtosecond technology (3FST) offers the potential for femtosecond light tunable over several octaves, multi-terawatt few-cycle pulses, and synthesized multi-octave light transients. Unique tunability, temporal confinement, and waveform variety in combination with unprecedented average powers will extend nonlinear optics and laser spectroscopy to previously inaccessible wavelength domains, ranging from the far IR to the x-ray regime. Here we review the underlying concepts, technologies, and proof-of-principle experiments. A conceptual design study of a prototypical tunable and wideband source demonstrates the potential of 3FST for pushing the frontiers of femtosecond and attosecond science.

Efficient, octave-spanning difference-frequency generation using few-cycle pulses in simple collinear geometry

Hanieh Fattahi, Alexander Schwarz, Sabine Keiber, Nicholas Karpowicz

We present experimental observations and corresponding numerical simulations illustrating the difference-frequency generation of mid-infrared radiation using few-cycle near-infrared-to-visible pulses, which yields conversion efficiencies above 12% in beta-barium borate crystal. Type I and type II phase-matching are shown to yield qualitatively different intensity-scaling behavior, with the former showing higher overall efficiency, especially with the addition of a zero-order wave plate for modifying the polarization state of the pulse, and the latter having a better stability of the spectrum versus input intensity.

Efficient, octave-spanning difference-frequency generation using few-cycle pulses in simple collinear geometry

Hanieh Fattahi, Alexander Schwarz, Sabine Keiber, Nicholas Karpowicz

In-Vitro Thermal Study of Different Tips in Various Operating Modes of the Sina Phacoemulsification System

Radin Tahvildari, Hanieh Fattahi, Ahmad Amjadi

Carrier-envelope-phase-stable, 1.2 mJ, 1.5 cycle laser pulses at 2.1 mu m

Yunpei Deng, Alexander Schwarz, Hanieh Fattahi, Moritz Ueffing, Xun Gu, Marcus Ossiander, Thomas Metzger, Volodymyr Pervak, Hideki Ishizuki, et al.

Carrier-envelope-phase-stable, 1.2 mJ, 1.5 cycle laser pulses at 2.1 mu m

Yunpei Deng, Alexander Schwarz, Hanieh Fattahi, Moritz Ueffing, Xun Gu, Marcus Ossiander, Thomas Metzger, Volodymyr Pervak, Hideki Ishizuki, et al.

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.

Pump-seed synchronization for MHz repetition rate, high-power optical parametric chirped pulse amplification

Hanieh Fattahi, Catherine Y. Teisset, Oleg Pronin, Atsushi Sugita, Roswitha Graf, Vladimir Pervak, Xun Gu, Thomas Metzger, Zsuzsanna Major, et al.

We report on an active synchronization between two independent mode-locked lasers using a combined electronic-optical feedback. With this scheme, seed pulses at MHz repetition rate were amplified in a non-collinear optical parametric chirped pulse amplifier (OPCPA). The amplifier was seeded with stretched 1.5 nJ pulses from a femtosecond Ti:Sapphire oscillator, while pumped with the 1 ps, 2.9 µJ frequency-doubled output of an Yb:YAG thin-disk oscillator. The residual timing jitter between the two oscillators was suppressed to 120 fs (RMS), allowing for an efficient and broadband amplification at 11.5 MHz to a pulse energy of 700 nJ and an average power of 8 W. First compression experiment with 240 nJ amplified pulse energy resulted in a pulse duration of ~10 fs.

Pump-seed synchronization for MHz repetition rate, high-power optical parametric chirped pulse amplification

Hanieh Fattahi, Catherine Y. Teisset, Oleg Pronin, Atsushi Sugita, Roswitha Graf, Vladimir Pervak, Xun Gu, Thomas Metzger, Zsuzsanna Major, et al.

Active stabilization for optically synchronized optical parametric chirped pulse amplification

Alexander Schwarz, Moritz Ueffing, Yunpei Deng, Xun Gu, Hanieh Fattahi, Thomas Metzger, Marcus Ossiander, Ferenc Krausz, Reinhard Kienberger

Active stabilization for optically synchronized optical parametric chirped pulse amplification

Alexander Schwarz, Moritz Ueffing, Yunpei Deng, Xun Gu, Hanieh Fattahi, Thomas Metzger, Marcus Ossiander, Ferenc Krausz, Reinhard Kienberger

The development of new high power laser sources tends toward optical parametric chirped pulse amplification (OPCPA) in recent years. One of the difficulties in OPCPA is the the temporal overlap between pump and seed pulses. In this work we characterize our timing jitter on a single-shot basis using spectrally resolved cross-correlation in combination with a position sensitive detector. A commercial beam stabilization is adapted to actively enhance temporal overlap. This delay-stabilizer reduces the RMS jitter from σ = 127fs down to σ = 24fs. The enhanced temporal overlap is demonstrated in our frontend and we propose the scheme to be applicable in many optically synchronized high-repetition-rate OPCPA systems.

Thermal analysis of different tips for various operating modes of phacoemulsification system

Radin Tahvildari, Hanieh Fattahi, Ahmad Amjadi

Cataract is an opacity that develops in the crystalline lens of the eye, due to alteration in some of its protein fibers, with the consequent impairment of visual acu-ity. The most effective and common treatment is to surgically remove the cloudy lens. In this process the crystalline lens are removed and the eye’s refraction power is restored by inserting an artificial lens. Pha- coemulsification refers to modern cataract surgery in which the eye’s internal lens is emulsified with an ultrasonic hand piece, and aspirated from the eye. Aspirated fluids are replaced with irrigation of bal-anced salt solution, thus maintaining the anterior chamber, as well as cooling the hand piece. The pa-tient can be released soon after the operation. The problem of this procedure in some cases is thermal damage. This research addresses the aforementioned problem through an important parameter, different operating modes of the system. The proposed in-vitro approach has been investigated in details.