Soliton-based pump-seed synchronization for few-cycle OPCPA

Highly stable sub-nanosecond Nd:YAG pump laser for optically synchronized optical parametric chirped-pulse amplification

We developed an optically synchronized highly stable frequency-doubled Nd:YAG laser with sub-nanosecond pulse duration. The 1064 nm seed pulses generated by soliton self-frequency shift in a photonic crystal fiber from Ti:sapphire oscillator pulses were stabilized by controlling input pulse polarization. The seed pulses were amplified to 200 mJ by diode-pumped amplifiers with a high stability of only <0.2% (rms). With an external LBO doubler, the system generated 330 ps green pulse energy of 130 mJ at 532 nm with a conversion efficiency of 65%. The pulse duration was further extended to 490 ps by adjusting Nd:YAG crystal temperature. To the best of our knowledge, these results present a longer pulse duration with higher stability than previous Nd:YAG lasers with sub-nanosecond optical synchronization.

Generation of optically synchronized pump-signal beams for ultrafast OPCPA via the optical Kerr effect

In recent years, multi-petawatt laser installations have achieved unprecedented peak powers, opening new horizons to laser-matter interaction studies. Ultra-broadband and extreme temporal contrast pulse requirements make optical parametric chirped pulse amplification (OPCPA) in the few-picosecond regime the key technology in these systems. To guarantee high fidelity output, however, OPCPA requires excellent synchronization between pump and signal pulses. Here, we propose a new highly versatile architecture for the generation of optically synchronized pump-signal pairs based on the Kerr shutter effect. We obtained >550µJ pump pulses of 12 ps duration at 532 nm optically synchronized with a typical ultrashort CPA source at 800 nm. As a proof-of-principle demonstration, our system was also used for amplification of ∼20µJ ultra-broadband pulses based on an OPCPA setup.

Watt-level all-fiber optical parametric chirped-pulse amplifier working at 1300 nm

We report watt-level average output power near 1300 nm from an all-fiber ultrafast optical parametric chirped-pulse amplifier. A compressed output pulse duration of ∼300  fs is achieved. Multiphoton imaging of a variety of samples carried out with this light source shows a good signal-to-noise ratio. With the demonstrated imaging capability, we believe that this high-power ultrafast laser source addresses a key need in deep tissue multiphoton microscopy.

Thin-disk pumped optical parametric chirped pulse amplifier delivering CEP-stable multi-mJ few-cycle pulses at 6 kHz

We present an optical parametric chirped pulse amplifier (OPCPA) delivering CEP-stable ultrashort pulses with 7 fs, high energies of more than 1.8 mJ and high average output power exceeding 10 W at a repetition rate of 6 kHz. The system is pumped by a picosecond regenerative thin-disk amplifier and exhibits an excellent long-term stability. In a proof-of-principle experiment, high harmonic generation is demonstrated in neon up to the 61^st order.

Next Generation Driver for Attosecond and Laser-plasma Physics

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.

CEP-stable, sub-6 fs, 300-kHz OPCPA system with more than 15 W of average power

We report on a CEP-stable OPCPA system reaching multi-GW peak powers at 300 kHz repetition rate. It delivers 15 W of average power, over 50 µJ of compressed pulse energy and a pulse duration below 6 fs. By implementing an additional pump-seed-synchronization, the output parameters are stabilized over hours with power fluctuations of less than 1.5%.

Pulse synchronization system for picosecond pulse-pumped OPCPA with femtosecond-level relative timing jitter

A simple and compact scheme for synchronization of the pump and signal pulses for short-pulse OPCPA is demonstrated. Relative timing jitter of 17 fs RMS is achieved (1% of the pump pulse duration) and the system remains locked for hours. The scheme uses a balanced optical cross correlator to detect relative delays between the pump and signal pulses and can be operated with just 10's of μJ of pump energy and pJ-level signal energies.

Flat-top picosecond pulses generated by chirped spectral modulation from a Nd:YLF regenerative amplifier for pumping few-cycle optical parametric amplifiers

In this paper we present an optically synchronized Nd:YLF regenerative amplifier optimized for use as a preamplifier in a few-cycle optical parametric chirped pulse amplification pump laser. In the pump amplification process we employ a combination of spectral modulation and chirping in order to control and optimize the temporal shape of the pulses. We report on a comparative study of two methods for generating near-flat-top or custom real-time variable-shaped pump pulses using either controlled chirp and shaping of the spectrum of the pulses seeding a regenerative amplifier or intracavity spectral filtering to broaden the gain bandwidth of the system. We show that in addition to minimizing gain narrowing and B-integral, the efficiency of the cascaded nonlinear processes of the parametric amplifiers can be increased.

Long-term stable passive synchronization between two-color mode-locked lasers with the aid of temperature stabilization

We demonstrate long-term stable passive synchronization between two-color Ti:sapphire (master) and Yb-doped fiber (slave) mode-locked lasers in the master-slave configuration. Active temperature stabilization suppresses the repetition fluctuation of the slave laser, and with the aid of temperature stabilization in combination with simple repetition locking of the master laser, long-term stable synchronization as long as 6 h was realized. The repetition rates of both lasers are locked in submillihertz precision. A timing jitter of 0.75 fs was obtained at a detection bandwidth of 350 kHz.

Table top TW-class OPCPA system driven by tandem femtosecond Yb:KGW and picosecond Nd:YAG lasers

We present a compact TW-class OPCPA system operating at 800 nm. Broadband seed pulses are generated and pre-amplified to 25 μJ in a white light continuum seeded femtosecond NOPA. Amplification of the seed pulses to 35 mJ at a repetition rate of 10 Hz and compression to 9 fs is demonstrated.

Mid-infrared optical parametric amplifier based on a LGSe crystal and pumped at 1.6 μm

We demonstrate the generation of 22.6 μJ of combined energy at 3 μm for sub-300fs pulses at a repetition rate of 1 kHz using a LGSe optical parametric amplifier (OPA). The LGSe OPA is pumped by the 140-fs 1.6 μm pulses from a 300-mW KTA optical parametric chirped pulse amplifier (OPCPA) based on an all-optical synchronization scheme. By using a highly-nonlinear fiber, the output of an erbium-doped fiber laser operating at 1560 nm is shifted to 1050 nm in order to coherently seed a Nd:YLF regenerative amplifier. The LGSe OPA is seeded using the MIR coming from the amplification of the 1.6 μm in the OPCPA.

Broadly wavelength- and pulse width-tunable high-repetition rate light pulses from soliton self-frequency shifting photonic crystal fiber integrated with a frequency doubling crystal

Soliton self-frequency shift (SSFS) in a photonic crystal fiber (PCF) pumped by a long-cavity mode-locked Cr:forsterite laser is integrated with second harmonic generation (SHG) in a nonlinear crystal to generate ultrashort light pulses tunable within the range of wavelengths from 680 to 1800 nm at a repetition rate of 20 MHz. The pulse width of the second harmonic output is tuned from 70 to 600 fs by varying the thickness of the nonlinear crystal, beam-focusing geometry, and the wavelength of the soliton PCF output. Wavelength-tunable pulses generated through a combination of SSFS and SHG are ideally suited for coherent Raman microspectroscopy at high repetition rates, as verified by experiments on synthetic diamond and polystyrene films.

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

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.

Experimental and theoretical investigation of timing jitter inside a stretcher-compressor setup

In an optically synchronized short-pulse optical-parametric chirped-pulse amplification (OPCPA) system, we observe a few-100 fs-scale timing jitter. With an active timing stabilization system slow fluctuations are removed and the timing jitter can be reduced to 100 fs standard deviation (Std). As the main source for the timing fluctuations we could identify air turbulence in the stretcher-compressor setup inside the chirped pulse amplification (CPA) pump chain. This observation is supported by theoretical investigation of group delay changes for angular deviations occurring between the parallel gratings of a compressor or stretcher, as they can be introduced by air turbulence.

Femtosecond Yb:KGW MOPA driven broadband NOPA as a frontend for TW few-cycle pulse systems

White light continuum seeded noncollinear optical parametric amplifier driven by Yb:KGW master oscillator power amplifier (MOPA) system is reported. The demonstrated design provides amplification of broadband pulses at 800 nm up to 20 µJ energy at 1 kHz repetition rate and can be used as simple and reliable frontend source for systems producing high intensity few-cycle pulses. The amplified spectral bandwidth allows for <7 fs pulse durations and preliminary compression of partial spectrum yields sub-10 fs pulse.

Long-term stable passive synchronization of 50 µJ femtosecond Yb-doped fiber chirped-pulse amplifier with a mode-locked Ti:sapphire laser

We report long-term stable passive synchronization of a femtosecond Yb-doped fiber chirped-pulse amplifier (CPA) with a mode-locked Ti:sapphire laser for pump-seed synchronization of an optical parametric chirped-pulse amplification (OPCPA) system. The fiber CPA system delivers pulses with a wavelength of 1035 nm, energy of 50 µJ, and duration of 690 fs at a repetition rate of 0.4 MHz. The seed fiber oscillator is passively synchronized with a mode-locked Ti:sapphire laser by injection of the Ti:sapphire laser pulses into the cavity of the fiber oscillator. The second harmonic (SH) output with a wavelength of 518 nm, energy of 18 µJ, and duration of 1.2 ps was prepared for the OPCPA pump. The measured timing jitter between the pump (fiber SH) and the seed (Ti:sapphire) was 42 ± 14 fs, while the jitter between two oscillator outputs was 1.4 ± 0.5 fs. The robust synchronization technique allows long-term stable operation over 8 h.

Frequency-tunable multigigawatt sub-half-cycle light pulses from coupled-state dynamics of optical solitons and impulsively driven molecular vibrations

Coupling ultrashort optical field waveforms to ultrafast molecular vibrations in an impulsively excited Raman medium is shown to enable the generation of frequency-tunable sub-half-cycle multigigawatt light pulses. In a gas-filled hollow waveguide, this coupled-state dynamics is strongly assisted by soliton effects, which help to suppress temporal stretching of subcycle optical pulses, providing efficient Raman-type impulsive excitation of ultrafast molecular vibrations over large propagation paths.

High average and peak power few-cycle laser pulses delivered by fiber pumped OPCPA system

We report on a high power optical parametric amplifier delivering 8 fs pulses with 6 GW peak power. The system is pumped by a fiber amplifier and operated at 96 kHz repetition rate. The average output power is as high as 6.7 W, which is the highest average power few-cycle pulse laser reported so far. When stabilizing the seed oscillator, the system delivered carrier-envelop phase stable laser pulses. Furthermore, high harmonic generation up to the 33(th) order (21.8 nm) is demonstrated in a Krypton gas jet. In addition, the scalability of the presented laser system is discussed.

Fiber-amplifier pumped high average power few-cycle pulse non-collinear OPCPA

We report on the performance of a 60 kHz repetition rate sub-10 fs, optical parametric chirped pulse amplifier system with 2 W average power and 3 GW peak power. This is to our knowledge the highest average power sub-10 fs kHz-amplifier system reported to date. The amplifier is conceived for applications at free electron laser facilities and is designed such to be scalable in energy and repetition rate.

Few-cycle OPCPA system at 143 kHz with more than 1 microJ of pulse energy

We present an OPCPA system delivering 8.8 fs (3.3 optical cycles) pulses with 1.3 microJ of energy at 143 kHz repetition rate. Pump and seed for the parametric amplification are simultaneously generated by a broadband Ti:sapphire oscillator. The spectral components beyond 1000 nm are separated and amplified in an Yb:YAG thin-disk regenerative amplifier. The pulses are characterized using autocorrelation and SPIDER apparatus. With a pulse peak power of nearly 130 MW, the system is well-suited for future table top strong field experiments.

Compact fiber amplifier pumped OPCPA system delivering Gigawatt peak power 35 fs pulses

We report on a compact Gigawatt peak power OPCPA system which is pumped by the second harmonic of an Yb-doped fiber amplifier and seeded by a cavity dumped Ti:Sapphire oscillator. Picosecond pump pulses for the OPCPA are generated by spectral filtering and directly amplified to 1 mJ pulse energy in several fiber amplifiers, without the need of chirped pulse amplification. Since no stretcher and compressor is required, the pump laser is very compact and easy to operate. The two stage optical parametric amplifier delivers 35 fs pulses with 53 microJ pulse energy and 1.1 GW peak power at 40 kHz repetition rate. Additionally, the scaling potential of this approach is discussed.

Broadly tunable carrier envelope phase stable optical parametric amplifier pumped by a monolithic ytterbium fiber amplifier

In an effort to develop a robust and efficient front end for a chirped-pulse parametric amplification chain, we demonstrate a broadband difference-frequency converter driven by a monolithic femtosecond Yb-doped-fiber amplifier and emitting carrier-envelope-offset-free pulses with the energy of tens of nanojoules tunable in the wavelength range from 1200 nm to beyond 2 mum. Next to providing these seed pulses, the system enables direct optical synchronization of Nd- and Yb-doped pump lasers for subsequent parametric amplification.

Generation of sub-three-cycle, 16 TW light pulses by using noncollinear optical parametric chirped-pulse amplification

We present a two-stage noncollinear optical parametric chirped-pulse amplification system that generates 7.9 fs pulses containing 130 mJ of energy at an 805 nm central wavelength and 10 Hz repetition rate. These 16 TW light pulses are compressed to within 5% of their Fourier limit and are carefully characterized by the use of home-built pulse diagnostics. The contrast ratio before the main pulse has been measured as 10(-4), 10(-8), and 10(-11) at t=-3.3 ps, t=-5 ps, and t=-30 ps, respectively. This source allows for experiments in a regime of relativistic light-matter interactions and attosecond science.

Powerful wavelength-tunable ultrashort solitons in a solid-core photonic-crystal fiber

A solid-core photonic-crystal fiber (PCF) with an effective mode area of 20 microm2 is used to demonstrate the generation of sub-100-kW, 30-70 fs wavelength-tunable solitons within a wavelength range of 1300-1800 nm at a repetition rate of 18 MHz. An energy of 2.9 nJ per pulse is achieved for a 35 fs soliton PCF output centered at 1770 nm. Our numerical analysis supports experimental findings and suggests that frequency-shifted solitons in solid-core PCFs can be scaled up to a submegawatt level of peak powers.

Stabilized soliton self-frequency shift and 0.1- PHz sideband generation in a photonic-crystal fiber with an air-hole-modified core

Fiber dispersion and nonlinearity management strategy based on a modification of a photonic-crystal fiber (PCF) core with an air hole is shown to facilitate optimization of PCF components for a stable soliton frequency shift and subpetahertz sideband generation through four-wave mixing. Spectral recoil of an optical soliton by a red-shifted dispersive wave, generated through a soliton instability induced by high-order fiber dispersion, is shown to stabilize the soliton self-frequency shift in a highly nonlinear PCF with an air-hole-modified core relative to pump power variations. A fiber with a 2.3-microm-diameter core modified with a 0.9-microm-diameter air hole is used to demonstrate a robust soliton self-frequency shift of unamplified 50-fs Ti: sapphire laser pulses to a central wavelength of about 960 nm, which remains insensitive to variations in the pump pulse energy within the range from 60 to at least 100 pJ. In this regime of frequency shifting, intense high- and low-frequency branches of dispersive wave radiation are simultaneously observed in the spectrum of PCF output. An air-hole-modified-core PCF with appropriate dispersion and nonlinearity parameters is shown to provide efficient four-wave mixing, giving rise to Stokes and anti-Stokes sidebands whose frequency shift relative to the pump wavelength falls within the subpetahertz range, thus offering an attractive source for nonlinear Raman microspectroscopy.

Soliton self-frequency shift decelerated by self-steepening

Self-steepening of ultrashort light pulses is shown to reduce the soliton self-frequency shift (SSFS) induced by the Raman effect in an optical fiber. We derive an analytical expression for the SSFS that conserves the number of photons and allows the SSFS to be calculated for arbitrary frequency profiles of fiber dispersion and Raman gain without a numerical solution of the pulse evolution equation. The accuracy of this analytical approach to SSFS calculation is tested by numerical simulations based on the generalized nonlinear Schrödinger equation.

Two-dimensional coherent superposition of blue-shifted signals from an array of highly nonlinear waveguiding wires in a photonic-crystal fiber

Frequency-shifted dispersive optical waves generated as a result of soliton dynamics of 30-fs Ti: sapphire-laser pulses in an array of waveguiding wires, implemented on a platform of a photonic-crystal fiber (PCF), are shown to produce regular stable interference patterns with high visibility, indicating a high coherence of frequency-shifted fields. For a hexagonal array of waveguides built into a silica PCF, the field intensity at the main peak of a six-beam interference pattern was found to be a factor of 22 higher than the intensity of a frequency-shifted signal from an individual waveguide in the array and 3.7 times higher than the field intensity attainable through an incoherent superposition of the same fields.

Parametric amplification and compression to ultrashort pulse duration of resonant linear waves

We report on an optical parametric amplification system which is pumped and seeded by fiber generated laser radiation. Due to its low broadening threshold, high spatial beam quality and high stability, the fiber based broad bandwidth signal generation is a promising alternative to white light generation in bulky glass or sapphire plates. We demonstrate a novel and successful signal engineering implemented in a setup for parametric amplification and subsequent recompression of resonant linear waves resulting from soliton fission in a highly nonlinear photonic crystal fiber. The applied pump source is a high repetition rate ytterbium-doped fiber chirped pulse amplification system. The presented approach results in the generation of ~50 fs pulses at MHz repetition rate. The potential of generating even shorter pulse duration and higher pulse energies will be discussed.

Perturbative analytical treatment of adiabatically moderated soliton self-frequency shift

We provide a perturbative analytical treatment of the soliton self-frequency-shift (SSFS) in optical fibers including the main physical mechanisms limiting the SSFS, such as the high-order dispersion, the wavelength dependence of the effective mode area, and optical loss. We use this approach to estimate the frequency shift of a soliton with adiabatically varying local parameters and compare this estimate with the results of numerical simulations for SSFS in photonic-crystal fibers. This comparison shows that, in many situations of practical interest, the proposed approach can adequately predict important tendencies of SSFS, and allows a fair estimation of characteristic length scales for the mechanisms limiting the SSFS.

Multifrequency third-harmonic generation by red-shifting solitons in a multimode photonic-crystal fiber

While the standard scenario of third-harmonic generation (THG) by a dispersive-wave pump involves the emission of light with a frequency 3omega, thrice the frequency omega of the input pump field, solitons undergoing a continuous shift of their central frequency omega due to the Raman effect in a multimode optical fiber can generate the third harmonic in a different fashion. In the experiments reported here, we provide the first direct experimental evidence of THG by a continuously red-shifting soliton pump by studying the third-harmonic buildup in relation to the spectral evolution of the soliton pump field in a silica photonic-crystal fiber (PCF). We show that solitons excited in a PCF by unamplified femtosecond pulses of a Cr:forsterite laser sweep through the spectral range from 1.25 to 1.63 microm , scanning through a manifold of THG phase-matching resonances with 3omega dispersive waves in PCF modes. As a result, intense third-harmonic peaks build up in the range of wavelengths from 370 to 550 nm at the output of the fiber, making PCF a convenient fiber-format multifrequency source of short-wavelength radiation. Time-resolved fluorescence measurements with photoexcitation provided by the third-harmonic PCF output are presented, demonstrating the high potential of PCF sources for an ultrafast photoexcitation of fluorescent molecular systems in physics, chemistry, and biology.

Wavelength-tunable ultrashort-pulse output of a photonic-crystal fiber designed to resolve ultrafast molecular dynamics

Wavelength-tunable 100 fs pulses generated through the soliton self-frequency shift in a photonic-crystal fiber are employed to visualize femtosecond coherence and population relaxation dynamics in molecular aggregates by means of time-resolved sum-frequency generation. This technique reveals an ultrafast dephasing of coherent molecular excitations with a phase relaxation time of about 120 fs and resolves an ultrafast switching of the nonlinear-optical response of molecular aggregates.

Spectral transformation of femtosecond Cr:forsterite laser pulses in a flint-glass photonic-crystal fiber

Nonlinear-optical performance of photonic-crystal fibers (PCFs) made of highly nonlinear TF10 glass is studied and compared with the general tendencies of nonlinear-optical interactions in fused-silica PCFs. The loss of TF10 glass PCFs prevents the generation of supercontinuum emission with a broad and flat spectrum, which typically requires propagation lengths comparable with or exceeding the attenuation length of the fiber. However, dispersive-wave emission of solitons, induced by high-order dispersion, phase-matched four-wave-mixing processes, and self-phase-modulation-induced spectral broadening are substantially enhanced in TF10 glass PCFs due to the high material nonlinearity, providing a high efficiency of frequency conversion of Cr:forsterite laser pulses.

Widely tunable soliton frequency shifting of few-cycle laser pulses

Photonic-crystal fibers are employed to demonstrate widely tunable frequency down-conversion of unamplified 6-fs Ti:sapphire laser pulses through the soliton self-frequency shift induced by the Raman effect. Wavelength shifts as large as 500 nm are achieved for input few-cycle pulses with broadband spectra centered at approximately 820 nm. The central wavelength of the redshifted output of a photonic-crystal fiber is smoothly tuned from the low-frequency edge in the spectrum of the 6-fs Ti:sapphire laser pulse up to 1.35 microm by varying the input energy in the fundamental mode of the fiber.

Diffraction-arrested soliton self-frequency shift of few-cycle laser pulses in a photonic-crystal fiber

The balance between diffraction and index-step guiding in photonic-crystal fibers is controlled by modifying the fiber structure, leading to different wavelength dependences of the effective mode area and providing a mechanism to control nonlinear-optical phenomena. In optical fibers with a steep profile, the guided mode of the light field tends to become much less compact with an increase in radiation wavelength, slowing down the Raman-induced soliton self-frequency shift of an ultrashort laser pulse. A reduction of the soliton self-frequency shift is demonstrated for input laser pulses.

Nonlinear-optical spectral transformation of few-cycle laser pulses in photonic-crystal fibers

Photonic-crystal fibers with special dispersion profiles are shown to provide a high efficiency of spectral transformation of chirped sub-6-fs Ti:sapphire laser pulses. With the wavelength of zero group-velocity dispersion of the fiber lying within the broad spectrum of the input few-cycle pulse, the output spectra feature well-resolved spectral peaks, indicative of soliton self-frequency shift, four-wave mixing, and Cherenkov emission of dispersive waves. We demonstrate that up to 3% of radiation energy at the output of the fiber can be confined within a spectrally isolated soliton peak centered at , which is ideally suited as a seed for Nd:YAG- and ytterbium-based laser devices.