We report on a 300-W industrial femtosecond laser with ultrashort compressed pulses. Pulse compression is performed within a gas-filled multi-pass cell and results in about 50fs pulses at an energy of 600µJ. Long terms tests of more than 10 days revealed excellent long term and short-term stability of the system. Relevant laser and system parameters are continuously monitored and logged thus enabling to correlate these parameters with results obtained when using this laser for scientific experiments or machining applications. The perspectives to even shorter pulses and higher power and pulse energies will be discussed.
We report on an ultra-broadband tunable mid-IR source delivering 110 nJ, 64 fs-long pulses at 250 kHz repetition rate. The experiment starts with a Yb-doped fiber amplifier system delivering 200 μJ, 300 fs-long pulses, followed by a 70% high-efficiency dual-stage nonlinear compression based on a multipass cell and a 1 m-long capillary filled with argon. The 9.5 fs-long resulting pulses drive intrapulse difference-frequency generation (iDFG) in a 1 mm-thick LiGaS2 crystal and a specially designed waveplate is used prior to this crystal to further enhance the iDFG yield. This source paves the way for new experiments in 2D ultrafast spectroscopy.
We report on an agile nonlinear device able to generate 300W, mJ-level, transform-limited pulses from few picoseconds down to few tens of femtoseconds. The system is based on an industrial-grade 330W laser, delivering 400fs pulses followed by an efficient, >90% throughput, gas-filled multipass cell where self-phase modulation occurs. Adjustment of the chamber gas pressure and incoming pulse chirped either favors spectral compression or nonlinear compression, leading to the generation 300W, 1mJ, high beam quality and nearly transform-limited pulses of 2ps down to 30fs within a single system. This source is a versatile tool for both industrial and scientific applications.
Nowadays, the request for femtosecond lasers operating between 1.7 μm and 2 μm is continuously growing for many applications. Mode-locked Holmium- or Thulium-doped fiber lasers based on Saturable Absorber Mirror (SAM) are typically the first approach to generate pulses in this spectral range but this technique suffers from a lack of tunability. Indeed, the operating wavelength is fixed by the SAM and the gain fiber. Another way to reach the 2 μm-spectral range consists to exploit the nonlinear phenomena appearing in optical fibers and in particular the Soliton-Self Frequency Shift (SSFS) effect from an Erbium-fiber laser. Several systems based on this phenomenon allowed the generation of ultrashort pulses at different wavelengths and in different type of fibers (step-index, PCF, …). In this paper, we report on the design of a compact and robust all-Polarization-Maintaining (PM) fiber system entirely based on commercial PM components. This system allows to generate a single femtosecond pulse continuously tunable from 1700 nm to 2050 nm. We also demonstrate that the sub-150 fs pulses are transform-limited over all the spectral range and thanks to an optimized rate conversion close to 50 %, the pulse energy and the peak power can reach the nJclass and the kW-class respectively, which represents a gain a of factor 2 compared to the previous works.
We report on the CEP stabilization of a nonlinearly compressed Yb-doped fiber amplifier system delivering 75 μJ, 60 fs-long pulses at 100 kHz repetition rate. The CEP is passively stabilized via DFG in a home-made front-end and preserved in the amplification chain using a fast feedback loop. A CEP noise of only 320 mrad is measured single shot, every shot at 100 kHz. This source paves the way for a new generation of high repletion rate HHG driver.
Nowadays, the request for femtosecond lasers operating between 1.7 μm and 2 μm is continuously growing for many applications. Mode-locked Holmium- or Thulium-doped fiber lasers based on Saturable Absorber Mirror (SAM) are typically the first approach to generate pulses in this spectral range but this technique suffers from a lack of tunability. Indeed, the operating wavelength is fixed by the SAM and the gain fiber. Another way to reach the 2 μm-spectral range consists to exploit the nonlinear phenomena appearing in optical fibers and in particular the Soliton-Self Frequency Shift (SSFS) effect from an Erbium-fiber laser. Several systems based on this phenomenon allowed the generation of ultrashort pulses at different wavelengths and in different type of fibers (step-index, PCF, …). In this paper, we report on the design of a compact and robust all-Polarization-Maintaining (PM) fiber system entirely based on commercial PM components. This system allows to generate a single femtosecond pulse continuously tunable from 1700 nm to 2050 nm. We also demonstrate that the sub-150 fs pulses are transform-limited over all the spectral range and thanks to an optimized rate conversion close to 50 %, the pulse energy and the peak power can reach the nJclass and the kW-class respectively, which represents a gain of a factor 2 compared to the previous works.
We describe an optical parametric chirped pulse amplifier (OPCPA) architecture built around a state of the art Yb-doped fiber femtosecond pump source delivering 300 fs 400 μ pulses at a repetition rate 125 kHz (50 W average power) and a central wavelength of 1030 nm. The short pump pulse duration compared to bulk Yb:YAG or Nd:YVO4 based systems results in a number of important advantages. First, it allows efficient seeding at 1550 nm using supercontinuum generation directly from the pump pulses in a bulk YAG crystal, resulting in extremely robust passive pump-signal synchronization. The short pump pulse duration also allows the use of millimeter to centimeter lengths of bulk materials to provide stretching and compression for the signal and idler, which minimizes the accumulation of higher-order spectral phase. Finally, the shorter pump pulse duration increases the damage peak intensity, permitting the use of shorter nonlinear crystals to perform the amplification, which increases the spectral bandwidth of the parametric process. Additional experiments are performed to sort out the phenomena that limit power scaling in MgO:PPLN crystals. The OPCPA stages are all operated in collinear geometry, allowing the use of both signal and idler without the introduction of angular chirp on the latter. These points result in the dual generation of 70 fs 23 μJ signal pulses at 1550 nm and 60 fs 10 μJ idler pulses at 3070 nm from a simple setup, with the added benefit of inherent CEP stability of the idler pulses.
A hybrid ytterbium-doped fiber – bulk laser source generating up to 116MW peak power for 3ps pulse duration at 50kHz repetition rate and 1030nm wavelength is presented. Tunability of the pulse duration is made by spectral compression occurring into the seeder. Divided Pulse Amplification scheme is investigated to study energy capabilities of the setup.
We report the generation of 10 μJ, ultrashort 97 fs pulses at 1 MHz by implementing a two-arm spectral coherent combining scheme in a fiber chirped-pulse amplifier (FCPA), allowing both gain-narrowing mitigation and large stretching ratio for energy extraction. Such architecture is able to support the amplification of large-bandwidth (>15 nm) together with high gain factor (>30 dB), allowing the generation of ultrashort sub-100 fs pulses at the output of a FCPA for the first time.
The duration of energetic ultrashort pulses is usually limited by the available gain bandwidth of ultrashort amplifiers used to amplify nJ or pJ level seed to hundreds of μμJ or even several mJ. In the case of Ytterbium-doped fiber amplifiers, the available bandwidth is of the order of 40 nm, typically limiting the pulse duration of high-energy fiber chirped-pulse amplifiers to durations above 300 fs. In the case of solid-state amplifier based on Yb:YAG crystals, the host matrix order restricts the amplification bandwidth even more leading to pulses in the low picosecond range. Both architecture would greatly benefit from pulse durations well-below what is allowed by their respective gain bandwidth e.g. sub-100 fs for fiber amplifier and sub-300 fs for solid-state Yb:YAG amplifier. In this contribution, we report on the post-compression of two high energy industrial ultrashort fiber and thin-disk amplifiers using an innovative and efficient hollow core fiber structure, namely the hypocycloid-core Kagome fiber. This fiber exhibits remarkably low propagation losses due to the unique inhibited guidance mechanism that minimize that amount of light propagating in the silica cladding surrounding the hollow core. Spectral broadening is realized in a short piece of Kagome fiber filled with air at 1 atmosphere pressure. For both amplifiers, we were able to demonstrate more than 200 μJ of energy per pulse with duration <100 fs in the case of the fiber amplifier and <300 fs in the case of the thin disk amplifier. Limitations and further energy scaling will also be discussed.
Femtosecond fiber chirped pulse amplifiers have numerous advantages, but are limited in energy because of the small interaction area with the fiber core. In this contribution, we create two orthogonally-polarized stretched pulse replicas in the time domain, following the divided-pulse amplification (DPA) principle. This beam is subsequently separated into two counter-propagating beams in a Sagnac interferometer to finally generate four pulse replicas. These pulses are amplified in two state-of-the-art large mode area rod-type fiber amplifiers in series, before final coherent combination and compression.
Because the stretched-pulse duration is of the order of hundreds of picoseconds, the DPA delay is induced using a freespace interferometer with reasonable arm lengths of few tens of centimeters. The use of a common interferometer to divide and recombine temporal pulse replicas, together with the Sagnac geometry, results in an identical optical path for all four replicas. Therefore, the whole spatio-temporal combining architecture is passive, avoiding the need for active electronic stabilization systems. Because we only use two temporal replicas, the system is immune to differential saturation levels or B-integrals between successive pulses: this is compensated by controlling the amplitude of both pulses at the input of the amplifying setup.
This setup allows the generation of 1 mJ, 300 fs compressed pulses at 50 kHz repetition rate, corresponding to 50 W output average power, with a combining efficiency above 90% at all power levels.
We implement, in the same femtosecond fiber amplifier setup, both chirped pulse amplification and divided pulse amplification. With the generation of temporally delayed replicas this scheme allows an equivalent stretched pulse duration of more than 1ns in a compact tabletop system. The generation of 45 W of compressed average power at 100 kHz, together with 320 fs and 450 μJ pulses, is demonstrated using a rod-type ytterbium-doped fiber.
We demonstrate spectral coherent beam combining of two femtosecond fiber chirped-pulse amplifiers seeded by a common oscillator. Using active phase stabilization based on an electro-optic phase modulator, an average power of 10 W before compression and a high gain factor of 30 dB is obtained. At this gain value, 130 fs pulses with a spectral width of 19 nm can be generated, highlighting the strong potential of pulse synthesis for the reduction of the minimum duration of ultrashort pulses in fiber chirped-pulse amplifiers.
Passive spatial and temporal coherent combining schemes are implemented to scale the output energy of a nonlinear temporal compression setup. By generating 32 replicas of the incident femtosecond pulses, the output of a high energy fiber chirped-pulse amplifier can be compressed using self-phase modulation in a large mode area rod-type fiber at peak power levels well beyond the self-focusing threshold of 4 MW. We demonstrate the generation of 71 fs 7.5 μJ pulses at 100 kHz repetition rate, corresponding to a peak power of 86 MW.
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