Pulse compression to 3-cycle duration beyond 300 W average power

A confocal, reflection-double-pass, Ti:sapphire continuous-wave amplifier with a small-signal gain of 4.2 has been invented. Femtosecond pulses with an 82-MHz repetition rate from a mode-locked Ti:sapphire laser are amplified to 5.77-W average power through an amplifier pumped by three cw green lasers, and the extraction efficiency reaches 10.6 %.

In this study we demonstrate the suitability of Hollow-Core Photonic Crystal Fibers (HC-PCF) for multiwatt average power pulse compression. We spectrally broadened picosecond pulses from a SESAM mode-locked thin disk laser in a xenon gas filled Kagome-type HC-PCF and compressed these pulses to below 250 fs with a hypocycloid-core fiber and 470 fs with a single cell core defect fiber. The compressed average output power of 7.2 W and 10.2 W at a pulse repetition rate of approximately 10 MHz corresponds to pulse energies of 0.7 µJ and 1 µJ and to peak powers of 1.6 MW and 1.7 MW, respectively. Further optimization of the fiber parameters should enable pulse compression to below 50 fs duration at substantially higher pulse energies.

We demonstrate wavelength tunability of femtosecond pulses over a range of more than 50 nm from a diode-pumped Cr:LiSAF laser. The mode-locking mechanism can be explained by soliton mode locking that is started and stabilized by a broadband semiconductor saturable-absorber mirror designed for low loss over the full reflection bandwidth of the underlying Bragg mirrors, which ultimately limits tunability. We obtain 45-fs pulses at 105-mW average output power and a maximum mode-locked average output power of 125 mW with 60-fs pulses.

In recent years, compression schemes based on distributed spectral broadening in gas-filled multi-pass cells (MPC) have been demonstrated to support millijoule pulse energies [1] , [2] . We experimentally demonstrate the scaling of such a MPC to kilowatt average power. A fiber laser source coherently combining 16 amplifier channels provides ~1-mJ, 200-fs pulses at a repetition rate of 1 MHz resulting in an average power of ~1 kW [3] . The laser output is compressed by distributed spectral broadening in 26 foci of an Argon-filled MPC and subsequent chirped-mirror compression to 31-fs pulses (see Fig. 1 ) with an average power of 1 kW demonstrating a mirror-reflectivity-limited compression efficiency of >95% [4] . To the best of our knowledge, the MPC output represents the highest average power of sub-100-fs pulses ever demonstrated. Sound characterization of the output in terms of spatio-spectral couplings and beam quality factor reveals a close-to lossless compression [4] .

In recent few years, femtosecond fiber lasers have been developed with ever increasing performances in terms of pulse energy. The energy produced in a mode-locked fibre oscillator has been increased from some nanojoules to several hundreds of nanojoules. This breakthrough results from the emergence of low-nonlinearity Yb-doped large mode area (LMA) fibers and progress in development of high contrast semiconductor saturable absorber mirrors (SESAM). As the first reported laser based on this concept, an Yb-doped fiber laser generating 0.9 W of average output power in 500-fs soliton pulses was demonstrated [1]. More recently, a significant energy scaling (up to more than 0.25 µJ) in femtosecond pulses has been demonstrated thanks to the use of these new fiber designs in purely-normal dispersion laser configurations [2,3]. Further energy scaling should be possible by incorporation of one or more segments possessing large positive dispersion to achieve the so-called chirped-pulse oscillator configuration [4]. In this contribution, we report on generation of high-energy femtosecond pulses from a mode-locked chirped-pulse oscillator featuring large-mode-area fibers. The laser is based on a 1.3 m long LMA microstructure fiber featuring a 40 µm Yb-doped core and a fast saturable absorber mirror for passive mode-locking. The total cavity dispersion is controlled by insertion of a passive LMA microstructure fiber with a core diameter of 25 µm. Preliminary results are obtained using a 3 m long LMA passive fiber leading to a total cavity dispersion of 0.09 ps2. In this configuration, we obtain self-starting modelocking for an average output power of 500 mW at a repetition rate of 33 MHz. The single-pulse operation is maintained up to an average output power as high as 3 W, which results in an energy per pulse of 91 nJ.

We report on an Er-doped fiber laser which can generate few-cycle pulses with excellent long-term stability. The all-polarization-maintaining fiber oscillator can produce 50-fs pulses with 13.6-mW average output power at 85.3-MHz repetition rate.

We present a high peak and average power laser system with ultrashort pulses at high repetition rates. Pulse shortening and peak power enhancement of a state-of-the-art fiber laser system is achieved by utilizing nonlinearity, namely selfphase modulation and subsequent compression in a chirped mirror compressor. The nonlinear interaction is achieved by propagation in a noble gas filled hollow core fiber with an inner diameter of 200 μm and a length of 0.5 m. A total second dispersion of -7000 fs² is applied by a chirped mirror compressor resulting in ultrashort pulses of 71 fs duration. This is achieved by coupling 400 MW, 800 fs pulses from the CPA system to the Xenon filled hollow core fiber. The average power at the output of the compressor is measured to be 10 W at 50 kHz repetition rate resulting in 200 μJ pulse energy. Hence, the compressed pulses have a peak power of more than 2 GW. Consequently, the pulses of the CPA system are shortened by a factor of ten and the peak power is enhanced by a factor of 5. In addition this approach offers further peak and average power scalability.

We demonstrate high average power, high peak power amplification of 10 GHz, picosecond and femtosecond pulses in a very-large-mode-area (VLMA), Er-doped fiber with an effective area of ∼1100 μm2. A high-power, single-mode Raman fiber laser with up to 183 W of power at 1480 nm served as the pump source. When amplifying 3 ps pulses at 1560 nm, a maximum average power of 120 W was demonstrated. Using an additional highly nonlinear fiber for pulse compression before the VLMA amplifier, 130 fs pulses with an average power of 115 W, peak power of 88 kW, and M2 of 1.18 were achieved. To the best of our knowledge, this is the first time ultrashort pulses in the 1550 nm wavelength region have been amplified to average powers in excess of 100 W in an Er-fiber amplifier.

In this contribution we demonstrate the nonlinear pulse compression of an ultrafast thulium-doped fiber laser down to 14 fs FWHM duration (sub-3 optical cycles) at a record average power of 43 W and 34.5 μJ pulse energy. To the best of our knowledge, we present the highest average power few-cycle laser source at 2 μm wavelength. This performance level in combination with GW-class peak power makes our laser source extremely interesting for driving high-harmonic generation or for generating mid-infrared frequency combs via intra-pulse frequency down-conversion at an unprecedented average power. The experiments were enabled by an ultrafast thulium-doped fiber laser delivering 110 fs pulses at high repetition rates, and an argon gas-filled antiresonant hollow-core fiber (ARHCF) with excellent transmission and weak anomalous dispersion, leading to the self-compression of the pulses. We have shown that ARHCFs are well-suited for nonlinear pulse compression around 2 μm wavelength and that this concept features excellent power handling capabilities. Based on this result, we discuss the next steps for energy and average power scaling including upscaling the fiber dimensions in order to fully exploit the capabilities of our laser system, which can deliver several GW of peak power. This way, a 100 W-class laser source with mJ-level few-cycle pulses at 2 μm wavelength is feasible in the near future.

Powerful techniques for spectral broadening and ultrabroadband dispersion control, which allow the compression of high-energy femtosecond pulses to a duration of a few optical cycles, are presented. Spectral broadening by propagation along hollow-core fused silica fiber filled with atomic and molecular gases is studied under two excitation regimes with high-energy input pulses of 140 fs and 20 fs duration respectively. Conditions for optimum pulse compression are outlined considering the role of self-phase modulation and gas dispersion in the two regimes. With 20 fs input pulses and under optimum compression conditions we demonstrate a pulse shortening down to 4.5 fs with output energy up to 70 μJ using a high-throughput prism-chirped-mirror delay line. These pulses are the shortest generated to date at multigigawatt peak power. PACS: 42.65.Re; 42.65.Vh Ultrashort-pulse lasers are the most important experimental tools for investigating fast-evolving atomic and molecular dynamics in physics, chemistry, and biology. In the last few years, great technological advances have been made in the field of ultrafast pulse generation. New mode-locking techniques such as additive-pulse mode-locking and Kerr-lens mode-locking have been successfully used for femtosecond pulse generation from a wide range of solid-state laser oscillators [1]. Using chirped mirrors [2] for intracavity dispersion control, pulses down to 7.5 fs have been directly generated by a Kerr-lens mode-locked Ti:sapphire oscillator [3] and, more recently, 6.5-fs pulses have been obtained using broadband semiconductor saturable absorbers for self-starting [4]. Ti:sapphire amplifiers seeded by femtosecond laser oscillators can now generate pulses of 20–30 fs with gigawatt [5, 6] or terawatt [7–9] peak power at repetition rates in the kHz and 10 Hz regimes, respectively. Ultrashort pulses can also be generated by extracavity compression techniques, in which the pulses are spectrally broadened upon propagation in a suitable nonlinear waveguide and subsequently compressed in a carefully designed optical dispersive delay line. Spectral broadening of laser pulses by self-phase modulation (SPM) in a single-mode optical fiber is a well-established technique: pulses down to 6 fs were obtained in 1987 from 50-fs pulses from a mode-locked dye laser [10]. More recently 13-fs pulses from a cavity-dumped Ti:sapphire laser were compressed to 5 fs with the same technique [11]. However, the use of single-mode fibers limits the pulse energy to a few nanojoules. A powerful pulse compression technique based on spectral broadening in an hollow fiber filled with noble gases has demonstrated the capability of handling highenergy pulses (sub-mJ range) [12]. This technique presents the advantages of a guiding element with a large diameter mode and of a fast nonlinear medium with high threshold for multiphoton ionization. New concepts in the construction of dispersive delay lines have been applied in the development of specially designed chirped mirrors for fine control of cubic and quartic phase dispersion terms over a large spectral bandwidth [3]. The implementation of the hollow-fiber technique using 20-fs seed pulses from a Ti:sapphire system [5] and a high-throughput broadband dispersive delay line consisting of prisms and chirped mirrors has recently permitted the generation of multigigawatt sub-5 fs pulses [13]. In this paper we present a comprehensive analysis of compression experiments with high-energy femtosecond pulses performed using gas-filled hollow fibers. Spectral broadenings obtained in different gases are compared for 140-fs and 20-fs input pulses generated by Ti:sapphire laser systems, and the optimum conditions for pulse compression are outlined considering the role of SPM and gas dispersion. A new ultrabroadband prism-chirped-mirror dispersive delay line, characterized by a high throughput and dispersion control up to the fourth order, is described in detail. The paper is organized as follows. In Sect. 1 we provide a description of hollow fiber modes and discuss the major advantages of this device compared to optical fibers. Sect. 2 reports on typical spectral broadenings achieved under different excitation conditions. In Sect. 3 we report on the characteristics of the prism-chirped-mirror compressor and discuss the experimental results obtained with 20-fs input pulses. Under optimum compression conditions we show a pulse shortening down to 4.5 fs with output energy up to 70 μJ. These pulses are the

We firstly report a high pulse repetition rate (101.4 MHz) nonlinear post-compression based on the normal dispersion fiber (NDF) operating in 2-µm wavelength region. With only one-stage NDF-based nonlinear pulse compressor, the 2-µm ultrafast laser pulses are compressed from ∼460 fs down to 70 fs, corresponding to ∼10.4 optical oscillation cycle. With two-stage nonlinear pulse compressor, the input ultrafast laser pulses are further compressed to 28.3 fs (∼4.3 optical oscillation cycle). In each case, the average power of the compressed 2-µm laser pulses exceeds 1 W, which is believed to be the highest average power never achieved at ∼100-MHz pulse repetition rate. The efficiencies of the one-stage and two-stage nonlinear pulse compressors are 64% and 47% respectively.

The naval research laboratory has recently developed a high power 94 GHz radar with scanning capability, WARLOC. It relies on three advances in millimeter wave capability, a gyroklystron, designed at NRL and manufactured at CPI [2,3], a quasi-optical duplexer [4] developed by Lincoln laboratory, and an overmoded waveguide transmission system developed by General Atomics. The WARLOC transmitter is designed to generate up to 100 kW of peak power and 10 kW of average power at 94 GHz; operation to date has been approximately 70 kW peak power and 2 kW average power. This is about three orders of magnitude more average power than W band radar cloud system. Here we report initial results on cloud studies. New capabilities of WARLOC include imaging with greatly improved sensitivity and detail, the ability to detect much lower cloud returns, the capability of using chirped pulses with pulse compression for high resolution, the rapid generation of high resolution three dimensional images, and the possibility of producing extremely fine scale images with stretch processing. WARLOC is now set up on the western shore Chesapeake Bay. This talk presents some of the first cloud images obtained.

We report the nonlinear pulse compression of a high-power, thulium-doped fiber laser system using a gas-filled hollow-core fiber. The sub-two cycle source delivers 1.3 mJ pulse energy with 80 GW peak power at a central wavelength of 1.87 μm and an average power of 132 W. This is, so far, to the best of our knowledge, the highest average power of a few-cycle laser source reported in the short-wave infrared region. Given its unique combination of high pulse energy and high average power, this laser source is an excellent driver for nonlinear frequency conversion, toward terahertz, mid-infrared, and soft X-ray spectral regions.

A Yb-fiber frequency comb with 120 fs pulse duration, 154 MHz repetition rate, and 80 W average power is used for cavity-enhanced high harmonic generations. Plateau harmonics beyond the microwatt level have been demonstrated.

Dual-comb laser sources offer significant performance advantages compared to traditional laser sources in various optical sensing applications, such as high-resolution spectroscopy, rapid pump-probe measurements and ranging [1] . Dual-comb generation from a single laser cavity is particularly relevant for advancing practical dualcomb applications due to reduced complexity and cost. By using a birefringent polarization multiplexing of the cavity we have demonstrated dual-comb modelocking in diode-pumped semiconductor disk and solid-state lasers [2] - [4] . Here we present a significant performance scaling of this novel architecture to more than 2.1 W of average power per comb with significantly shorter 100-fs output pulse duration.