V. E. Yashin

High average-power ultrafast CPA Yb:KYW laser system with dual-slab amplifier

A diode-pumped, ultrafast Yb:KYW laser system utilizing chirped-pulse amplification in a dual-slab regenerative amplifier with spectral shaping of seeding pulse from a master oscillator has been developed. A train of compressed pulses with pulse length of 181 fs, repetition rate up to 200 kHz, and average power exceeding 8 W after compression and pulse picker was achieved.

A high brightness Q-switched oscillator and regenerative amplifier based on a dual-crystal Yb:KGW laser

We present a dual-crystal Yb:KGW laser that is able to operate as a Q-switched oscillator with output power up to 24 W and pulse length of 20 ns, or as a regenerative amplifier with output power up to 21 W and pulse duration below 200 fs after compression of chirped pulses. Both lasers have excellent beam quality with beam parameter M 2 < 1:2. We discuss some aspects of the design and performance optimization of dual-crystal Yb:KGW laser systems. (Some figures may appear in colour only in the online journal)

Directly diode-pumped femtosecond laser based on an Yb:KYW crystal

Ultrashort pulse laser systems are widely used in many areas such as microprocessing of various materials, the generation of terahertz radiation, nonlinear optics, medical tomography, chemistry, and biology due to the high peak power and large spectral width. For a practical usage of the femtosecond lasers, they must be fairly compact and stable. These conditions are most fully met when laser media are used that allow direct pumping with the radiation from semiconductor injection lasers, which are more compact, reliable, and inexpensive than pumping with solid-state lasers. Since Ytterbium-doped crystals have a broad luminescence band for generating femtosecond pulses less than 500 fs wide, they are attractive as materials for lasers with direct diode pumping. Moreover, the position of the central luminescence wavelength of Yb:KGW and Yb:KYW crystals makes them promising priming sources of femtosecond pulses for amplifiers that operate at wavelengths close to 1 μm (Yb:KGW, Yb-glass, Nd-glass, Yb:YAG, etc.) We developed a femtosecond generator based on the Yb:KYW crystal with direct pumping by the radiation of a laser diode with fiber output of the pump radiation. The use of such pumping, as well as of chirped mirrors to compensate intracavity dispersion, made it possible to generate a continuous sequence of optical pulses 90 fs wide at a frequency of 87.8 MHz with a mean radiation power of more than 1 W. The product of the pulse width by the spectral width is close to the theoretical limit, and this indicates that there is no frequency modulation.

Efficient generation of the second and third harmonics of high-power femtosecond Yb:KGW-laser radiation in nonlinear-optical BBO crystals

The frequency conversion of radiation into the second and third harmonics of a high-power femtosecond laser based on Yb:KGd(WO4)2 (Yb:KGW) crystals in BBO (β-BaB2O4) crystals has been experimentally and quantitatively investigated. Under the optimum compression conditions of femtosecond pulses of width 300 fs, the conversion efficiency into the second harmonic reached 50%, and that into the third harmonic reached 20%. The introduction of additional phase modulation reduced the generation efficiency of the second harmonic to an extent that is different for positive and negative signs of the phase modulation. The results of numerical calculations quantitatively agree with the experimental results.

High-power directly diode-pumped femtosecond Yb:KGW lasers with optimized parameters

We report a diode-pumped Yb:KGW laser that is capable of operating as a Q-switched oscillator or as a regenerative amplifier with average power of more than 20 W. The laser is based on a dual-crystal configuration where the pump thermal load is distributed over relatively long two crystals. It permits a sufficiently large number of passes with low passive losses and maximizes the energy extraction efficiency. The amplification bandwidth was extended by spectral combining of two Yb:KGW crystals with spectrally shifted gain maxima, that allows to mitigate spectral gain narrowing and provides pulse length down to 200 fs after compression in a stretcher-compressor module. The output power saturated with increasing pump power and output beam quality was defined by aberration of thermal lenses. Optimization of laser cavity allows us to compensate thermal lens partially and provide output beams with quality M2<1.2. Efficient frequency doubling and tripling of high-power femtosecond Yb:KGW laser is demonstrated in a nonlinear BBO crystal. Second or third harmonic generation with respective conversion efficiency of 55% or 24% was achieved in a single-pass configuration.

Femtosecond oscillator based on an Yb:KYW crystal with direct laser-diode pumping

This paper describes a femtosecond laser based on Yb:KYW with direct pumping by semiconductor injection lasers. The Yb:KYW laser crystal was pumped longitudinally by the radiation of two InGaAs semiconductor injection lasers that operate at a wavelength of 981nm. The spatial structure of the radiation of the semiconductor lasers was reshaped by the optical system in order to maximize their power concentration in the volume of the laser medium. Femtosecond pulses were generated in the self-synchronization regime of longitudinal modes by using a semiconductor saturable absorber. The mean power of the oscillator reached 150mW at λ≈1030nm when the pulse width was about 200fs. The product of the pulse width by the width of the emission spectrum was only a factor of 1.17 greater than the theoretical limit for the pulse shape described by the sech2 function. The master oscillator thus developed can be used as a self-contained source of femtosecond light pulses and as an initiating source for femtosecond laser amplifier systems.