We present a tunable, high-energy optical parametric chirped pulse amplification system with a front-end based on a femtosecond Cr:ZnS laser. By taking advantage of the broad emission spectrum of the ...femtosecond Cr:ZnS master oscillator, we are able to directly seed the holmium-based pump around 2 µm. At the same time, the signal pulses for the parametric process are generated via Raman self-frequency shifting of the red end of the spectrum centered at 2.4 µm. The solitons, generated in a fluoride fiber, are tunable over the wavelength range between 2.8 and 3.2 µm. The optical parametric amplifier operates at a 1 kHz repetition rate, and consists of two stages equipped with ZGP as nonlinear crystal. The generated idler pulses are tunable between 5.4 and 6.8 µm with a pulse energy of up to 400 µJ. Dispersion management using bulk material stretching and compression in combination with precise phase shaping prior to amplification enables idler pulses of a sub-100 fs duration, translating into a peak power as high as 4 GW.
A Tm-doped mixed sesquioxide ceramic laser is mode-locked near 2 µm using InGaAsSb quantum-well semiconductor saturable absorber and chirped mirrors for dispersion compensation. Maximum average ...output power of 175 mW is achieved for a pulse duration of 230 fs at a repetition rate of 78.9 MHz with a 3% output coupler. Applying a 0.2% output coupler pulses as short as 63 fs are generated at 2.057 µm.
Cubic sesquioxides, RE 2 O 3 , where RE = Y, Lu or Sc, are attractive host crystals for thulium (Tm 3+ ) doping. A comparison of the spectroscopic properties of Tm 3+ :RE 2 O 3 crystals in terms of ...transition cross sections and cross-relaxation (CR) efficiency required for efficient upconversion pumping is presented. Thermo-optic properties of Tm 3+ :RE 2 O 3 crystals (thermal lensing, fractional heat loading, and thermo-optic coefficients) are described. The positive thermal lens, broadband emission, and efficient CR of the Tm:RE 2 O 3 crystals enable the development of compact, highly efficient and power-scalable lasers operating above 2 μm, based on thermal guiding. Nowadays, Tm:Lu 2 O 3 microchip lasers are capable of generating nearly 5 W of output power at ~2.06 μm with a slope efficiency η of 67% and in a rod geometry-up to 47.5 W with η of 59%. For multiwatt output at even longer wavelengths around 2.15 μm, Tm:Sc 2 O 3 is an interesting candidate.
The generation of sub-five optical cycle pulses centered at 11.2 µm wavelength with 50 µJ energy at a 1 kHz repetition rate is reported. A GaSe optical parametric chirped pulse amplifier (OPCPA) is ...driven by the residual 2.0 µm pump and 5 µm idler of a high-energy midwave-IR OPCPA. The latter serves as driver for hard X-ray generation and this makes the achieved fs longwave-IR pulses available for X-ray pump-probe experiments.
We demonstrate the suitability of monoclinic double tungstates (MDTs), KRE(WO 4 ) 2 , where RE = Gd, Y or Lu, doped with Nd 3+ , Yb 3+ , Tm 3+ , or Ho 3+ ions and co-doped with Yb 3+ -Tm 3+ , or Tm ...3+ -Ho 3+ ion couples, for highly efficient micro-lasers at ~1 μm and at ~2 μm. This is facilitated by the use of high rare-earth doping levels (up to 15 at.% for Tm, 10 at.% for Nd, and 25 at.% for Yb) and a special crystal cut along the Ng-axis providing the thermal guiding. Record slope efficiencies for bulk MDT lasers are achieved for each studied ion. A 15 at.% Tm:KLu(WO 4 ) 2 laser generated 785 mW at 1957...1965 nm with a slope efficiency η = 77%. The quantum efficiency for Tm 3+ ions amounted to η q = 1.98±0.02. With a 0.9 mm-thick 25 at.% Yb:KLuW micro-laser, η = 91% is achieved, approaching the theoretical limit set by the Stokes shift.
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