Femtosecond Laser Operation for Broadband Coherent Light on Active Crystal Under High-Power Diode Pumping
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Due to very simple spectroscopic properties of Yb, the weak quantum defect, the lack of undesired effects like up conversion or concentration quenching, and above all the possibility to use high power diodes to pump these materials, based on diode-pumped bulk materials laser systems are promising in this respect. Also for maximum scientific and industrial applications it is required the development of different femtosecond lasers. Many crystals were proposed in the past decade, for a new generation of femtosecond diode-pumped solid-state lasers. Femtosecond lasers base on orthosilicate crystals like Yb: YSO (1) (Yb3+:Y2SiO5) and Yb: LuSO (Yb3+:LuSiO5) or the crystals Yb: KYW (2) Yb3+: KY (WO4) and Yb: KGW (3,4) (Yb: KGd(WO4)2) have demonstrated high average powers The achievable pulse widths are ≥100fs. Sub- 100 fs pulses were however, on the other hand with Yb: BOYS (5) (Yb3+:Sr3Y(BO3)3) or Yb: SYS (6) (Yb3+: SrY4(SiO4)3O) obtained. Typically higher than low, these crystals are not able to sustain high-power pumping because of a poor thermal conductivity less than 2W/m/K. Even these crystals cannot deliver high average output powers in standard oscillator configurations. However, it shows that a combination of high average power and ultrashort pulses is still a challenger for diode-pumped lasers based on Yb-doped crystal.
To produce mutually coherent equidistant frequency sidebands scanning several octaves of optical bandwidths, broadband collinear Raman generation in molecular gases has been used recently (7). These sidebands can be used to synthesize optical pulses as short as a fraction of a femtosecond (8). This type of technique relied on adiabatic preparation of near-maximal molecular coherence. But at present isolated at...
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...onds to an energy per pulse of 5nJ or 64 kW peak power.
It is demonstrated that the generation of 68 fs pulses centered at 1050 nm with a 2 at.%, 2.5 mm long Yb: CaGdAlO4 crystal. The average power of laser is 520 mW. It seems this is the highest average power reported for a diode-pumped solid-state sub-100fs laser. It is also observed the efficient generation of a record-large number of spectral sidebands in an active crystal driven by two-color fs pulses. Overall the measured energy conversion efficiency in PbWO4 is as high as 31%. Among the spectral sidebands, the good mutual coherence opens a possibility for the broadband light source to be used to synthesize subfemtosecond light waveforms.
We acknowledge the overall support received from both Indian Institute of Technology. New Delhi and National Physical Laboratory, New Delhi