Research Index / Ultrafast Optics / Yb-Doped Lasers

 

In collaboration with Patrick George and Frederic Druon at the Institute d'Optic, in France, a regenerative amplifier was demonstrated using Yb-doped GdCOB.  This laser material has a thermal conductivity 3 times higher than that of Yb-doped phosphate glass and an emission cross-section of a similar value.  The chirped pulse amplifier produced 12 mJ pulses compressed to 30 fs. 

Yb-doped KYW is a laser crystal that exhibits an emission cross-section considerably larger than the Yb-phosphate glass and the GdCOB used in previous experiments.  Furthermore, by using a minor axis for pumping and lasing a broader, smoother spectrum can be made to lase.  In an end-pumped configuration, the KYW crystal produced a slope efficiency of 40% and a cw output of 680 mW from an incident pump of 2.8 W.  As a regenerative amplifier this laser produced 50 J pulses at 2 kHz repetition rate.  Compressed, 40 mJ pulses measured 400 fs in duration.  Using the same pumping configuration and reconfiguring the cavity to include dispersion compensation, Kerr-lens mode-locking laser was obtained.  This is the first diode-pumped rare-earth laser to be mod-locked without a semiconductor saturable absorber.  It displays a pulse duration ranging from 71 to 105 fs. 

65-J pulses were obtained from a side-pumped version of this laser at 2 kHz using a 20 W diode bar.  Autocorrelation indicates these pulses have 460-fs duration.  In similar experiments Yb-doped KGW was used as a gain material in a regenerative amplifier, but with the primary axis being excited (E//a).  In this laser a 43% slope efficiency was seen in cw operation and 43 J pulses were obtained at a repetition rate of 1 kHz.  Raman activity was also observed in this system.  Finally, a high-energy regenerative chirped-pulse amplifier was demonstrated using a flashlamp-pumped Ti:sapphire laser as a source to simulate diode pumping with up to 1.2 J.  The slope efficiency of the laser was as high as 72% in free-running mode, without polarizer or electro-optic cell.  As a chirped-pulse amplifier, the laser produces 25 mJ compressed to 1.4 ps pulse limited by gain narrowing.  The following table summarizes the characteristics of several Yb-doped lasers demonstrated during the last two years at CUOS.

Amplifier Keystone- shaped QX/Yb Diode-end- pumped Yb:KYW Diode-side- pumped Yb:KYW Diode-end- pumped Yb:KGW Ti:sapphire- pumped Yb:KGW
Pump polarization N/A E// E// E// E//
Pump wavelength (nm) 970-975 94 98 94 93
Signal polarization N/A E// E// E// E//
Max. pump at gain medium 36 W (avg) qcw 2.8 W cw 16.5 W cw 2.6 W cw 1.27 J pulsed
Max. free- running output 4.3 W (avg) qcw 680 mW 1 W 660 mW 0.62 J pulsed
Pulse energy before compression (J) 150 6 9 6 2500
Compressed pulsewidth, assuming Gaussian (fs) 20 40 46 39 100
Highest rep. rate, limited by 150 Hz, thermal 2000 Hz, P.C. driver 2000 Hz, P.C. driver 2000 Hz, P.C. driver 1 Hz, pump laser


Research Index / Ultrafast Optics / Yb-Doped Lasers

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