CC BY
21LS-P-8
Investigation of Q-switch mode-locking lasing regime in Yb:YAG
disk laser with SWCNT.
D. Guryev1, D. Nikolaev1, N. Arutyunyan1, E. Obraztsova1, V. Tsvetkov1
1 - Prokhorov General Physics Institute of the Russian Academy of Sciences e-mail address: [email protected]
Compact ultrashort pulsed lasers are interesting for diverse application areas. Particularly, lasers based on Yb3+-doped crystals possess advantages over those in other materials [1]. There are a number of publications devoted to waveguide Yb-lasers, operating in Q-switch or ultrashort pulses lasing mode with saturable absorbers [2]. However, the waveguide fabrication is a complex and expensive procedure. So a competitive idea with the use of disk lasers is interesting also. Disk lasers are widely used for creation of high-power laser systems with high quality of output radiation. Small thickness of disk active medium allows to avoid influence of thermooptical effects. In addition, the small thickness of an active element allows to make the cavity length rather small that the fundamental frequency pulse repetition rate is at the GHz level.
Application of a waveguide result in self-starting lasing in a mode-lock regime in most case. The question is what will be with disk active medium and carbon nanotubes as saturable absorber.
In present publication we demonstrate Yb:YAG disk laser with single wall carbon nanotubes (SWCNT) as saturable absorber and investigate its operation with different cavity length - 6 cm (2.5 GHz), 90 cm (166 MHz).
Fig.l. The schematic configuration of the passively Q-switched mode-locked Yb:YAG laser with the SWCNT-SA. Dashed line shows
positions of output coupler in cavities of different length.
The active disk thickness was 0.77 mm. The pumping was realized at 940 nm with the pigtailed laser diode. The pumping emission was focused in active disk through concave HR mirror. The output coupler was plane and wedge-shaped with reflection coefficient R=70% at the lasing wavelength. We used SWCNT being prepared by CoMoCat method as the saturable absorber. SWCNT was incorporated in a polymer film and positioned on the plane reflection surface of the output coupler.
In both cases (with both cavity length) the Q-switch mode-lock (QSML) lasing was observed. In the 90 sm cavity, the duration of the Q-switch envelope was 1 - 5 microsecond, depending on the pump power. Maximum average power - 140 mW at 8 W of absorbed pump power. The Q-switch mode-locked pulses followed at a frequency of 166 MHz. In the 6 cm cavity, the duration of the Q-switch envelope was 100 ns. Maximum average power - 90 mW at 8 W of absorbed pump power. The Q-switch mode-locked pulses followed at a frequency of 2.5 GHz.
It is possible that the self-starting mode-locking in waveguide lasers is determined both the saturable absorber and nonlinear effects in a waveguide. So, the main question is how to organize the self-starting operation of disk laser.
Acknowledgments: The reported study was funded by RFBR, project number 18-29-19113.
[1] Sun Young Choi, Thomas Calmano, Fabian Rotermund, Christian Krankel, 2-GHz carbon nanotube mode-locked Yb:YAG channel waveguide laser, Optics Express 26, 5140 (2018)
[2] Ji Eun Bae, Sun Young Choi, Christian Krankel, Kore Hasse and Fabian Rotermund, Evanescent-field Q-switched Yb:YAG Channel Waveguide Lasers with Single- and Double-pass Pumping, Current Optics and Photonics 5, 180 (2021)
