CC BY
16LS-P-11
The Spectral Properties of Nd-disk Laser with Degenerate Cavity
Configuration.
D.A.Nikolaev1, V.B.Tsvetkov1.
1. Prokhorov General Physics Institute, Russian Academy of Sciences, 38 Vavilov Str., 119991 Moscow,
Russian Federation
nikolaev@lsk.gpi.ru
The goal of the presentation is the demonstration of the possibility of CW TEM00 Nd:YVO4 disk laser with degenerate cavity configuration [1-3] to produce a narrowband emission. Any other mode selection technique was not used. A one- two- or three- point pumping of active disk (AD) was used.
The optical scheme of the laser with degenerate cavity configuration and intracavity beam path is shown on figure 1. The use of off-axis beams and a standing wave in the cavity was the basic demand to the optical schematic. The cavity with the length of 50 mm was formed by a flat HR mirror deposited on the back surface of the active disk, and concave spherical mirror M1 (r=200 mm). Output coupler was formed also in spherical mirror. As an AD the Nd:YVO4 crystal 20x20x0.5 mm3 in sizes and Nd3+-ions concentration of 2.5x1020 cm-3 was used.
Fig.1. Degenerate laser cavity schematic. Fig.2. Fabry-Perot interference patterns of the laser emission.
Dichroic AR coating with high transmission both at pumping and lasing wavelength was deposited on the AD forward surface. Mirror Ml had reflection coefficient R=95 % in a small part of the suface and R>99.8 % was organized in other part of a mirror. This small part of the mirror served as an output coupler for the laser. We used one, two or three pumping points produced by focusing of the emission of three 808-nm diode modules. The pumping points possessed the sizes of about 170 ^m. It corresponded to TEM00 intracavity beam waist. Distances between pumping points were made 5.7 mm. Total pumping power absorbed in AD varied in a range to 15.6 W.
Spectral, power and spatial parameters of the laser were studied. At research of spectral parameters there were used glass (n=1.51) cylindrical Fabry-Perot interferometers (IFP) with reflection coefficient of mirrors R=85 % and bases of 1.18 mm, 3.3 mm, 15 mm and 40 mm. The maximum of optical system resolution was ~6x10-3 cm-1 (~180 MHz).
Results of researches have shown that in all range of pumping power the beam divergence was 2.3±0.23 mrad (FWHM) that corresponded to the calculated value 2.4 mrad for TEM00 lasing. The spectral characteristics of a lasing also did not depend on a pumping power and number of pumping spots. In all cases, the lasing spectrum contained two lines with approximately equal intensity with widths (FWHM) of <6x10-3 cm-1 (<180 MHz) and distance between them of 5x10-2 cm-1 (5 GHz).
In figure 2 it is shown interference patterns of a laser radiation for case IFP with base of 15 and 40 mm. The maximum output power of the laser was 3.2 W.
To explain the nature of the spectrally selective properties of the degenerate resonator, the additional studies were carried out with using the pulsed pumping. The results of it demonstrated that selection of longitudinal modes it is provided at the expense of a several cavity shoulders with different length.
[1] D. Herriott, H. Kogelnik and R. Kompfner, Off-Axis Paths in Spherical Mirror Interferometers, Applied Optics, vol.3, 523-526, (1964).
[2] I. A. Ramsay, J. J. Degna, A ray analysis of optical resonators formed by two spherical mirrors, Applied Optics, vol.9, 385-398, (1970).
[3] A. M. Bul'kanov, D. A. Nikolaev, A. I. Shamatova, I. A. Shcherbakov, V. B. Tsvetkov, Single-mode Nd:GGG laser with three-beam diode pumping and a degenerate cavity, Quantum Electronics, vol.48 (5), 468-471, (2018).
