Tunable Narrowband Tm:YAP Laser using a Transversally Chirped Volume Bragg Grating

Summary form only given. Tunable long wave infrared (LWIR) coherent sources emitting between 8 and 12 μm can be used for versatile remote gas sensing. In ref [1] we implemented a parametric oscillator in which wavelength tunability was achieved by temperature tuning of the crystal indices of refraction. It is well known that a similar wavelength range can be addressed by tuning the pump wavelength rather than the crystal temperature [2]. In addition, pump tuning can be significantly faster than temperature tuning. In this context we also need a narrow band spectrum to control the spectral output of the optical parametric oscillator, which is based on Vernier spectral filtering in doubly-resonant cavities. Seger and his team exhibited single longitudinal mode operation in a microlaser tuned with transversally chirped volume Bragg grating (TC-VBG) near 1 μm [3]. We show how this concept can be applied to a different laser emitting at 2 μm. We designed a Tm:YAP laser with a TC-VBG as output coupler. The cavity, shown in Fig. 1 (a), is composed of a high reflective dielectric concave mirror around 2 gm, a 4 mm long 4 %at. thulium doped a -cut YAP rod and a TC-VBG with 1940 to 1960 nm tuning range, 85 % reflectivity and 0.8 nm bandwidth. We pump the cavity with a 9 W laser diode emitting near 790 nm. Depending on the output wavelength, this laser has a threshold between 1.8 W and 2.1 W and 14 to 17 % of efficiency. With this cavity we obtained a continuous wave laser emitting up to fi ve cavity modes witch gives a 0.2 nm wide spectrum with up to 1.5 W laser output power at 1948 nm under 7 W pumping. Working at low power above the threshold reduces the laser spectral width below 0.1 nm but it quickly reaches 0.2 nm wide (see Fig 1 (b)). We plan to push on to obtain narrower linewidth.