Widely-Tunable Dual-Wavelength Tm:YLF, Tm:LuAG, and Tm:YAG Lasers

Abstract

Dual-wavelength operation of lasers are attractive for many applications such as coherent terahertz wave generation, ultrahigh pulse repetition rate creation by optical beating, and laser ranging. Several methods could be employed for achieving multicolor laser operation including usage of specially coated cavity optics, employment of dual laser crystals, utilization of coupled cavities, and deployment of Fabry-Perot band-pass filters or volume Bragg gratings. Most of the time, these approaches provide multicolor laser operation at a single wavelength pair, and laser power in each line might fluctuate with experimental conditions (such as crystal temperature and pump power variations). In recent years, usage of intracavity birefringent filters (BRFs) was proposed as a flexible method for the generation of multicolor laser operation [1–4]. Advantages of BRFs in multicolor lasing include: (a) low cost, (b) simple operation, (c) one BRF plate empowering multicolor laser operation in many different wavelength pairs, (d) capability to control laser power in each line, (e) ability to use a rich number of filter parameters from a single BRF plate, (f) effectiveness in continuous-wave, gain-switched, Q-switched and cw mode-locked regimes, and (g) universal usage of the device in any laser that lies within the transmission bandwidth of the BRF plate. In our earlier work, we have employed a 3-mm thick, off-surface optic axis crystalline quartz BRF with an optic axis 45° to the surface of the plate to generate two-color cw laser operation in 11 and 10 different transition combinations in Cr:Nd:GSGG and Cr:LiSAF [3], respectively. In this study [5], we have demonstrated that the same BRF plate could also be used for multicolor laser operation of solid-state lasers around 2 μm. Optimization of the rotation angle of the intracavity inserted BRF plate around different orders (rotation angles) facilitated two-color laser operation in 11, 12 and 8 different wavelength pairs in Tm:YLF, Tm:LuAG and Tm:YAG, respectively [5]. For most of the cases, fine tuning of the BRF rotation angle enabled adjustment of laser power in each line. Figure 1 (a) shows sample optical spectra for Tm:YLF, and Fig. 1 (b) demonstrates details of cavity dynamics for synchronous dual-wavelength operation of Tm:YLF at 1868 & 1991 nm pair. To our knowledge, this is the first report of multicolor laser operation in Tm:LuAG and Tm:YAG, and first results with a BRF in Tm:YLF [6]. Moreover, the demonstrated wide-tunability of two-color laser wavelengths is quite rare in literature.