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In this study, the optimal condition of a multi-plate birefringent filter (BRF) used in a single-frequency continuous-wave (CW) tunable laser is theoretically and experimentally investigated. The dependence of the optimal condition on the diving angle of the BRF optical axis is first deduced. Based on the proposed optimal condition, the diving angle of the BRF optical axis is optimized to 29.1°. Subsequently, a novel off-axis multi-plate BRF with a thickness ratio of 1:2:5:9 and the thinnest plate of 0.5 mm is designed and utilized in a tunable titanium:sapphire (Ti:S) laser. As a result, the operating wavelength of the Ti:S laser is successfully tuned from 691.48 to 995.55 nm by rotating the BRF 18°. The obtained tuning slope efficiency and maximum tuning range are 16.9 nm/° and 304.07 nm, respectively. The experimental results agree well with the theoretical analysis results, which provide a feasible approach for designing BRFs to satisfy the requirements of other single-frequency CW wideband tunable lasers.

Here, we present a compact Watt-level single-frequency continuous-wave (CW) self-tuning titanium:sapphire (Ti:S) laser, which is implemented using a three-plate Ti:S crystal as both a gain medium and frequency-tuning element. The thickness ratio of the three-plate Ti:S crystal is 1:2:4, of which the thinnest plate measured 1 mm. The optical axes lie on their own surfaces and parallel to each other. Based on the presented self-tuning crystal, a ring resonator is designed and built. The maximum wavelength tuning range of the single-frequency self-tuning Ti:S laser is 108.84 nm, as demonstrated experimentally by rotating the three-plate Ti:S crystal, indicating good agreement with theoretical prediction. To the best of our knowledge, this is the first study to report a single-frequency CW self-tuning Ti:S laser, which can provide a feasible approach for achieving a compact all-solid-state single-frequency CW-tunable Ti:S laser.

Multi-beam laser processing is a very popular method to improve processing efficiency. For this purpose, a compact and stable multi-beam pulsed 355 nm ultraviolet (UV) laser based on a micro-lens array (MLA) is presented in this Letter. It is worth noting that the MLA is employed to act as the spatial splitter as well as the coupling lens. With assistance of the MLA, the 1064 nm laser and 532 nm laser are divided into four sub-beams and focused at different areas of the third-harmonic generation (THG) crystal. As a result, the multi-beam pulsed 355 nm UV laser is successfully generated inside the THG crystal. The measured pulse widths of four sub-beams are shorter than 9 ns. Especially, the generated four sub-beams have good long-term power stability benefitting from the employed MLA. We believe that the generated stable multi-beam 355 nm UV laser can meet the requirement of high-efficiency laser processing, and the presented method can also pave the way to generate stable and long-lived multi-beam UV lasers.