Low-cost 7 mW CW 355-nm diode-pumped intracavity frequency-tripled microchip laser

Oxxius 355 nm CW UV microchip laser sources today

This 2006 SPIE paper introduces the first efficient 355 nm CW UV microchip laser based on diode-pumped intracavity frequency tripling, a monolithic architecture that eliminated the birefringence interference issues that had previously prevented reliable CW UV output from solid-state sources. By optically contacting the Nd:YVO4 gain crystal with KTP and LBO nonlinear crystals, the authors produced a fully monolithic cavity requiring no alignment, with inherently single-frequency operation and significantly reduced manufacturing cost compared to prior UV laser designs.

At the time of this publication, CW UV lasers at 355 nm were limited to excimer and gas ion sources, bulky, power-hungry and expensive systems with wall-plug efficiencies below 0.01%. The compact diode-pumped approach demonstrated here changed the landscape by showing that milliwatt-scale 355 nm output was achievable from a microchip-scale cavity with a fraction of the electrical consumption. The monolithic structure, obtained by optical contacting rather than mechanical clamping, also delivered the mechanical and thermal stability needed for instrument integration.

Applications driving 355 nm UV laser adoption

The 355 nm wavelength addresses a broad range of demanding analytical applications. In life science, it is the standard excitation line for DAPI and Hoechst nuclear stains in fluorescence microscopy, and for BUV polymer dyes in high-dimensional flow cytometry. In semiconductor manufacturing, it is used for wafer inspection, photomask review, and UV lithography alignment, applications where low noise and stable CW output are non-negotiable. The monolithic intracavity tripling approach demonstrated in this paper laid the foundation for all of Oxxius’s subsequent 355 nm laser development, and the principles described here remain directly applicable to the LBX-355 and related UV sources currently in production.

Abstract

Low noise CW milliWatt scale UV lasers are needed for many analysis applications in the semiconductor and the biological fields. Intracavity tripling has been widely used to improve the UV output power of Q-switched or modelocked lasers, but no efficient diode-pumped CW UV laser was ever reported. One of the key to success is the use of a monolithic laser structure which both eliminates the birefringence interference issue and facilitates the single frequency operation. The monolithic structure is obtained by optically contacting crystals. It does not require any alignment, reduces the manufacturing cost and improves reliability. The optimization of the amplifying medium and doubling and tripling crystals involves as many parameters as pump absorption, thermal lens, cavity length, 1064 nm mode size, walk-off, acceptance angles, polarizations, phases… The interplay between these parameters will be …