laser DPSS

This page describes the conversion of a simple, inexpensive green laser pointer into a lab-grade laser. The heart of this DPSS laser is an inexpensive green laser pointer. Such pointers are actually diode-pumped solid-state (DPSS) lasers consisting of a small vanadate (Nd:YVO4) laser (operating at 1064nm) pumped by an 808nm diode laser and frequency
laser DPSS - schematic

doubled to produce 532nm output. The actual vanadate crystal and KTP frequency doubling crystal, along with the HR and OC mirrors, are built as a small one-piece composite unit under 5mm in length. Radiation from the pump diode (at 808nm) passes through the HR to pump the vanadate (the HR is a wavelength-selective coating which transmits 808nm while reflecting 1064nm). [1] A close-up of a green laser pointer DPSS as seen through a microscope. The vanadate and KTP crystals are constructed as a single unit with the HR and OC reflectors deposited directly on the surfaces of the optical components. The assembly is pumped directly from a diode (usually around 200mW output at 808nm) which passes through the HR. There are two basic problems with a simple laser such as this: the wavelength of the pump diode varies with temperature, and the phase-matching characteristics of the KTP doubling crystal also varies with temperature. In the case of the pump diode, all diodes behave in a similar manner with wavelength shifting towards longer IR wavelengths as temperature increases (of course, as drive current increases, temperature does as well). Unfortunately, vanadate (as well as YAG, and other neodymium laser host glasses) has sharp absorption peaks as so allowing the pump wavelength to vary over a span of a few nanometers can move the wavelength from one of great absorption to one of less absorption resulting in a decrease in output...

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