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Diode pumped solid state (DPSS) lasers are solid-state lasers made by pumping a solid gain medium, for example, a ruby or a YAG laser crystal, with a laser diode.
The most common DPSS laser in use is the 532 nm wavelength green laser pointer. A powerful (>200 milliwatt) 808 nm wavelength infrared laser diode pumps a neodymium doped yttrium orthvanadate (Nd:YVO4) crystal which produces 1064 nm wavelength light. This is then frequency doubled using a nonlinear optical process in a KTP crystal, producing 532 nm light.
DPSS lasers have advantages in compactness and efficiency over other types, and high power DPSS lasers have replaced ion lasers and flashlamp-pumped lasers in many scientific applications.
Coupling
The frequency of the laser diodes is tuned by means of temperature to produce an optimal compromise between the absorption coefficent in the crystal and energy efficiency (low as possible pump photon energy). As waste energy is limited by the thermal lens this means higher power densities compared to high-intensity discharge lamps.
High power lasers use a single crystal, but many laser diodes, arranged in strips (multiple diodes next to each other in one substrate) and stacks (stacks of substrates). This diode grid can be imaged onto the crystal by means of a lens. Higher brightness (leading to better beam profile and longer diode lifetimes) is achieved by optically removing the dark areas between the diodes, which are needed for cooling and delivering the current. This is done in two steps:
- The "fast axis" is collimated with an aligned grating of cylindrical micro-lenses.
- The partially-collimated beams are then imaged at reduced size into the crystal. The crystal can be pumped longitudinal from both end faces or transverse from three or more sides.
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