The MPS configuration can be used with a wide variety of laser crystals and laser diodes to operate at relatively high powers.
Corona MPS Gain Module
The Multipass Slab (MPS) gain module design is a diode-laser, side-pumped configuration that combines high efficiency with high beam quality. Because of a relatively low volumetric thermal loading, the MPS configuration can be used with a wide variety of laser crystals and laser diodes to operate at relatively high powers. Typical MPS gain modules utilize solid state laser crystals such as Nd:YLF, Nd:YVO4, Tm:YLF, Er:YLF, Yb:S-FAP, and Cr:LiSAF.
The general design for a configuration in which the laser crystal is pumped by two offset bars on either side of the crystal is seen in Fig. 1. The crystal is fabricated in the form of a thin rectangular slab. The fast-axis collimated outputs from the diode bar lasers pump the crystal through antireflection (AR)-coated faces, and the opposite faces of the slab are coated to highly reflect any unabsorbed pump light back toward the pump lasers. The challenge to efficiently extract the pump power is met by multi-passing the laser mode through the sheet of gain, by the use of mirrors mounted immediately outside of the AR coated slab end faces.
Figure 1 Schematic of MPS Gain Module
As an example, the majority of MPS designs using Nd:YLF have been configured with opposed, offset pump lasers. Fig. 2 is a photograph of the MPS design implemented in a Gain Module, which includes the laser crystal (typically 28 mm × 6 mm × 2 mm, with c-axis perpendicular to the large face) not visible in the picture, sandwiched between two S-shaped, nickel-plated, water-cooled heat sinks, in the center of the picture. The diode bars are mounted on separate, water-cooled heat sinks. All heat sinks are mounted to a common base, fabricated from a glass-fiber-reinforced plastic that acts as both a cooling water manifold and an electrical insulator for the diode electrical connections. One of the multi-passing mirrors is visible at the end of the lower crystal heat sink.
Figure 2 “Gain Module” implementation of MPS design, showing diode pump lasers, laser crystal heat sink, multipass mirror, all mounted on a fiber-reinforced plastic base that can be TE or water cooled.