Compact active mirror laser (CAMIL)

Abstract

This work presents concept and scaling considerations for a solid-state laser with a gain medium disk operating in the active mirror mode. The disk is of composite construction formed by bonding undoped optical medium to the peripheral edges of a gain medium disk. Pump diode anays are placed around the perimeter of the composite disk and pump light is injected into the undoped edge. With proper choice of lasant doping, diode placement and diode divergence, a uniform laser gain can be achieved across large portions of the disk. To mitigate thermal deformations, the gain medium disk is pressure-clamped to a rigid, cooled substrate. Effective reduction of thermo-optical distortions makes this laser suitable for operation at high-average power.Keywords: solid-state lasers, disk laser, active mirror, ytterbium, beam quality DISK-TYPE SOLID-STATE LASERSSolid-state lasers (SSL) scalable to high-average power (HAP) are highly desirable for many government and commercial applications. The key challenges to developing HAP SSL are thermomechanical effects, which occur in the gain medium as a result of pumping. Even with pumping by the efficient semiconductor laser diodes, significant portion of the pump energy is dissipated into heat, which is deposited into the SSL medium. This causes thermal lensing, mechanical stresses, and other effects, with likely consequences of degraded beam quality (BQ), reduced laser power, and possibly a fracture of the SSL medium. Beam quality is particularly affected by temperature gradients perpendicular to laser beam axis. Popular SSL configurations, such as rods or slabs, are particularly susceptible to such thermal effects. Despite ingenious designs that recently appeared, attempts to further increase average power output from rod and slab lasers drive the design toward regimes of increased complexity, reduced electric efficiency, and worsening BQ.Disk-type SSLs enjoy inherently low susceptibility to thermo-optical distortions and have demonstrated lasing at HAP with outstanding beam quality [1 -3]. Their large, round aperture reduces diffraction and beam clipping losses experienced by other SSL canfigurations. In a disk laser, transverse temperature gradients are reduced because waste heat is extracted from the gain medium in the direction parallel to laser beam axis. A disk laser may use transmissive disks shown in Figure la or reflective disks shown in Figure lb. In a transmissive disk, waste heat is removed by gas flowing through the optical path. In a reflective disk, also known as active mirror amplifier (AMA), the back surface of the disk is available for liquid cooling, which is more efficient than gas cooling and well suited for continuous operation at HAP.

<title>Solid-state high-energy laser</title>

“…The resulting SSHEL is sufficiently lightweight and compact for integration onto a medium-size land vehicle, Figure 9. Additional improvements are expected with the use of side-pumped CAMIL [7].…”

“…In either case, the substrate acts as a 'backbone' that mitigates thermal deformations of the disk. Pump radiation is injected into the disk either through one of the large faces (face pumping, Figure 4a) [6] or through the peripheral edge (side pumping) [7]. Face-pumped CAMIL using Nd:YAG, Nd:GGG, Nd:glass, or Yb:S-FAP gain medium disks can be integrated into compact modules, which can be used to construct laser amplifiers and oscillators.…”

High-gain multipassed Yb:YAG amplifier for ultrashort pulse laser

“…We have previously reported on a reflective disk laser with an alternative edge-pumped configuration [10][11][12][13][14] as shown in Figure 4 which overcomes many challenges associated with a face-pumped Ybbased disk laser. The original concept for a composite laser disk edge-pumped by flashlamps was also invented by Chernoch [15].…”

Erbium-based gas-cooled disk laser

“…Diode power is injected into the perimetral edge and channeled into the lasing (central) portion of the disk where it is gradually absorbed. Superposition of diode beamlets is balanced by absorption in the disk to provide uniform gain over the entire lasing volume [11,12]. The edge-pumped disk laser was test-verified in a DARPA-funded project, which showed that 96% pump uniformity is achievable under realistic conditions [13].…”