Yb:glass fiber lasers have matured to the point where the average power scaling of such devices to the kilowatt level and beyond can be realistically pursued. In this paper, we present a comprehensive study of thermal, stress, and average power scaling in double-clad silica fiber lasers. We show that careful management of thermal effects in fiber lasers will determine the efficiency and success of scaling-up efforts.

Thermal, stress, and thermo-optic effects in high average power double-clad silica fiber lasers

The design and operation of solid-state Raman lasers

https://hal.archives-ouvertes.fr/hal-00140068/document

On thermal effects in solid state lasers: the case of ytterbium-doped materials

Thermal effects lead to upper limits on the maximum achievable power in end-pumped solid-state laser rods. Thermal fracture is an ultimate limitation on pump power, while optical distortions and depolarization leading to increased losses in the laser resonator tend to yield a lower upper bound on the pump power. The relevant optical distortion profiles and maximum stresses are derived as a function of length-to-diameter ratio and pump spot size. Length-to-diameter ratios up to 1.5 are considered. Edge-cooled and face-cooled active-mirror geometries are analyzed and compared directly. The problem is cast into a nondimensional form so that the results are applicable to arbitrary rod materials. >

Temperature and thermal stress scaling in finite-length end-pumped laser rods

The authors analyze the scaling limits of diode-end-pumped Nd:YAG lasers imposed by pumping geometry, thermal distortion, birefringence, and fracture. A scalable 15-W output power diode-end-pumped laser which achieves a 60% slope efficiency is demonstrated. Thermal distortion in this laser is reduced from 2.6 waves to less than 0.15 waves with an aspheric laser rod. Depolarization is reduced by 40 times to less than 0.2% per pass using optical rotators. Modeling results, which accurately predict thermal distortion and birefringence, imply a thermal fracture-limited output power for short end-pumped rods less than 45 W. A dual rod design for an 80-W device is described. One of the four modules in this device has been assembled and tested, producing a CW output of 22.5 W. >

Scaling CW diode-end-pumped Nd:YAG lasers to high average powers

In order to estimate deleterious effects caused by heating in continuous‐wave end‐pumped solid‐state lasers, the heat equation has been solved for an axially heated cylinder with a thermally conductive boundary at the periphery Steady‐state thermal profiles are developed using both a full numerical solution and an analytic approximation which assumes only radial heat flow The analytic solution, which is in good agreement with the numerical solution, is utilized to obtain an expression for the thermal focusing due to temperature‐induced refractive index changes For Nd:YAG, 1 W of pump power deposited as heat is predicted to cause a thermal focusing length comparable to the cavity length of a typical diode end‐pumped laser

M.E. Innocenzi

Papers

Thermal modeling of continuous‐wave end‐pumped solid‐state lasers

Diode Laser End-Pumped Neoeymium Lasers: The Road to Higher Powers