Improving Diode Pumped Alkali Laser (DPAL) Beam Quality by Inducing Refractive Index Gradients
Abstract
Cs diode pumped alkali lasers (DPALs) have been extensively studied during the last decade. DPALs operating in CW mode absorb and must dissipate appreciable amount of heat. The thermal load concentrated along the optical axis of static Cs DPAL cell results in large temperature, gas density and hence refractive index gradients near the cell optical axis. The refractive index gradients in the laser cell result in wave front aberrations, such as defocusing, similar to thermal lensing in solid state lasers. Wave front distortion of the laser beam affects the beam quality and the potential to be focused to very small spots without excessive divergence. The beam quality can be quantified by the laser beam quality M2. Combining wave optics model and gasdynamic code we have very recently shown [K. Waichman, B. D. Barmashenko and S. Rosenwaks, JOSA B 35, 558 (2018)] that large radial gradients of the refractive index in the heated gain medium lead to improvement of M2. This effect depends on the composition of the buffer gas in the cell. We propose to verify this counterintuitive finding by careful measurements of M2 in Cs static DPALs with different compositions of the buffer gases. Verification of this finding is extremely important to the HEL JTO-Air Force since it may lead to a new, unexpected way, to improve the beam quality of DPALs and thus enable to reduce the far field spot size of the laser beam. In addition to the experimental studies, further calculations using the wave optics model coupled to gas dynamics code will be performed. Such calculations will make it possible to find optimal buffer gas composition, temperature and pump to laser beam overlap corresponding to the best beam quality and maximum light intensity in the far field.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jan 14, 2022
- Source ID
- FA95501917013
Entities
People
- Salman Rosenwaks
Organizations
- Air Force Office of Scientific Research
- Ben-Gurion University of the Negev
- United States Air Force