High-energy diode-pumped alexandrite amplifier development with applications in satellite-based lidar

Abstract

Efficient, wavelength-tunable diode-pumped alexandrite laser systems offer the potential for a more versatile, satellite-based lidar source compared to fixed wavelength Nd:YAG systems and non-space compliant lamp-pumped alexandrite. In this paper, we develop a strategy to enable the high-energy operation required for atmospheric lidar based on an efficient diode-pumped Master-Oscillator Power-Amplifier (MOPA) system design. A novel multi-pass 'diamond' slab amplifier geometry is introduced alongside the experimental results of the world's first diode-pumped alexandrite amplifier producing a gain of 2.13 in a demonstration system. A diode-pumped Q-switched alexandrite oscillator is presented with a record-highest pulse energy of 3.80 mJ. Detailed optimisation of a two-stage amplifier design is studied numerically and maximised with temperature, wavelength and pump pulse duration to produce 50 mJ pulse energy. This forms part of an optimised alexandrite MOPA design capable of high pulse energy, showing the future potential of diode-pumped alexandrite for satellite-based atmospheric lidar.

High-energy Q-switched Nd:YAG oscillator and amplifier development for large-mode, low-alignment sensitivity applications

“…Unlike end-pumped rod amplifiers, side-pumped systems avoid the need for tightly controlled pump beam sizes. Many slab amplifier geometries exist, such as the bounce geometry [12], COFFIN [13] and the more recent diamond geometry [4]. For high gain materials such as Nd:YAG with mid-level absorption coefficients (around 10.7 cm −1 [8]), a common geometry is the zig-zag geometry.…”

“…There are many dynamic mechanisms which affect stored inversion, such as ESA, ground state absorption and spontaneous emission. Whilst ESA at the pump wavelength can be significant in materials such as Alexandrite [4], it is not a significant loss mechanism for Nd:YAG pumped at 808 nm. Given this, the stored inversion within the amplifier can be described by…”

“…For decades, neodymium yttrium aluminium garnet (Nd:YAG) has been used to produce long-range high-energy laser systems within defence and space-based metrology. Nd:YAG has dominated space-based satellite systems [1][2][3], although future work is underway to develop more versatile tunable laser systems [4].…”

“…Recent work within diode-pumped MOPA design [4] has outlined methods for amplifier simulation and optimisation. For complex vibronic laser materials, amplifier optimisation requires an analysis of both thermal and spectral based effects, often dependent on excited state absorption (ESA) and lifetime.…”

Ground-based general purpose Doppler-lidar: a technology for Doppler-aerosol measurements and beyond

“…The advantage of a MOPA system is the control of the spectral and spatial properties in an oscillator with lower thermal and optical load on the components and a separated power amplification with little influence on the latter properties. First attempts for an amplifier based on diode-pumped alexandrite are reported [23], showing the possibility for an energy-scaling, though suffering from significant loss of beam quality.…”