Advanced laser sources for industrial processing and remote sensing

Abstract

In the fifty years since their discovery, the use of laser oscillators and amplifiers has increased to cover a wide range of applications. This thesis develops diode-pumped solid-state (DPSS) lasers for two main applications: industrial processing and remote sensing.

The first half of this thesis investigates the development of bounce geometry lasers that can be used to generate high power light sources suitable for industrial processing using diode-pumped Nd:YVO4 laser sources at both 1342nm and 1064nm transitions. The first of these investigations develops bounce geometry configuration Nd:YVO4 laser sources operating at 1342nm. For continuous wave (CW) operation at powers of 15.9W with 30% optical-to-optical efficiency were achieved. For pulsed operation, Q-switching based on an acousto-optic modulator and mode-locking based on nonlinear-mirror mode-locking were demonstrated.

To suit a range of different industrial applications, a versatile gain switched laser diode source at a wavelength of 1064nm was developed to have independently adjustable pulse energies, pulse duration and repetition rates. To reach a commercially useful power level, a seed laser was amplified in a master oscillator power amplifier (MOPA) configuration using two ultrahigh-gain Nd:YVO4 bounce amplifiers in series. In a first amplifier (preamplifier), a small-signal gain of ~50dB with good TEM00 beam quality preservation was achieved with 24W pumping while a second power amplifier was used to achieve an average output power of up to ~14W using an input seed power of 188mW.

The second part of this thesis develops laser sources for remote sensing applications based on direct diode pumping of Alexandrite lasers in an end-pumping configuration. When compared to Q-switched Nd:YAG lasers, which are typically used for satellite based remote sensing, Alexandrite lasers have the potential to be more efficient and offer more flexible wavelength tunability. Following a broad

overview of Alexandrite lasers, this thesis investigates diode-pumped Alexandrite laser performance. To achieve a high average power, a compact laser cavity was built with output power as high as 26.2W and slope efficiency of 49%. This was more than an order of magnitude higher than previously reported from diode pumped Alexandrite lasers. To achieve TEM00 laser output, many extended cavity designs were investigated.

Following this, to enhance the laser efficiency, an Alexandrite laser was developed utilizing the unique characteristics of temperature-dependent gain of Alexandrite and the performance from 20-150˚C was characterised. To demonstrate high pulse energies, suitable for remote sensing applications, for the first time, a direct diode pumping Q-switched Alexandrite was demonstrated. A Q-switched output pulse energy of >1mJ at 100Hz pulse repetition rate in TEM00 mode was achieved.