G. M. Thomas

High efficiency >26 W diode end-pumped Alexandrite laser

We show for the first time that multi-ten Watt operation of an Alexandrite laser can be achieved with direct red diode-pumping and with high efficiency. An investigation of diode end-pumped Alexandrite rod lasers demonstrates continuous-wave output power in excess of 26W, more than an order of magnitude higher than previous diode end-pumping systems, and slope efficiency 49%, the highest reported for a diode-pumped Alexandrite laser. Wavelength tuning from 730 to 792nm is demonstrated using self-seeding feedback from an external grating. Q-switched laser operation based on polarization-switching to a lower gain axis of Alexandrite has produced ~mJ-pulse energy at 1kHz pulse rate in fundamental TEM(00) mode.

Passively Q-switched Nd:YVO 4 laser with greater than 11W average power

This paper presents the highest average power passively Q-switched Nd:vanadate laser, to the best of our knowledge. A maximum average output power greater than 11 W was demonstrated using a Nd:YVO4 bounce geometry laser operating at 1064 nm in TEM00 mode, with a spatially stigmatic design. Pulse energies greater than 58 µJ and peak powers in excess of 1.9 kW were obtained; the maximum repetition rate recorded was 190 kHz, close to the upper limit achievable with Cr4+:YAG saturable absorbers.

Diode-pumped Alexandrite lasers in Q-switched and cavity-dumped Q-switched operation

We present the first study of Q-switched Alexandrite lasers under continuous-wave diode-pumping with operation up to 10 kHz repetition rates in TEM00, with spatial quality M2 1.15. With a pulsed-diode dual-end-pumped design, pulse energy is scaled to a record level of 3 mJ. We also demonstrate, for the first time, cavity-dumped Q-switching of diode-pumped Alexandrite lasers under continuous-wave and pulsed diode-pumping, up to 10 kHz. Pulse energy of 510 μJ is demonstrated with 3 ns pulse duration and 170 kW peak power, in TEM00 with M2 < 1.2. Second harmonic generation of the cavity-dumped Q-switched pulses was used to generate UV wavelength 379 nm with conversion efficiency of 47%.

Investigation of a versatile pulsed laser source based on a diode seed and ultra-high gain bounce geometry amplifiers

We present an investigation of a versatile pulsed laser source using a low power, gain-switched diode laser with independently variable repetition rate and pulse duration to seed an ultra-high gain Nd:YVO4 bounce geometry amplifier system at 1064nm. Small-signal gain as high as 50dB was demonstrated in a bounce geometry pre-amplifier from just 24W pumping, with good preservation of TEM00 beam quality. The single amplifier is shown to be limited by amplified spontaneous emission. Study is made of further scaling with a second power amplifier, achieving average output power of ~14W for a pulsed diode seed input of 188μW. This investigation provides some guidelines for using the bounce amplifier to obtain flexible pulse amplification of low-power seed sources to reach scientifically and commercially useful power levels.

Nonlinear mirror modelocking of a bounce geometry laser

We present the investigation of nonlinear mirror modelocking (NLM) of a bounce amplifier laser. This technique, a potential rival to SESAM modelocking, uses a nonlinear crystal and a dichroic mirror to passively modelock a Nd:GdVO(4) slab bounce amplifier operating at 1063nm. At 11.3W, we present the highest power achieved using the NLM technique, using type-II phase-matched KTP, with a pulse duration of 57ps. Using type-I phase-matched BiBO, modelocking was achieved with a shorter pulse duration of 5.7ps at an average power of 7.1W.

Diode-side-pumped Alexandrite slab lasers

We present the investigation of diode-side-pumping of Alexandrite slab lasers in a range of designs using linear cavity and grazing-incidence bounce cavity configurations. An Alexandrite slab laser cavity with double-pass side pumping produces 23.4 mJ free-running energy at 100 Hz rate with slope efficiency ~40% with respect to absorbed pump energy. In a slab laser with single-bounce geometry output power of 12.2 W is produced, and in a double-bounce configuration 6.5 W multimode and 4.5 W output in TEM00 mode is produced. These first results of slab laser and amplifier designs in this paper highlight some of the potential strategies for power and energy scaling of Alexandrite using diode-side-pumped Alexandrite slab architectures with future availability of higher power red diode pumping.

Multi-Watt diode-pumped alexandrite laser operation

We present results of breakthrough multi-Watt diode-pumped Alexandrite laser operation with high efficiency and high pulse energy, showing that this technology could have wide applicability as a compact high power tunable and /or ultrafast laser source.

Wavelength Tunable Passively Q-Switched Alexandrite Laser with Direct Diode-Pumping at 635 nm

We report on a wavelength tunable passively Q-switched Alexandrite laser directly red-diode-pumped at 635 nm. Passive Q-switching was achieved with a semiconductor saturable absorber mirror (SESAM) and wavelength tuning with a birefringent tuner. The pulse repetiton rate was variable on the pump power and wavelength and a maximum 27 kHz rate was achieved in fundamental TEM00 mode. The maximum average output power obtained was 41 mW. The Q-switched wavelength tuning band was studied between 740 nm and 755 nm. To the best of our knowledge, this is the first time that tunable TEM00 passive Q-switched operation of a diode-pumped Alexandrite laser has been achieved. The results obtained in this study can be significantly further optimised for performance. A new cavity configuration for this optimisation is described. Future work is expected to lead to the development of higher power, more efficient tunable passive Q-switched (and potentially passive mode-locked) diode-pumped Alexandrite laser sources in the near-infrared band and also ultraviolet region through frequency conversion.

Diode-pumped alexandrite laser — A new prospect for remote sensing

Tunable-wavelength diode-pumped Alexandrite laser operation includes highest power > 26W (end-pumped rod); > 12W (side-pumped slab); and first Q-switched operation with pulse energy ~ 1mJ at kHz repetition rate, as development for space lidar application.

High average power, passively Q-switched stigmatic bounce geometry laser

Passive Q-switching of lasers can be a simple and effective way to achieve high power pulses. At 1064nm, Cr4+:YAG has been widely implemented as a passive Q-switch [1], however, the average output power of such lasers has largely been limited to ∼1W. In this work, we demonstrate passive Q-switched laser operation to > 11W, the highest average power ever achieved at 1064nm with Cr4+:YAG saturable absorber, to the best of our knowledge.