Mjd Esser

Ho:YLF & Ho:LuLF slab amplifier system delivering 200 mJ, 2 µm single-frequency pulses

A single-frequency single-pass amplifier based on Ho:YLF and Ho:LuLF in a scalable slab architecture delivering up to 210 mJ at 2064 nm is demonstrated. The amplifier was end-pumped by a 1890 nm Tm:YLF slab laser and was seeded with a 69 mJ single-frequency Ho:YLF ring laser operating at 50 Hz.

High-power diode-pumped Tm:YLF slab laser

Recently, there has been an increased interest in high-power and high-energy 2-µm lasers, due to a number of potential medical, military and scientific applications. Our aim is to develop a high-power Tm:YLF slab laser which can be utilized to pump a Ho slab laser. A 68 W Tm:YLF slab laser was recently presented in [1] pumped from one end by a single 6-bar stack delivering ∼300 W of pump power. In this work, we present a Tm:YLF slab laser pumped by two diode-bar stacks from both ends, leading to a maximum output power of 192.5 W.

Comparative study of thermal lensing in low-doped Nd:YVO 4 and Nd:GdVO 4 of equal doping concentration

Nd:GdVO4 is a relatively new laser material with spectral properties very similar to those of Nd:YVO4. It was initially reported that it had almost twice the thermal conductivity of Nd:YVO4, and therefore was said to reduce negative thermal effects. Sato and Taira [1] recently re-measured the thermal conductivity and its temperature dependency and found that it was significantly lower than that of Nd:YVO4. They also reported that dn/dT in the higher gain π-polarisation of Nd:YVO4 is 7.92 at 1064 nm, compared to 10.1 for Nd:GdVO4. One would therefore expect that Nd:YVO4 would have weaker thermal lensing, since it is influenced by both the thermal conductivity and dn/dT. To our knowledge, a direct comparison of the thermal lens of the two materials has never been performed with equal doping concentrations and dimensions. Therefore, we aimed to compare the two materials directly under diode-end-pumping by performing thermal lens measurements during lasing with a HeNe probe beam using identical low-doped (0.15%), 4×4×18 mm3 crystals. Our setup was such that we could separately analyse the dioptric powers in the σ and π polarisations.

Compact fibre-laser-pumped Ho:YLF oscillator-amplifier system

Ho:YLF is an attractive laser material for 2 µm high energy sources since it has a much longer upper laser level lifetime (∼14 ms) and higher emission cross section than Ho:YAG. In addition, the very weak thermal lens on the σ-polarisation helps to deliver diffraction limited beams even under intense end-pumping. However, Ho:YLF has a somewhat stronger quasi-three-level nature, which implies that in order to reach transparency at the 2065 nm line, 22% of the Ho ions need to be pumped into the upper laser level (at room temperature), but it already reaches transparency at the 1940 nm pump wavelength with only 56% of the Ho ions in the upper laser level. In addition, the pump absorption cross section at 1940 nm is relatively low and strongly polarised. Therefore, the laser design requires a trade-off between efficient pump absorption and low laser threshold.

High-power end-pumped Nd:YLF laser without lifetime quenching

In this paper, we demonstrate the power scaling of an end-pumped Nd:YLF laser to compensate for the astigmatic thermal lens and Q-switched laser performance without any sign of lifetime quenching is presented.

Numerical optimisation of a high-energy end-pumped Ho:YLF slab amplifier

Single frequency 2µm sources are useful in varied applications including remote sensing, spectroscopy and nonlinear conversion to the mid-infrared. However, to generate high energy pulses from a 2 µm oscillator is challenging, which is typically overcome by implementing a master oscillator power amplifier approach [1]. We have previously demonstrated a single frequency Ho:YLF laser which produced up to 70 mJ per pulse [2] at 2064nm and subsequently developed a 200W Tm:YLF slab laser to be used as pump source for a power amplifier.

An HBr oscillator-amplifier pumped by a high-energy Ho:YLF laser system

Laser output in the mid-infrared can be generated by starting from a diode-pumped Tm-doped solid-state laser or fibre laser at 1.9 µm, pumping a Ho-doped system at 2 µm to subsequently pump a non-linear device such as an optical parametric oscillator. For high-energy operation, optically pumped molecular lasers are attractive alternatives due to the potential to scale to very high pump energies without optical damage to the medium. One such example is an HBr laser for which the highest reported output energy was 2.5 mJ in a 132 ns pulse at 50 Hz repetition rate when pumped with a narrow-band Ho:YLF laser [1].