C. Bollig

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.

Power and energy scaling of a diode-end-pumped Nd:YLF laser through gain optimization

An end-pumped Nd:YLF laser was demonstrated, which delivered 60.3 W continuous-wave and more than 52 W Q-switched average power for all repetition rates from 5 to 30 kHz. To achieve this, an analytical solution to estimate and optimize the unsaturated gain in an end-pumped laser gain medium was derived. The approach presented here should open up the route for scaling end-pumped lasers to even higher power and energy levels.

Estimation of thermal fracture limits in quasi–continuous–wave end–pumped lasers through a time–dependent analytical model

A time-dependent analytical thermal model of the temperature and the corresponding induced thermal stresses on the pump face of quasi- continuous wave (qcw) end-pumped laser rods is derived. We apply the model to qcw diode-end-pumped rods and show the maximum peak pump power that can be utilized without fracturing the rod. To illustrate an application of the model, it is applied to a qcw pumped Tm:YLF rod and found to be in very good agreement with published experimental results. The results indicate new criteria to avoid fracture when operating Tm:YLF rods at low qcw pump duty cycles.

330 mJ single-frequency Ho:YLF slab amplifier

We report on a double-pass Ho:YLF slab amplifier which delivered 350 ns long single-frequency pulses of up to 330 mJ at 2064 nm, with a maximum M2 of 1.5 at 50 Hz. It was end pumped with a diode-pumped Tm:YLF slab laser and seeded with up to 50 mJ of single-frequency pulses.

Ho:YLF pumped HBr laser

A Ho:YLF laser pumped HBr molecular laser was developed that produced up to 2.5 mJ of energy in the 4 micron wavelength region. The Ho:YLF laser was fiber pumped using a commercial Tm:fibre laser. The Ho:YLF laser was operated in a single longitudinal mode via injection seeding with a narrow band diode laser which in turn was locked to one of the HBr transitions. The behavior of the HBr laser was described using a rate equation mathematical model and this was solved numerically. Good agreement both qualitatively and quantitatively between the model and experimental results was obtained.

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.

Laser beam propagation characteristics of incoherently added diode bars

The second moment method of laser beam propagation allows for the calculation of the beam quality factor for any laser beam, or combination of laser beams. When several laser beams are added, their effective beam quality factor is not simply the sum of the individual beam quality factors, that is, it does not act as a linear operator. In this paper we derive an analytical expression for the beam quality factor of incoherently added laser beams whose centroids are not collinear. We illustrate the versatility of the final result by showing how this may be applied to the problem of the laser beam propagation characteristics of high power diode bar stacks.

Investigating Thermal Stresses in Quasi-CW Pumped Tm:YLF Laser Crystals

Time dependant thermally induced stresses in an end-pumped Tm:YLF laser rod are investigated numerically. The variation of the maximum incident pump power at the fracture point with respect to pulse length is investigated.

High average power Q-switched 1314 nm two-crystal Nd:YLF laser

A 1314 nm two-crystal Nd:YLF laser was designed and operated in both CW and actively Q-switched modes. Maximum CW output of 26.5 W resulted from 125 W of combined incident pump power. Active Q-switching was obtained by inserting a Brewster-cut acousto optic modulator. This setup delivered an average power of 18.6 W, with a maximum of 5.6 mJ energy per pulse with a pulse duration of 36 ns at a pulse repetition frequency of 500 Hz.

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.