L. A. W. Gloster

HIGHLY EFFICIENT SINGLE-LONGITUDINAL-MODE BETA-BAB2O4 OPTICAL PARAMETRIC OSCILLATOR WITH A NEW CAVITY DESIGN

A new coupled-cavity design for single-longitudinal-mode operation of an optical parametric oscillator (OPO) is presented. The OPO is based on a beta-BaB(2)O(4) crystal and is pumped by the third harmonic of a Nd:YAG laser. With this design, we achieved single-longitudinal-mode operation of the OPO with a decrease in the threshold and an increase in external efficiency compared with those of a conventional grazing-incidence OPO. A mathematical model that describes the mode spacings for this cavity is given.

Narrow-band β-BaB 2 O 4 optical parametric oscillator in a grazing-incidence configuration

The key operating parameters of a grazing-incidence optical parametric oscillator (GIOPO) based on β-BaB2O4 pumped by the third harmonic of a Nd:YAG laser are studied. The bandwidth of the GIOPO is investigated as a function of both the pump-laser bandwidth and the incident angle on the diffraction grating. The efficiency of the device is investigated by measurement of both the depletion of the pump laser and the output of the GIOPO. The results indicate a strong dependence of the bandwidth of the GIOPO on the bandwidth of the pump laser. A qualitative evaluation is given to explain this dependence.

Diode-pumped Q-switched Yb:S-FAP laser

Abstract A diode-pumped, repetitively Q-switched 1% doped Yb 3+ :Sr 5 (PO 4 ) 3 F laser has been demonstrated for the first time, pumped with a strained InGaAs continuous-wave diode laser. The maximum output energy per pulse was 125 μJ at 1.047 μm, with a pulse duration of sub-30 ns. The Q-switched average power was identical to the steady-state CW power at repetition rates over 1 to 10 kHz, consistent with a 1.26 ms emission lifetime.

Continuous-wave diode-pumped Yb3+:S-FAP laser

Abstract A continuous-wave InGaAs diode-pumped Yb 3+ :S-FAP laser has been demonstrated. We report an output power of 75 mW with a slope efficiency of 78%. Power improvements of up to 2.5 times are reported with crystal cooling.

Efficient, low-threshold collinear and noncollinear beta-barium borate optical parametric oscillators.

The performance of collinear and noncollinear pulsed barium borate optical parametric oscillators with third-harmonic Nd:YAG pumping is analyzed. The effects of tangential phase matching and pump Poynting vector walk-off compensation are shown to enhance noncollinear operation. However, we show that these effects are mutually exclusive for a typeI beta-barium borate optical parametric oscillator and furthermore that tangential phase matching is dominant. The selection of a collinear or a noncollinear configuration is determined by pump divergence and spot size as well as by crystal aperture. With a pump divergence of 4mrad, noncollinear operation is optimal. The highest slope efficiency, 37%, and the lowest threshold, 5mJ, are obtained with nearly perfect tangential phase matching. For a pump divergence of less than 2mrad and a similar spot size, collinear operation gives the lowest threshold, 3.2mJ, and the highest slope efficiency, 33%.

Chromium-doped forsterite: the influence of crystal characteristics on laser performance

A study of the dependence of the gain-switched laser operation of chromium forsterite on crystal parameters is presented. Results are reported for a wide range of chromium (IV) ion concentration: 0.02-0.12 at. % and 12-41 figure of merit, with emphasis on performance of the recently developed material with a dopant level of >0.10 at. %. Threshold and slope efficiency calculations are compared with measured performance for all crystals, with variation of pump polarization and output coupling. With 3% output coupling, the lowest threshold of 1.8 mJ, and highest slope efficiency of 13% were measured for a short, high-dopant-level crystal. With 33% output coupling a slope efficiency of 44% was measured for this crystal. Results demonstrate the considerable potential of short, high-dopant-level crystals for applications such as amplification, diode pumping, and narrow-bandwidth operation.

Noncollinear phase matching in a type I barium borate optical parametric oscillator

Abstract A full characterisation of noncollinear type I phase matching is presented for BaB 2 O 4 OPOs pumped at 532 nm. We demonstrate how increased noncollinearity leads to highly efficient low threshold oscillators. We consider the effects of noncollinearity on signal linewidth and oscillator tuning, with good agreement being found with a theoretical model.

Laser mode selection in multiarm grazing-incidence cavities

A four-arm grazing-incidence cavity (GIC) is demonstrated. It ensures stable single-mode operation in a pulsed laser system by interferometrically enhancing mode selection; the corresponding standard GIC operates on five modes. We show that the four-arm GIC gives the best overall performance in terms of mode selectivity and threshold when compared with the standard GIC or with three-arm GIC’s. In addition, an analysis of the interference effect is detailed that allows the four-arm GIC to be optimized for mode selection. Threshold gain and cavity losses are calculated, and the predicted mode spacing and complex reflectance are experimentally verified.

The role of active ion concentration in tuned chromium forsterite oscillators

We report a comparative study of the tuned oscillator performance of chromium forsterite crystals with a range of crystal characteristics. Emphasis is placed on results obtained for the recently developed high dopant level materials. Tuning range, conversion efficiency and peak emission wavelength are analysed for prism-tuned and Littrow grating cavities. Diagnostic spectral measurements are carried out following second harmonic generation in KTP. Linewidth is measured for the Littrow cavity, and the potential for narrow bandwidth lasers is assessed.

Frequency locking of a pulsed single-longitudinal-mode laser in a coupled-cavity resonator

The performance of a novel resonator that couples a grazing-incidence and a linear cavity is reported. The coupling secures single-longitudinal mode, TEM(00), higher-efficiency and lower-threshold operation. By use of Ti:sapphire as the gain medium, a slope efficiency of 23% and a 100-nm tuning range are reported. A model is explained that fully predicts the mode behavior of the resonator and that can be used to optimize the cavity for single-mode operation. We have developed computer control of the cavity, which is simple in design and is used to lock the <200-MHz bandwidth mode to +/-40 MHz. A 4.8-GHz scan has also been demonstrated.