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In this paper, we analyse the prospects for using nitrogen-vacancy centre (NV) containing diamond as a laser gain material by measuring its key laser related parameters. Synthetic chemical vapour deposition grown diamond samples with an NV concentration of ~1 ppm have been selected because of their relatively high NV concentration and low background absorption in comparison to other samples available to us. For the samples measured, the luminescence lifetimes of the NV- and NV0 centres were measured to be 8±1 ns and 20±1 ns respectively. The respective peak stimulated emission cross-sections were (3.6±0.1)×10-17 cm2 and (1.7±0.1)×10-17 cm2. These measurements were combined with absorption measurements to calculate the gain spectra for NV- and NV0 for differing inversion levels. Such calculations indicate that gains approaching those required for laser operation may be possible with one of the samples tested and for the NV- centre

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A monolithic diamond Raman laser is reported. It utilizes a 13-mm radius of curvature lens etched onto the diamond surface and dielectric mirror coatings to form a stable resonator. The performance is compared to that of a monolithic diamond Raman laser operating in a plane-plane cavity. On pumping with a compact Q-switched laser at 532 nm (16 μJ pulse energy; 1.5 ns pulse duration; 10 kHz repetition-rate; M²<1.5), laser action was observed at the first, second, and third Stokes wavelengths (573 nm, 620 nm and 676 nm, respectively) in both cases. For the microlens cavity, a conversion efficiency of 84% was achieved from the pump to the total Raman output power, with a slope efficiency of 88%. This compares to a conversion efficiency of 59% and a slope efficiency of 74% for the plane-plane case. Total Raman output powers of 134 and 96 mW were achieved for the microlens and plane-plane cavities, respectively.

The variation in the Raman gain coefficient in single-crystal diamond for pump wavelengths between 355 and 1450 nm has been measured. Two techniques have been used: a pump-probe approach giving an absolute measurement and a stimulated Raman oscillation threshold technique giving a relative measurement. Both approaches indicate that the Raman gain coefficient is a linear function of pump wavenumber. With the pump polarised along a <111> direction in the crystal, the Raman gain coefficient measured by the pump-probe technique was found to vary from 7.6±0.8 for a pump wavelength of 1280 nm to 78±8 cm/GW for a pump wavelength of 355 nm. With the established dependence of the Raman gain coefficient on the pump wavelength, the Raman gain coefficient can be estimated at any pump wavelength within the spectral range from 355 up to 1450 nm.

Abstract.A comparative study of thermal lensing effect in diode laser pumped N g -and N p -cut Nd:KGd(WO 4 ) 2 (KGW) laser crystals was performed for laser emission polarized along the principle refractive axis, N m . The thermal lens in the N g -cut Nd: KGW was found to be weakly astigmatic with a positive refractive power for both the N m -and N pdirections. For N p -cut Nd:KGW, strong astigmatism was observed and the refractive powers in the N g -and N m -directions had opposing signs. The degree of astigmatism was found to be considerably weaker for the N g -cut Nd:KGW in comparison with the N p -cut one: 0.35 dptr/(W/cm 2 ) and 2.85 dptr/(W/cm 2 ), respectively. The ratio of the thermal lens refractive powers in the planes parallel and perpendicular to the laser emission polarisation were measured as + 1.4 and −0.425 for N g -and N p -cut Nd:KGW respectively.

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Abstract. The anisotropy of thermal lensing and the photo-elastic effect is characterized for diode-pumped Nd:KGd(WO 4 ) 2 crystals cut along the N p and N g optical indicatrix axes and along its optical axis, O = N g +43°, at a laser wavelength of 1067 nm. Distortions in the spatial profile of output laser beam are analyzed. The thermal lens is astigmatic; the orientation of its principal meridional planes, A and B, is determined by the anisotropy of photo-elastic effect. The thermal lens has opposite signs for rays lying in the principal meridional planes for N pand O-cut crystals; and it is positive for an N g -cut crystal. The increase of thermal lens optical power after absorption of 1 W of pump power, i.e. the thermal lens sensitivity factors M A(B) , and astigmatism degree S = |M A -M B | are determined. The photo-elastic effect was found to increase the optical power of thermal lens and was significant for all studied crystal orientations. [5][6][7][8] low-threshold diode-pumped lasers operating in the vicinity of 1 and 1.3 μm. KGW is a biaxial crystal, with three crystal orientations having been employed so far for laser engineering: along the b (N p ) axis [1][2][3][5][6][7][8], along the N g axis [9][10][11][12] and along the optical axis (O) [13,14], i.e. N g +43° in the N p -N g plane [15]. Strong astigmatism of the thermo-optical properties of the material results in significant variation in the sign and value of the thermal lens in crystals cut for light propagation along the N p and N g axes under diode-or flash-lamp pumping [9,12,15,16]. Thermal lens measurements were reported previously for the N p and N g -cut Nd:KGW crystals at the wavelength of 1.06 μm under the flash-lamp-pumping [9,15,16] and at the wavelength of 1.35 μm under the diode -pumping [12]. Keywords