Thermo-optic coefficients and thermal lensing in Nd-doped KGd(WO4)2 laser crystals

Analysis of a thermal lens in a diamond Raman laser operating at 1.1 kW output power

We report experimental observations of thermal lens effects in a diamond Raman laser operating up to 1.1 kW output power in a quasi- steady-state regime. Measured changes in the output beam parameters as a function of output power, including beam quality factor and beam divergence after a fixed focusing lens, are compared to modelling enabling us to track the development of a thermal lens up to 16 diopters at maximum output power. Analysis shows that good agreement between model and experiment is obtained by considering the power deposition profile and the spatial overlap with the laser mode. The results clarify previous work that raised questions about thermal lens effects in the diamond gain medium and provides increased confidence in thermal models for determining the power limits for the current design.

Multiwatt continuous wave Nd:KGW laser with hot-band diode pumping

We have demonstrated what we believe is the first continuous wave neodymium-doped potassium gadolinium tungstate crystal (Nd:KGW) laser with hot-band diode pumping at ∼910  nm. This pumping wavelength reduced the quantum defect by >46% as compared to conventional ∼810  nm pumping and resulted in significantly lower thermal lensing. The laser produced 2.9 W of average output power at 1067 nm in a diffraction-limited beam for an absorbed pump power of 8.3 W. The slope efficiency and optical-to-optical efficiency were found to be 43% and 35%, respectively. Significant reduction of quantum defect offered by this pumping wavelength and availability of suitable high-power laser diodes opens up an attractive way to further power and efficiency scaling of Nd:KGW lasers.

Dispersion and anisotropy of thermo-optic coefficients in tetragonal GdVO(4) and YVO(4) laser host crystals: erratum

We addressed errors found in our measurements of thermo-optic coefficients and thermal coefficients of the optical path (TCOP) in tetragonal vanadates, YVO(4) and GdVO(4) [Appl. Opt.52, 698 (2013)]. Modified thermo-optic dispersion formulas are presented for these laser host crystals.

Athermal directions in KGd(WO4)2 and KLu(WO4)2 crystals under uniform heating

Athermal (AT) propagation directions in KGd(WO4)2 and KLu(WO4)2 crystals are found for two configurations (monolithic and laser cavity) at two wavelengths of 633 and 1064 nm. Four branches of solutions for AT directions exist for both configurations in KGd(WO4)2 and for the laser cavity configuration in KLu(WO4)2; for the monolithic configuration there are one or two branches for wavelengths of 633 and 1064 nm, respectively. Two of the branches for the laser cavity configuration pass in the vicinity of the crystal optical axis, where solutions are extremely sensitive to the direction of propagation. In some cases discrepancy in thermo-optic and thermal expansion parameters found by different authors may lead to the appearance (or disappearance) of AT directions.

Dispersion and anisotropy of thermo-optic coefficients in tetragonal GdVO4 and YVO4 laser host crystals

A detailed experimental study of dispersion and anisotropy of thermo-optic coefficients dn/dT and thermal coefficients of the optical path W=dn/dT+(n-1)α is performed for tetragonal YVO(4) and GdVO(4) laser host crystals by a laser beam deviation method. It is supported by theoretical description of thermo-optic effects, taking into account the volumetric thermal expansion effect and the temperature dependence of electronic bandgap E(g). Linear thermal expansion coefficients α were also determined by a dilatometric technique. Thermo-optic dispersion formulas describing temperature variation of the refractive index and the thermal lens effect are derived for a wide spectral range of 0.4-2 μm. It allows us to estimate the values of E(g) and dE(g)/dT for the studied crystals. The influence of materials parameters and pumping conditions on thermal lens properties is discussed, revealing the significant impact of anisotropic and temperature-dependent thermal conductivity.