A. A. Pavlyuk

Orthorhombic ferroelectric and ferroelastic Gd2(MoO4)3 crystal — a new many-purposed nonlinear and optical material: efficient multiple stimulated Raman scattering and CW and tunable second harmonic generation

Abstract The nonlinear optical properties of a ferroelectric and ferroelastic β′-Gd2(MoO4)3 laser crystal-host were studied by second harmonic generation (SHG) and stimulated Raman scattering (SRS) experiments using different laser sources for excitation. It is shown that the investigated crystals are very attractive for SHG with IR CW lasers as well as for continuously tunable SHG under illumination with a femtosecond hyper-continuum light source. Furthermore, up to five Stokes and five anti-Stokes lines have been obtained in picosecond SRS experiments with a total conversion efficiency of about 70%. Interaction of SHG and SRS, as well as a new effect, which may be called quasi-hyper SRS, have been observed with insulating crystal for the first time. We classify the β′-Gd2(MoO4)3:Nd as a promising laser medium for pulsed and CW self-frequency doubling lasers.

Optical and nonlinear laser properties of the χ(3)-active monoclinic α-KY(WO4)2 crystals

Monoclinic α-KRE(WO4)2 crystals are grown. Their structure is described in two crystallographic settings. The principal refractive indices are determined and the coefficients and characteristic wavelengths are used for calculating refractive indices by the Selmeyer formulas. The data on the anisotropic parametric Raman generation in these crystals under the picosecond pumping are discussed.

Thermal lens study in diode pumped N-g- and N-p-cut Nd:KGd(WO4)(2) laser crystals

A comparative study of thermal lensing effect in diode laser pumped Ng- and Np-cut Nd:KGd(WO4)2 (KGW) laser crystals was performed for laser emission polarized along the principle refractive axis, Nm. The thermal lens in the Ng-cut Nd: KGW was found to be weakly astigmatic with a positive refractive power for both the Nm- and Np-directions. For Np -cut Nd:KGW, strong astigmatism was observed and the refractive powers in the Ng- and Nm-directions had opposing signs. The degree of astigmatism was found to be considerably weaker for the Ng-cut Nd:KGW in comparison with the Np-cut one: 0.35 dptr/(W/cm2) and 2.85 dptr/(W/cm2), 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 Ng- and Np-cut Nd:KGW respectively.

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

We measured the thermo-optic coefficients dn/dT of anisotropic Nd:KGd(WO(4))(2) crystals at the wavelengths of 1.064 μm and 532 nm (300 K) by a beam deflection method. The values of dn/dT are determined to be dn(p)/dT = -16.0 × 10(-6) K(-1), dn(m)/dT = -11.8 × 10(-6) K(-1), and dn(g)/dT = -19.5 × 10(-6) K(-1) (at 1.064 μm) and dn(p)/dT = -14.3 × 10(-6) K(-1), dn(m)/dT = -10.0 × 10(-6) K(-1), and dn(g)/dT = -15.0 × 10(-6) K(-1) (at 532 nm). Thermal lensing in the flashlamp-pumped N(p)- and N(g)-cut Nd:KGd(WO(4))(2) laser rods was studied at 1.064 μm by a probe beam technique in the nonlasing conditions, and the contribution of the photoelastic term to the thermal lens optical power was estimated. Athermal propagation directions with the definitions dn/dT + (n-1)α(T) = 0 and dn/dT + nα(T) = 0 were found in Nd:KGd(WO(4))(2).

Anisotropy of the photo-elastic effect in Nd:KGd(WO4)2 laser crystals

The anisotropy of thermal lensing and the photo-elastic effect is characterized for diode-pumped Nd : KGd(WO4)2 crystals cut along the Np and Ng optical indicatrix axes and along its optical axis, O = Ng + 43°, at a laser wavelength of 1067 nm. Distortions in the spatial profile of the 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 Np- and O-cut crystals; it is positive for an Ng-cut crystal. The increase of thermal lens optical power after absorption of 1 W of pump power, i.e. the thermal lens sensitivity factors MA(B), and astigmatism degree S = |MA–MB| are determined. The photo-elastic effect was found to increase the optical power of the thermal lens and was significant for all studied crystal orientations.

High‐order stimulated Raman scattering combined with second harmonic generation in [χ(2)+χ(3)]‐nonlinear LaBGeO5, β′‐Gd2(MoO4)3 and Ca4Gd(BO3)3O laser host crystals under picosecond excitation

New frequency conversion processes leading to emission in the visible spectral range were observed for the first time by multiple Stokes and anti-Stokes Raman generation arising from intrinsic second harmonic generation in three different [χ(2)+χ(3)]-nonlinear LaBGeO5, β′-Gd2(MoO4)3 and Ca4Gd(BO3)3O laser host crystals under picosecond pumping at a fundamental wavelength of 1 μm.

High-power, efficient, semiconductor saturable absorber mode-locked Yb:KGW bulk laser.

A high-power, diode-pumped, semiconductor saturable absorber mode-locked Yb(5%):KGW bulk laser was demonstrated with high optical-to-optical efficiency. Average output power as high as 8.8 W with optical-to-optical efficiency of 37.5% was obtained for Nm-polarized laser output with 162 fs pulse duration and 142 nJ pulse energy at a pulse repetition frequency of 62 MHz. For Np polarization, 143 fs pulses with pulse energy of 139 nJ and average output power of up to 8.6 W with optical-to-optical efficiency of 31% were generated.

Highly efficient 12 W diode-pumped actively Q-switched Yb:KGd(WO 4 ) 2 laser

A compact diode-pumped actively Q-switched Yb:KGW laser is demonstrated with an optical-to-optical efficiency of 50%. In a 3-mirror laser cavity configuration output power of 12.2 W with repetition rate up to 50 kHz and pulse duration of 10-24 ns was obtained. The maximum pulse peak power of 70 kW was achieved. The laser output beam profile was Gaussian up to maximum pump powers with M2 factor less than 1.2.

Thermal lensing in Nm-cut monoclinic Tm:KLu(WO4)2 laser crystal

The thermal lensing effect is characterized in slab-shaped monoclinic Tm:KLu(WO4)2 crystal cut for light propagation along the Nm optical indicatrix axis (the light polarization is E???Np). The optical power of the thermal lens was measured directly by a modified probe beam technique. Alternatively, it was calculated on the basis of measured material parameters, including the thermal expansion coefficients along the optical indicatrix axes (?p?=?3.1, ?m?=?11.1 and ?g?=?13.1(10?6?K?1)) and the principal thermo-optic coefficients (dnp/dT?=??13.3, dnm/dT?=??5.9, dng/dT?=??9.0(10?6?K?1) at 1.95??m). The two methods are in good agreement and confirm the defocusing action of the thermal lens; the ?effective? thermo-optic coefficient ? for Nm-cut crystal is ?2.1???0.5???10?6?K?1. The fractional head load ?h for slab-shaped Tm:KLu(WO4)2 crystal is 0.33???0.03 (as determined from ISO-standard laser calorimetry).

Thermo-optic coefficients study in KGd(WO4)2 and KY(WO4)2 by a modified minimum deviation method.

Thermo-optic coefficients anisotropy was characterized in monoclinic potassium (rare-earth) double tungstates KGd(WO4)2 and KY(WO4)2 in the spectral range of 0.44-0.63 μm by a modified minimum deviation method. This approach takes into account the changes in the shape and dimensions of the prismatic sample caused by the anisotropic thermal expansion effect under uniform heating together with the conventional measurements of minimum deviation angle. At room temperature at the wavelength of 633 nm, principal refractive indices for KGdW are n(p)=2.0135, n(m)=2.0458, and n(g)=2.0860, and for KYW they are n(p)=1.9979, n(m)=2.0396, and n(g)=2.0869. Optical axes position for KGdW (KYW) crystals is N(g) ± 42.60 (N(g) ± 44.1°) in the N(p)-N(g) plane. For both crystals, all the thermo-optic coefficients are negative and equal dn(p)/dT=-10.6, dn(m)/dT=-8.4, and dn(g)/dT=-15.2 for KGdW, and dn(p)/dT=-10.1, dn(m)/dT=-7.3, and dn(g)/dT=-8.4 for KYW [10(-6) K(-1)] (at 633 nm).