Nd:YVO4 (neodymium-doped yttrium vanadate) crystal is a laser host crystal with excellent performance, suitable for making all-solid-state lasers pumped by laser diodes (LD). The crystal has the following characteristics: low laser threshold, high slope efficiency, large stimulated emission cross section, great absorption of pump light in a wide wavelength range, and single-mode tuning, high resistance to light damage. The latest progress shows that the combination of Nd:YVO4 crystal and KTP crystal can be used to make high-power stable infrared, green or red lasers.

The Nd:YVO4 crystal belongs to the tetragonal system and is a positive uniaxial crystal. Nd:YVO4 crystal has been widely recognized as a very important laser material since its inception in 1966. However, the researchers found that such crystals have defects such as scattering centers and absorption color centers, making it impossible to grow high-quality crystals of sizes suitable for flashlamp pumping. Fortunately, it has great absorption and gain to the diode radiation wavelength, large emission cross-section, and good polarization characteristics of the output laser, which are enough to mask the shortcomings of its small growth size. Nd:YVO4 crystal is a laser crystal material with excellent performance that is very suitable for laser diode pumping.

Some of its characteristic parameters are given below:
Absorption wavelength (nm): 808.5;

Absorption coefficient (cm-1): 31.4 (π polarization, 808nm);
Emission wavelength (nm): 1064.3;

Emission cross section (cm2): 25×10-19 (1064nm);
Fluorescence lifetime (μs): 94 (1.22at.%);

Refractive index (@1064nm): no=1.957, ne=2.165;
Thermal light coefficient (/K, @300K): dno/dT=8.5×10-6, dne/dT=3.0×10-6

Since this crystal is naturally birefringent, its absorption of the pump light is polarization dependent. If the polarization direction of the pump light is consistent with the laser radiation direction, the absorption of the pump light is the strongest. Figure 1(a) is the absorption spectrum of Nd:YVO4 crystal. It can be seen that the crystals exist between 800 and 900 nm

Two absorption peaks: 808.5nm and 879.8nm, respectively. On the other hand, the absorption coefficient of the crystal is larger for π-polarized pump light than for σ-polarized pump light, and the absorption coefficient of Nd:YVO4 in the π direction is about 4 times that of Nd:YAG. Therefore, in order to make full use of the energy of the pump light, π-polarized pumping is usually used.

Nd:YVO4 crystal not only has strong polarization absorption characteristics, but also has strong polarization radiation characteristics. The laser output is linearly polarized along the π or σ direction, so that unnecessary thermal birefringence in the crystal can be avoided, which is also the biggest feature that distinguishes them from Nd:YAG crystals. Figure 4-1b shows the emission spectrum of the crystal. It can be seen that its polarized emission along the π direction is strong, and the emission cross section of Nd:YVO4 is larger, which leads to the following results in practical applications: The average output power obtained by Nd:YVO4 is larger, and the light-to-light conversion efficiency is higher. high.

In conclusion, Nd:YVO4 has the advantages of larger absorption coefficient, higher emission cross-section, polarization absorption and emission characteristics, larger absorption bandwidth, and insensitivity to the temperature change of the diode compared with the conventional Nd:YAG crystal. Therefore, it is widely used in LD-pumped all-solid-state lasers. However, due to its large emission cross section and short upper energy level lifetime, the energy storage capacity of Nd:YVO4 is far inferior to that of Nd:YAG, which is not conducive to the output of Q-switched pulses with high energy and high peak power. The advantages are only limited to the continuous wave output of high average power and high conversion efficiency. In addition, the thermal conductivity of Nd:YVO4 is very small, only half of that of Nd:YAG, so it is not conducive to the realization of high-power continuous wave output.