|Neodymium-doped yttrium-vanadate crystals (Nd:YVO4) are some of the most effective laser crystals for coherent sources with diode pumping, especially for sources with low and middle power density. Their absorption and emission properties are even better than those of Nd:YAG crystals.|
A laser diode pumped Nd:YVO4 crystal was combined with crystals with a high non-linearity factor (LBO, BBO or KTP) to shift the frequency of the lasing output from the near-IR to the green, blue or even UV spectral region. This combination in solid-state lasers is an ideal tool for most common laser applications, including material processing, spectroscopy, wafer quality control systems, laser printing, etc. It is proven that diode-pumped ND: YVO4 solid-state lasers quickly gain markets where water-cooled ion lasers and lamp-pumped lasers traditionally dominate, especially when a compact design and emission with a single longitudinal mode are required.
Advantages of Nd:YVO4 lasers over Nd:YAG:
– The absorption coefficient is 5 times greater in the whole wide pumping range around 808 nm (besides, the dependence on the pump wavelength is much lower, and there is also a strong tendency to form single-mode emission);
– The stimulated emission cross-section is 3 times larger at a wavelength of 1064 nm;
– Lower generation threshold and higher differential quantum efficiency;
– Uniaxial crystal with double refraction: linearly polarized radiation.
– Doping: 0.1% – 3%;
– Doping material concentration tolerance: ±0.05% (atoms%<1%), ±0.1% (atoms%≥1%);
– Crystals of various sizes and of high quality;
– 10 000 items Nd:YVO4 per month 3x3x0.5 – 4x4x8 mm3 in size;
– Competing prices.
Nd:YVO4 crystal absorption curve ( 0.5% doping, 4 mm thick)
Nd:YVO4 crystal properties
|Parameters||Description and values|
|Atoms concentration||1.26×1020 atoms/cm3 (Nd 1.0%)|
Unit cell parameter
|Zircon Tetragonal, space group D4h-I4/amd|
|Mineralogical hardness||4-5 (glass)|
|Thermal expansion coefficient (300 K)||αa=4.43×10-6/K|
|Thermal conductivity coefficient (300 K)||∥C：0.0523 W/cm/К|
|Laser wavelength||1064 nm, 1342 nm|
|Thermo-optic coefficients (300 K)||dno/dT=8.5×10-6/K|
|Stimulated emission cross-section||25×10-19 cm2 at 1064 nm|
|Fluorescence lifetime||90 ms (1%)|
|Absorption coefficient||31.4 cm-1 at 810 nm|
|Inner losses||0.02 cm-1 at 1064 nm|
|Amplification bandwidth||0.96 nm at 1064 nm|
|Polarized laser radiation||Polarized; Parallel to the optic axis (c-axis)|
|Pump efficiency as to laser optical efficiency||>60%|
|Selmeyer’s equation (λ in um)||no2=3.77834+0.069736/(λ2-0.04724)-0.010813λ2|
Nd:YVO4 lasers properties
1. One of the most appealing properties of Nd:YVO4 crystals is their absorption coefficient, which is 5 times bigger than that of Nd:YAG crystals in a wide range with the peak around 808 nm, what corresponds to the standard wavelength of laser diodes of high power. It means that it is possible to use more compact crystals in lasers, resulting in size reduction of a coherent radiation source system as a whole. Besides, a lower power of a pumping laser diode is needed, which, in its turn, increases the laser diode lifetime. The absorption bandwidth of Nd:YVO4 may be 2.4 – 6.3 times bigger than that of Nd:YAG crystals. High efficiency of pumping allows choosing less expensive laser diodes for pumping.
2. Nd:YVO4 crystals have a wider cross-section of stimulated emission at both 1064 nm and 1342 nm wavelengths. At 1064 nm wavelength lasing, this cross-section is 4 times as big as the cross-section of a similar Nd:YAG crystal; at 1340 nm lasing the cross-section is 18 times bigger. This enables Nd:YVO4 lasers to support powerful single mode radiation at both wavelengths.
3. Unlike Nd:YAG crystals with cubic symmetry, Nd:YVO4 crystals are single uniaxial, that makes it possible to generate linear polarized emission. Though, the service lifetime of Nd:YVO4 is 2.7 times shorter than that of Nd:YAG, their differential quantum efficiency is rather high due to the high pumping efficiency.
Comparison of Nd:YVO4 and Nd:YAG characteristics is given below:
stimulated emission cross-section (σ), absorption coefficient (α), fluorescence lifetime (τ), absorption length (Lα), threshold power (Pth) and quantum efficiency of pumping (ηs).
Nd:YVO4 and Nd:YAG characteristics
Comparison of Nd:YVO4 and diode-doped Nd:YAG lasers
|Crystal||Size (mm3)||Pumping power||Output emission (at 1064 nm)|
|Nd:YVO4||3×3×1||850 mW||350 mW|
|Nd:YVO4||3×3×5||15 W||6 W|
|Nd:YAG||3×3×2||850 mW||34 mW|
Diode-pumped Nd:YVO4+KTP laser
– 8 W green light generated by an Nd:YVO4 (0.5% doping, 15 W pumping laser diode. KTP crystal inside the resonator.
– 200 mW green light generated by an Nd:YVO4 (2% doping, 1 W pumping laser diode.
– KTP crystal: 2x2x5 mm3, Nd:YVO4 crystal: 3x3x1 mm3.
– Both butt-ends with anti-reflective coating for 1064/808 nm, R<0.2% at 1064 nm, R<2% at 808 nm;
– 1 surface: high reflective coefficient coating at 1064&532 nm, with high transmittance coefficient for 808 nm, R>99.8% at 1064&532, T>90% at 808 nm;
– 2 surface: anti-reflective coating at 1064&532 nm, R<0.2% at 1064 nm; R<0.5% at 532 nm;
– 1 surface: high reflective coefficient coating at 1064 nm, with high transmittance coefficient for 808 nm, R>99.8% at 1064, T>95% at 808 nm;
– 2 surface: anti-reflective coating at 1064 nm, R<0.1% at 1064 nm;
– 1, 2 surface: anti-reflective coating, 3 surface: gilding / chrome plating;
– Both butt-ends with anti-reflective coating at 1064 nm, 3 surface anti-reflection coating for 808 nm;
– Other variants of coating at request.