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Vanadate Lasers

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Definition: lasers based on rare-earth-doped yttrium, gadolinium or lutetium vanadate crystals, usually Nd:YVO4

German: Vanadat-Laser

Categories: lasers, optical materials

How to cite the article; suggest additional literature

The term vanadate laser is usually used for lasers based on neodymium-doped vanadate crystals. In particular, these include yttrium vanadate (Nd:YVO4), gadolinium vanadate (Nd:GdVO4), and lutetium vanadate (Nd:LuVO4). These vanadates are also called orthovanadates. Such materials have been known for a long time [1], but became popular only many years later, because for a long period it was difficult to grow them with high optical quality in sufficiently large size. Apart from progress in crystal growth, the advent of diode pumping increased the interest in vanadates also because smaller crystals could be used.

There are also vanadate crystals doped with other rare earth ions, e.g. with ytterbium, erbium, thulium or holmium doping. Due to the similar size, yttrium, gadolinium or lutetium ions can be replaced with laser-active rare earth ions without strongly affecting the lattice structure. This is important e.g. for preserving high thermal conductivity of the doped materials.

Vanadate crystals are naturally birefringent, which eliminates thermally induced depolarization loss in high-power lasers. Also, the laser gain is strongly polarization dependent (→ polarization of laser emission); the highest gain is usually achieved for polarization along the c axis. The pump absorption is also strongly polarization-dependent (except at special wavelengths), which can cause problems e.g. when using a fiber-coupled pump source with drifting polarization.

For Nd:YVO4, the typical laser emission wavelength is 1064 nm, i.e., the same as for Nd:YAG. Other important emission wavelengths are 914 and 1342 nm. The latter emission line is much stronger than the corresponding 1.32-μm line in Nd:YAG, thus allowing for much better performance in 1.3-μm operation.

Table 1: Some properties of Nd:YVO4 = neodymium-doped yttrium vanadate.

PropertyValue
chemical formulaNd3+:YVO4
crystal structuretetragonal
mass density4.22 g/cm3
Moh hardness5–6
Young's modulus133 GPa
tensile strength53 MPa
melting point1810 °C
thermal conductivity≈ 5 W / (m K)
(values around 9–12 are also found in the literature)
thermal expansion coefficient11 × 10−6 K−1 (c direction), 4.4 × 10−6 K−1 (a direction)
transparency range0.3–2.5 μm
birefringencepositive uniaxial
refractive index at 1064 nm2.17 for c polarization (extraordinary),
1.96 ordinary index
temperature dependence of refractive index3 × 10−6 K−1 in c direction, 8.5 × 10−6 K−1 in the a direction
Nd density for 1% at. doping1.24 × 1020 cm−3
fluorescence lifetime90 μs
absorption cross section at 808 nm60 × 10−20 cm2 (c polarization)
emission cross section at 1064 nm114 × 10−20 cm2 (c polarization)
gain bandwidth1 nm

Nd:YVO4 lasers are usually diode-pumped, but can also be lamp-pumped. Compared with Nd:YAG (→ YAG lasers), Nd:YVO4 exhibits a much higher pump absorption and gain (due to the very high absorption and laser cross sections), a broader gain bandwidth (around 1 nm), a much broader wavelength range for pumping (often eliminating the need to stabilize the pump wavelength), a shorter upper-state lifetime (≈ 100 μs for not too high neodymium concentrations), a higher refractive index, a lower thermal conductivity, and birefringence. The consequences of these differences for various modes of laser operation are the following:

Compared with Nd:YVO4, Nd:GdVO4 has a similar thermal conductivity, a slightly shorter emission wavelength (1063 nm), a somewhat larger gain bandwidth, lower emission cross sections, and still higher pump absorption. Note, however, that the published data concerning thermal conductivity of vanadate crystals differ considerably, so there are some significant uncertainties.

Bibliography

[1]J. R. O'Connor, “Unusual crystal-field energy levels and efficient laser properties of YVO4:Nd”, Appl. Phys. Lett. 9, 407 (1966)
 [2]A. I. Zagumennyi et al., “The Nd3+:GdVO4 crystal: a new material for diode-pumped lasers”, Sov. J. Quantum Electron. 22, 1071 (1992)
[3]J. L. Blows et al., “Heat generation in Nd:YVO4 with and without laser action”, IEEE Photon. Technol. Lett. 10 (12), 1727 (1998)
[4]N. Hodgson et al., “High power TEM00 mode operation of diode-pumped solid-state lasers”, Proc. SPIE 3611, 119 (1999)
[5]Y. Sato and T. Taira, “The studies of thermal conductivity in GdVO4, YVO4, and Y3Al5O12 measured by quasi-onedimensional flash method”, Opt. Express 14 (22), 10528 (2006)
[6]N. Pavel et al., “In-band pumping of Nd-vanadate thin-disk lasers”, Appl. Phys. B 91 (3-4), 415 (2008)
[7]J. Liu et al., “Comparative study of high-power continuous-wave laser performance of Yb-doped vanadate crystals”, IEEE J. Quantum Electron. 45 (7), 807 (2009)
[8]Y. Yan et al., “Near-diffraction-limited, 35.4 W laser-diode end-pumped Nd:YVO4 slab laser operating at 1342 nm”, Opt. Lett. 34 (14), 2105 (2009)
[9]D. Sangla et al., “Highly efficient Nd:YVO4 laser by direct in-band diode pumping at 914 nm”, Opt. Lett. 34 (14), 2159 (2009)
 [10]G. Turri et al., “Temperature-dependent stimulated emission cross section in Nd3+:YVO4 crystals”, J. Opt. Soc. Am. B 26 (11), 2084 (2009)
[11]X. Délen et al., “Temperature dependence of the emission cross section of Nd:YVO4 around 1064 nm and consequences on laser operation”, J. Opt. Soc. Am. B 28 (5), 972 (2011)

(Suggest additional literature!)

See also: laser crystals, YAG lasers, YLF lasers, neodymium-doped gain media, rare-earth-doped gain media, mode-locked lasers, Spotlight article 2006-09-16, Spotlight article 2006-11-04
and other articles in the categories lasers, optical materials


Dr. R. Paschotta

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