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Neodymium Doped Yttrium Orthvanadate(Nd:YVO4) Crystal

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Nd:YVO4 is one of the most efficient laser host crystal currently existing for diode laser-pumped solid-state lasers. Its large stimulated emission cross-section at lasing wavelength, high absorption coefficient and wide absorption bandwidth at pump wavelength, high laser induced damage threshold as well as good physical, optical and mechanical properties make Nd:YVO4 an excellent crystal for high power, stable and cost-effective diode pumped solid-state lasers. Recent developments have shown that Nd:YVO4 can produce powerful and stable IR, green, bule lasers with the design of Nd:YVO4 and frequency doubling crystals.

Compared with Nd:YAG and Nd:YLF for diode laser pumping, Nd:YVO4 lasers possess the advantages of lower dependency on pump wavelength and temperature control of a diode laser, wide absorption band, higher slope efficiency, lower lasing threshold, linearly polarized emission and single-mode output. For the applications in which more compact design and the single-longitudinal-mode output are needed, Nd:YVO4 shows its particular advantages over other commonly used laser crystals. The diode laser-pumped Nd:YVO4 compact laser and its frequency-doubled green, red or bule laser will be the ideal laser tools of machining, material processing, spectroscopy, wafer inspection, light show, medical diagnostics, laser printing and the most widespread applications.

With advanced technology on growing high optical quality and large size Nd:YVO4 crystals, CASIX steadily provides as large as f35x50 mm3 Nd:YVO4 bulk crystal and f20x20mm3 finished crystal with very low intrinsic optical loss. Now, CASIX massively produces and provides high quality Nd:YVO4 crystals at very competitive prices.


Properties

Main Features:

v Low lasing threshold and high slope efficiency
v Large stimulated emission cross-section at lasing wavelength
v High absorption over a wide pumping wavelength bandwidth
v Optically uniaxial and large birefringence emits polarized laser

1. Basic Properties

Atomic Density: ~1.37x1020 atoms/cm2

Crystal Structure: Zircon Tetragonal, space group D4h, a=b=7.12, c=6.29

Density: 4.22 g/cm2

Mohs Hardness: Glass-like, ~5

Thermal Expansion Coefficient: aa=4.43x10-6/K, ac=11.37x10-6/K

Thermal Conductivity Coefficient: ï êC: 5.23 W/m/K; ^C: 5.10 W/m/K

2. Optical Properties (typically for 1.1 atm% Nd:YVO4, a-cut crystals)

Lasing Wavelengths

914nm, 1064 nm, 1342 nm

Crystal class

positive uniaxial, no=na=nb, ne=nc,
no=1.9573, ne=2.1652, @ 1064nm
no=1.9721, ne=2.1858, @ 808nm
no=2.0210, ne=2.2560, @ 532nm

Sellmeier Equation (for pure YVO4 crystals):
                                  no2=3.77834+0.069736/(l2 - 0.04724) - 0.0108133.l2
                                  ne2=4.59905+0.110534/(l2 - 0.04813) - 0.0122676.l2

Thermal Optical Coefficient:

dna/dT=8.5x10-6/K, dnc/dT=3.0x10-6/K

Stimulated Emission Cross-Section

25.0x10-19 cm2 , @1064 nm

Fluorescent Lifetime

90 ms (about 50  ms for 2 atm% Nd doped) @ 808 nm

Absorption Coefficient

31.4 cm-1 @ 808 nm

Absorption Length

0.32 mm  @ 808 nm

Intrinsic Loss

Less 0.1% cm-1 , @1064 nm

Gain Bandwidth

0.96 nm (257 GHz) @ 1064 nm

Polarized Laser Emission

p polarization; parallel to optic axis (c-axis)

Diode Pumped Optical to Optical Efficiency

> 60%

3. Absorption Curves of Different Doping Nd:YVO4

Nd:YVO4 shows high absorption coefficients at pumping wavelengths. Therefore, a crystal short-in-length (e.g. 1mm) is preferred, and more compact lasers can be constructed by using Nd:YVO4 than using Nd:YAG. Furthermore, it has a wide and smoothly-varied bandwidth of absorption, so that it allows of less stringent requirements of diode laser selection and wavelength control as compared with Nd:YAG. Different doping levels Nd:YVO4 are shown showed as follow

Nd027Curve.JPG (20172 bytes)

Nd30Curve.JPG (22156 bytes)

Absorption Curve of   0.5% doping YVO4
(Thickness:1 mm)
Absorption Curve of   3% doping YVO4
(Thickness:1 mm)

4. Fluorescence Spectra Curve

Ndyvo4curve01.JPG (19309 bytes)

Ndyvo4curve02.JPG (19468 bytes)

(a)

(b)

Normalized fluorescence spectra from 800 nm to 1600 nm of Nd 1.1 at. % doped Nd:YVO4 for p polarization (a) and for s porlarization (b).

5. Laser Properties

               The Nd:YVO4 crystal has large stimulated emission cross-sections (s) at both 1.06 mm and 1.3 mm. The stimulated emission cross-section of an a-axis cut Nd:YVO4 crystal at 1.064mm is about 4 times that of the Nd:YAG crystal. Although the lifetime (t) of Nd:YVO4 is about 2.7 times shorter than that of Nd:YAG, a figure of merit (FOM) for minimum threshold of a-cut Nd:YVO4, which is proportional to the products, is reasonably higher than that of Nd:YAG crystal. Because of its high pump quantum efficiency (hp), the slope efficiency of Nd:YVO4 can be very high if the laser cavity is properly designed. The following Table lists the major laser properties of Nd:YVO4 in comparison with those of Nd:YAG.

Laser properties of Nd:YVO4 crystals vs Nd:YAG

Laser crystal

Nd doped(atm%)

ó
(x10-19cm2)

a
(cm-1)

t
(ms)

la
(mm)

Pth
(mw)

hs
( %)

Nd:YVO4(a-cut)

1.1
2

25

31.2
72.4

90
50

0.32
0.14

78

48.6

Nd:YVO4(c-cut)

1.1

7

9.2

90

231

45.5

Nd:YAG

0.85

6

7.1

230

1.41

115

38.6


APPLICATION

1. Diode Laser-Pumped Nd:YVO4 Lasers

tA threshold of 78 mW and a slope efficiency of 48.5% at 1.064 mm were obtained by using an a-cut 3 mm long Nd:YVO4 crystal with output coupler R = 96%. Under the same conditions, a 5 mm long Nd:YAG crystal has a threshold of 115 mW and a slope efficiency of 38.6%.

tRecently, over 30 W of TEM00 output power was achieved by using a-cut Nd:YVO4 and pumped by 60 W fiber coupled diode lasers. The optical conversion efficiency exceeds 50%. High power and stable infrared output @ 1064 nm and 1342 nm has been available with diode pumped Nd:YVO4 lasers.

tSingle-longitudinal-mode oscillation of a Nd:YVO4 microchip laser has been achieved with high power and high slope efficiency. Such a single mode source has been developed for the use of a master oscillator for injection locking of Nd laser systems.

tBecause of its large stimulated emission cross section at 1.34 mm, Nd:YVO4 is also an efficient laser crystal for diode laser-pumped 1.3 mm laser. By using 1 mm long Nd:YVO4 crystal and pumped by an 850 mW diode laser at 808 nm, 50 mW output at 1.34 mm has been observed, compared to 34 mW from 2 mm long Nd:YAG.

Fig.31.JPG (27411 bytes)

Basic Experimental Scheme of Diode Laser Pumped Nd:YVO4 Green Laser


2. Frequency-doubled Nd:YVO4 Lasers

v    By using the compact design of Nd:YVO4 + KTP crystals, high power green or red light output can be generated in a diode laser pumped Nd:YVO4 laser. When pumped by a 890 mW diode laser, more than 76 mW single mode (TEM00) green output was obtained with a 3x3x1 mm3 Nd:YVO4 and a 3x3x5 mm3 intracavity KTP.

v Diode pumped green lasers has been commercialized with the compact design of Nd:YVO4 + KTP crystals. 2.5 mW green output was achieved in a Nd:YVO4 microchip laser with a very short (9 mm) laser cavity when pumped by a 50 mW diode laser.

v Over 10 W and high stable CW green output @ 532 nm was commerially available with diode pumped Nd:YVO4 and frequency double using NCPM LBO crystals. Sigle longitudinal mode (SLM) green output, Q-switched green and UV outputs were also obtained.

v Over 400 mW blue laser @ 457 nm based on Nd:YVO4+ BBO crystals, is commerical available .


Standard Specs and Note

Standard Specs. of CASIX's Nd:YVO4 Crystals

Nd: Dopant Level

0.1 - 3.0 atm%

Standard Dimensions

3x3x3 mm3, 3x3x1 mm3, 3x3x0.5 mm3

Wavefront Distortion

< l/8 at 633 nm

Scattering Sites

invisible, probed with a He-Ne laser

Orientation

0.5 deg

Dimensional Tolerance

+0.1/-0.1 mm

End-faces Configuration

Plano/Plano

Surface quality

10/5 Scratch/Dig per MIL-O-13830B

Flatness

l/10 at 633 nm

Clear Aperture

> Central 90%

Parallelism

< 10 arc sec.

Intrinsic Loss

< 0.1% cm-1


Note

1. Other specifications of Nd:YVO4 crystals and coatings are available upon request.

2. Tm:YVO4 crystal for eyesafe and medical lasers @ 1940 nm, Er:YVO4, Yb:YVO4 and other ion doped YVO4 crystals are also grown by CASIX.

CASIX provides the complete diode pumped laser kits, including laser crystals (Nd:YVO4 and Nd:YAG), NLO crystals (KTP, or LBO and BBO) and laser optics. Please refer to page 62 for information about diode pumped laser optics kits.


Copyright  1998 CASIX, Inc. All rights reserved. Last Revised: May 19, 1999
Web Page maintained by : Contact@CASIX.com

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