Nd:YVO4

Neodymium-doped yttrium orthovanadate (Nd:YVO₄) is a crystalline material formed by adding neodymium ions to yttrium orthovanadate. It is commonly used as an active laser medium for diode-pumped solid-state lasers. It comes as a transparent blue-tinted material. It is birefringent, therefore rods made of it are usually rectangular. 

Properties of Nd:YVO4/YVO4 Crystal

Neodymium Doped Yttrium Orthvanadate (Nd:YVO4) is one of the most efficient laserhost 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 purrip wavelcngth, high lnscr induced darraye threshold as well as good physical9 optical and mechanical properties make Nd:YVO4 an excellent crysta for the high power, stable and cost-effective diode lasenpumped solid-state tasers. Recent developments have shown that Nd:YVO4 micro-lasers can produce powerful and stable IR and green or red lasers with the design of Nd:YVO4 + KTP.

Optical Properties:

Lasing Wavelength :	1064nm, 1342nm
Refractive Indices:	@1064nm	1.9573(no)	2.1652(ne)
	@808nm	1.9721(no)	2.1858(ne)
	@532nm	2.0210(no)	2.2560(ne)
Sellmeier Equations: (Pure YVO4,l in µm)	no2 = 3.77834 + 0.069736 / (l2 - 0.04724) - 0.0108133l2
	ne2 = 4.59905 + 0.110534 / (l2 - 0.04813) - 0.0122676l2
Therm-OpticCoefficient:(10-6/K)	dna/dT=8.5	dnb/dT=8.5	dnc/dT=3.0
Absorption Coefficient:	~31.4%/cm @808nm
Absorption Length:	0.32mm @808nm
Stimulated Emission Cross-Section:	2.50x10-18 cm2 @1064nm
Fluorescent Lifetime:	90 µs (about 50 µs for 2 atm% Nd doped) @ 808nm
Intrinsic Loss:	0.02/cm @ 1064nm
Gain Bandwith:	0.96nm (257 GHz) @ 1064nm
Polarized Laser Emission:	ppolarization;parallel to optic axis (c-axis)
Diode Pumped Optical to Optical Efficiency:	>60%

Physical Properties:

Crystal Structure:	Zircon Tetragonal, space group D4h
Cell Parameters:	a=b=7.12Å, c=6.29Å
Mohs Hardness:	»5
Density:	4.22g/cm3
Hygroscopic Susceptibility	no
Thermal Conductivity(W/cm·K):	parallel to c: 0.0523; vertical to c: 0.0510
Thermal Expansion Coefficient:	parallel to a: 4.43x10-6; parallel to c: 11.37x10-6

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Cr:YAG

Chromium (IV)-doped YAG (Cr:YAG) provides a large absorption cross section in the 0.9-1.2 micrometer spectral region, which makes it an attractive choice as a passive Q-switch for Nd-doped lasers. The resulting devices are solid-state, compact and low-cost. Cr:YAG has high damage threshold, good thermal conductivity, good chemical stability, resists ultraviolet radiation, and is easily machinable. It is replacing more traditional Q-switching materials like lithium fluoride and organic dyes. The dopant levels used range between 0.5 and 3 percent (molar). Cr:YAG can be used for passive Q-switching of lasers that operate at wavelengths between 1000 and 1200 nm, such as those based on Nd:YAG, Nd:YLF, Nd:YVO₄, and Yb:YAG.

Cr:YAG can be also used as a laser gain medium itself, producing tunable lasers with outputs adjustable between 1350 and 1550 nm. The Cr:YAG laser can generate ultrashort pulses (in the femtoseconds range) when it is pumped at 1064 nm by a Nd:YAG laser.

Nd:YAG

Neodymium-doped YAG (Nd:YAG) was developed in the early 1960s, and the first working Nd:YAG laser was invented in 1964. Neodymium-YAG is the most widely used active laser medium in solid-state lasers, being used for everything from low-power continuous-wave lasers to high-power Q-switched(pulsed) lasers with power levels measured in the kilowatts. The thermal conductivity of Nd:YAG is higher and its fluorescence lifetime is about twice as long as that of Nd:YVO₄ crystals, however it is not as efficient and is less stable, requiring more precisely controlled temperatures. The best absorption band of Nd:YAG for pumping the laser is centered at 807.5 nm, and is 1 nm wide.

Vacuum Coating

The product passes through the portion of the coater known as the application chamber at a constant speed of up to 500' per minute (15m/min). As it enters the chamber, it passes through a template which has the same shape hole, or profile, in itself to the shape of the product passing through. As it exits the chamber, it passes through another template called the exit template that also has a similar matching profile.

Chemical Vapor Deposition

Chemical vapor deposition (CVD) is a chemical process used to produce high-purity, high-performance solid materials. The process is often used in the semiconductor industry to produce thin films. In typical CVD, the wafer (substrate) is exposed to one or more volatile precursors, which react and/ordecompose on the substrate surface to produce the desired deposit. Frequently, volatile by-products are also produced, which are removed by gas flow through the reaction chamber.

CVD is practiced in a variety of formats. These processes generally differ in the means by which chemical reactions are initiated.

• Classified by operating pressure:
  • Atmospheric pressure CVD (APCVD) – CVD at atmospheric pressure.
  • Low-pressure CVD (LPCVD) – CVD at sub-atmospheric pressures.^[1] Reduced pressures tend to reduce unwanted gas-phase reactions and improve film uniformity across the wafer.
  • Ultrahigh vacuum CVD (UHVCVD) – CVD at very low pressure, typically below 10⁻⁶ Pa (~10⁻⁸ torr). Note that in other fields, a lower division between high and ultra-high vacuum is common, often 10⁻⁷ Pa.

Most modern CVD is either LPCVD or UHVCVD.

• Classified by physical characteristics of vapor:
  • Aerosol assisted CVD (AACVD) – CVD in which the precursors are transported to the substrate by means of a liquid/gas aerosol, which can be generated ultrasonically. This technique is suitable for use with non-volatile precursors.
  • Direct liquid injection CVD (DLICVD) – CVD in which the precursors are in liquid form (liquid or solid dissolved in a convenient solvent). Liquid solutions are injected in a vaporization chamber towards injectors (typically car injectors). The precursor vapors are then transported to the substrate as in classical CVD. This technique is suitable for use on liquid or solid precursors. High growth rates can be reached using this technique.
• Plasma methods (see also Plasma processing):
  • Microwave plasma-assisted CVD (MPCVD)
  • Plasma-Enhanced CVD (PECVD) – CVD that utilizes plasma to enhance chemical reaction rates of the precursors.^[2] PECVD processing allows deposition at lower temperatures, which is often critical in the manufacture of semiconductors. The lower temperatures also allow for the deposition of organic coatings, such as plasma polymers, that have been used for nanoparticle surface functionalization.^[3]
  • Remote plasma-enhanced CVD (RPECVD) – Similar to PECVD except that the wafer substrate is not directly in the plasma discharge region. Removing the wafer from the plasma region allows processing temperatures down to room temperature.