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Ruby Laser Rods

Demonstrated over 30 years ago, Ruby continues to be a primary selection to provide intense, high power pulses of visible spectrum energy. Ruby Laser

Roditi supplies Czochralski grown Ruby in a wide range of sizes, with consistent optical quality which makes predictable system performance possible. Ruby laser material combines excellent physical and optical properties with good laser performance characteristics. The thermal conductivity of the aluminium oxide host is superior to all other solid state laser host. It is very hard, chemically inert, and can be fabricated and polished to demanding specifications.

Commercial lamps effectively pump Ruby's broad absorption bands to produce a 694.3 nm output, characterised by a long fluorescent lifetime and large energy storage and gain.

Specific system performance characteristics are dependent upon cavity design and efficiency, end reflectors. pump source, cooling techniques, cavity length, rod dopant level, and a number of other related and interactive properties of the system.

The optical quality of Ruby Laser Crystal is paramount. It is necessary to produce crystals that are free of measurable defects which affect the refractive index.

Large diameter crystals are grown which provide clear radial zones of over 25.4 mm diameter, adequate for all rod requirements. Radial chromium distribution and crystal structure are tightly controlled. Optical windows are cut from each crystal and evaluated for absorption to verify chromium levels.

Every rod is tested interferometrically for optical quality to consistently provide laser rods that produce the best beam quality.

Rod Selection

Ruby is available in two discrete chromium dopant levels, 0.03% and 0.05% by weight substitution of Cr_2O3 for Al_2O3. However, the most often selected is 0.05%.

Laser operating at or near threshold power take advantage of the lower threshold and better slope efficiency of the 0.03% material in this narrow region.

Cases where full and uniform pumping of large diameter amplifiers is desired to avoid degradation of high quality beans that might result from the use of greater doping levels.

Applications

High - power Q - switched systems, capable of creating the energy densities needed to generate Thomson scattering in plasma diagnostics.
High - brightness holographic camera systems with long coherent length.
High - power systems useful for frequency doubling into the UV spectrum.
Laser metal working systems capable of drilling holes in hard materials.
Medical laser systems used for cosmetic dermatology and tattoo removal.

Physical and Optical Properties

Density		3.98 g/cc		Refractive index at 700 nm	1.7638 Ordinary Ray
Melting Point		2040° C			1.7556 Extraordinary Ray
Young's Modulus		345 Gpa		Birefringence	0.008
MOR		425 MPa		Refractive Index vs. Chromium Concentration	3 x 10^-3 (Δn / % Cr_2O3)
Compressive Strength		2.0 Gpa		Fluorescent Lifetime at 0.05% Cr_2O3	3 ms at 300 K
Hardness		9 Mhos, 2000 Knoop		Fluorescent Linewidth (R₁)	5.0 Å at 300K
Thermal Expansion	20° to 50° C	5.8 x 10-6 / ° C		Output Wavelength (R₁)	6.94.3 nm
Thermal Expansion	20° to 200° C	7.7 x 10-6 / ° C		Major Pump Bands	404 nm and 554 nm
Thermal Conductivity	at 0° C	46.02 W / (m•K)
	at 100° C	25.10 W / (m•K)
	at 400° C	12.55 W / (m•K)	All values are for 60° orientation material

Material and Fabrication Specification

Material
Crystallographic orientation, optical (c - axis) to rod axis			60° within 5°
Dopant Concentration: Cr₂O₃ Weight Per Cent Substitution for Al₂O₃			0.05% ± 0.005%
			0.03% ± 0.005%
Optical Quality, Double - Pass Interferometer set for minimum fringes in rod, all diameters to 1.00" (25.4 mm)		SIQ GRADE	SELECT GRADE
		0.5 fringes / inch of length	0.25 fringes / inch of length
Corefree Diameter		0.756" and smaller	0.625" and smaller
Bubbles, inclusions, scattering sites as viewed in white,focused illuminator light and under crossed polarisers		Free of imperfections visible to the naked eye
				Fabrication
Diameter Tolerance			± 0.001" (0.025 mm)
Length Tolerance		(Plano / Plano)	± 0.030" (0.75 mm)
Barrel Finish - Standard			30 microinch CLA
Polished Barrel Finish - Special Order			80 - 50
End Face Bevel		0.005" / 0.010" (0.1 / 0.25 mm) non - focusing radius type;bevel to 0.013" allowed to remove chips on large rods
				Chips	None on polished and faces. Up to 0.012" (0.3 mm) allowed to lie in area of bevel and extend into barrel surface
Flatness	Rod Diameters 0.590" (15 mm) and smaller	1 / 10th wave over 90% of diameter
	Rod Diameter 0.625" (16 mm) and larger	<1 / 5th wave over 90% of diameter
Parallelism of ends faces (measured geometrically with autocollimator and precision rotary table; 2 readings 90° rotation)

Plano / Plano			10 seconds of arc or less
Wedge / Wedge			20 seconds of arc or less
Brewster / Brewster			30 seconds of arc or less
Perpendicularity of end faces to rod axis		Standard	5 minutes of arc or less
		Special Order	2 minutes of arc or less
Surface Finish (viewed in low - angle, reflected light from high - intensity		Standard	20 - 10
microscope illuminator with condenser, by naked eye and 5X loupe)		Special Order	10 - 5
Brewster Angle			20° 34'
Brewster Angle Tolerance			± 30 minutes
Wedge Angle			15' to 8°
Wedge Angle Tolerance			± 10 minutes
Anti - Reflection Coating		Single layer magnesium fluoride, suitable for high power laser operation. Reflectivity at 694 nm is less than 0.25% per end face.
					Meets adherence and abrasion resistance of MIL - C - 48497

_{Information reproduced by kind permission of Saint-Gobain
Crystals & Detectors.
Specification
subject to change without
notice.} _{© Roditi International 2007}