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. 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.
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 Cr2O3 for Al2O3. 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° | 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
/ % Cr2O3) |
||
| Compressive Strength | 2.0 Gpa | Fluorescent Lifetime at 0.05% Cr2O3 | 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 | |
| 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 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 |
|||
