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Many bio-molecules absorb light in the UV range and fluoresce under the beam of a laser. Because of this attribute, UV optical lasers can be used in analytical devices for the biotechnology, pharmaceutical, and medical markets, solid-state white lighting, sterilization and disinfectant devices, and water purification systems. It has been a longstanding goal to shrink the large and expensive lasers that are currently used in such systems.
The wavelength range of 337.5 nm to 450 nm is of interest in the field of spectroscopy for the detection of proteins such as tryptophan, Nicotinamide Adenine Dinucleotide (NADH) and flavin compounds. However, there exists a lack of selectable wavelength laser sources for emitting light in this wavelength range which is affordable.
Army scientists have a solution to the size and price issues in a new device for attaining continuous (CW) and Q-switched (pulsed), UV laser emission in the 337.5 nm to 450 nm wavelength range. The approach leverages the tunable aspect and high gain/high chromium concentration of emerald and transforms it from an expensive, difficult-to-fabricate device into a useful, cost-effective instrument using diode pumped solid state laser (DPSS) construction technology.
A very small high optical-quality emerald crystal ( 2 mm square, 2.5 mm long crystal of chromium doped hydrothermally grown synthetic beryl [Be3Al2(SiO3)6:Cr3+]), that is commercially available is pumped by a common 650 nm red diode laser array (a beta-BaB2O4 (BBO)) or a LiB3O5 (LBO) frequency doubling crystal, which is also about 2 mm square and about 2.5 mm long.
The emerald crystal is coated at the rear face with high-reflection coatings from 729 nm to 809 nm, and from 364 nm to 405 nm, chosen to optimize reflection or transmission for the desired emission wavelength. The 650 nm diode laser array is focused by a lens into the rear of the crystal. While the laser is pumped by the diode laser, a high-power circulating beam exists within a cavity. The second harmonic frequency emerges through the output coating. The peak of the output spectrum lies at approximately 382.5 nm but is wavelength selectable from 364 nm to 405 nm, with decreased output efficiency toward the upper and lower wavelength limit.
The technology may be used for light shows, pathogen detection, encryption, and fluorescence studies.
- Broad applications
- Continuous wave or pulsed
- Businesses can commercialize this technology via an express license from the Army