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Proposals Accepted: February 28, 2011 - March 30, 2011
Topic Number: A11a-T005 (Army)
Title: Deep ultraviolet laser for Raman spectroscopy
Research & Technical Areas: Chemical/Bio Defense, Sensors
Objective: Develop a powerful, long-lived, compact, continuous wave (cw) or quasi-cw deep ultraviolet (200-250 nm) laser suitable for Raman spectroscopy.
Description: Raman spectroscopy has a long history of measuring unique molecular signatures used to recognize various toxins and energetic materials. In many cases, the investigation of such materials is limited to government laboratories because of safety or ITAR restrictions on the release of certain materials to the general public. In addition, there is a growing need to scan over large areas to identify contaminants on surfaces, for which laser power may be traded off for focus and scan speed. Ultraviolet (UV) Raman spectroscopy generates even stronger signals than infrared Raman spectroscopy because of the combined effects of the quartic frequency dependence of the scattering cross section and the possibility of resonance Raman that selectively excites specific molecular functional groups. To gain the maximum enhancement and avoid obfuscating photoluminescence, excitation in the 200-250 nm region is required. Currently, the most commonly used lasers for deep UV Raman spectroscopy are frequency doubled Ar+ lasers (244 nm), excimer lasers (KrF 248 nm), or hollow cathode lasers (HeAg at 224.3 nm or NeCu at 248.6 nm).[1-3] Although powerful, these lasers are not compact, portable, reliable, or sustainable enough to be suitable for field use, so they are not of interest. Quadrupled Nd:YAG and Nd:YLF lasers offer acceptable size, weight, power and performance, but have unacceptable wavelength profiles; 266 and 262 nm respectively. What is needed are powerful, long-lived, narrow line (< 1 cm-1), compact cw or quasi-cw UV lasers operating in the 200-250 nm spectral region. High average power (> 1 milliwatt required, > 50 milliwatts desired), long operational lifetime (> 10,000 hours), non-cryogenic lasers that maintain good beam quality and frequency stability over hours of operation will be strongly favored. Promising approaches emerging from academia and industry include, but are not limited to, frequency multiplied solid state or fiber lasers,[4-5] wide bandgap semiconductor heterostructure emitters, and multiply-ionized gas lasers. If quasi-cw pulsed operation is proposed, the pulses must be long enough that their spectral bandwidth does not interfere with the requirement to perform Raman spectroscopy of least 1 cm-1 accuracy. If cryogenic operation is proposed, the laser must use inexpensive thermoelectric coolers or alternative coolers that do not require liquid cryogens.
PHASE I: Design a powerful, long-lived, narrow line (< 1 cm-1), compact cw or quasi-cw deep UV laser operating in the 200-250 nm region suitable for Raman spectroscopy. Estimate the laser power generated, the wall plug power required, the beam quality, the operational lifetime, and the frequency stability over several hours of continuous operation. If quasi-cw pulsed mode is proposed, specify pulse width and repetition rate. Identify the likely sources of performance degradation and describe plans to overcome them in Phase II.
PHASE II: Construct and deliver to the Army a powerful, long-lived, narrow line (< 1 cm-1), compact cw or quasi-cw UV laser in the 200-250 nm spectral region suitable for Raman spectroscopy. All attendant power supplies and coolers must be included with the delivered laser system. A detailed analysis of the expected power, operational performance degradation, beam quality stability, and frequency stability must be provided to describe the laser抯 operational envelope and confirm the likelihood of stable high average power operation (> 1 mW required, > 50 mW desired) over 10,000 hours. Estimate the unit cost and operating cost of the laser.
PHASE III DUAL USE APPLICATIONS: Commercialization of a compact deep UV laser for Raman and resonance Raman spectroscopy will provide tremendous value to the biochemical and biomedical industries for analysis of a wide variety of organic analytes. There is also a growing interest in analysis of inorganic analytes and nanostructures for various large scale manufacturing processes as well as the development of innovative hybrid materials.
References:  See, for example, http://www.coherent.com.
 See, for example, http://www.lumonics.com or http://www.lightmachinery.com.
 J.A. Piper and C.E. Webb, J. Phys. D: Appl. Phys. 6, p. 400 (1973). D.C. Gerstenberger, R. Solanki, G.J. Collins, IEEE Journal of Quantum Electronics, QE-16, p. 820-834 (1980).
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Keywords: Deep ultraviolet laser, Raman spectroscopy