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Proposals Accepted: February 28, 2011 - March 30, 2011
Program: STTR
Topic Number: A11a-T005 (Army)
Title: Deep ultraviolet laser for Raman spectroscopy
Research & Technical Areas: Chemical/Bio Defense, Sensors
Acquisition Program:
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,[6] and multiply-ionized gas lasers.[7] 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’s 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: [1] See, for example, http://www.coherent.com.
[2] See, for example, http://www.lumonics.com or http://www.lightmachinery.com.
[3] 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).
[4] J. Sakuma, Y. Asakawa, T. Imahoko, M. Obara, Opt. Lett. 29, p. 1096 (2004).
[5] A. Duebubgm, S. NcKean, A. Starodoumov, Proc. of SPIE 7195, p. 71950H-1
(2009).
[6] T.Takano, Y. Narita, A. Horiuchi, and H. Kawanishi, Appl. Phys. Lett. 84, p.
3567 (2004).
[7] J.B. Marling, IEEE J. Quantum Electronics, QE-11, p. 822 (1975).
Keywords: Deep ultraviolet laser, Raman spectroscopy