Friday, January 9, 2015

US Army STTR-Intracavity Nonlinear Optical Generation of THz Radiation

A15A-T003 (Army)
Intracavity Nonlinear Optical Generation of THz Radiation
Dec 14, 2014

Current sub-THz sources utilize Schottky-diode based multipliers for the state-of-the-art performance [1]. On the high frequency side of the “THz gap”, quantum cascade lasers have shown promise; however, only nonlinear optical approaches show promise for RT (room temperature), monolithic multi-mW continuous wave (CW) power levels in the 1-4 THz regime [2-5]. Nonlinear optical generation of 1-6 THz frequency radiation has been achieved through a number of approaches using various materials; however, the efficiency of the nonlinear conversion falls-off in what is known as the “THz gap” around 1 THz. Intracavity generation of THz radiation indicates the possibility of obtaining relatively high power at room temperatures from a monolithic package. Applications of such high power sources to THz spectroscopy [6] and imaging [7] are of interest and hold unexplored potential. Studies of these application fields at high power levels has been limited by the availability of the high power sources. The development of the sources will aid further research of THz techniques and their applications by making them available to leading THz laboratories. Thus, the development of such sources for use and distribution to the leading spectroscopy labs will be part of the commercialization goals in phase II and III. The efficiency, compactness, and high power output are the main considerations with an eye toward manufacturability of a significant number of the sources for use in various THz spectroscopy and imaging laboratories. Although intracavity nonlinear optical generation of THz radiation is the primary approach sought to achieve this goal, alternative approaches will be considered if the monolithic integration of that technology has promise as a next generation technology. 
PHASE I: Using a proposed monolithic design, show evidence of feasibility of all major elements. Develop theoretical estimates with some experimental demonstration of THz signal generation in the proposed materials. Theoretical estimates should indicate the feasibility of 10 mW, CW RT at 4 THz and approximate mW power levels at 1 THz (also CW RT). 
PHASE II: Fabrication and testing of the full monolithic THz source. Optimization of the laser sources and frequency conversion designs should be studied, implemented and tested. The general goals are to demonstrate mWs of power across the 1-4 THz spectrum (CW, RT), and 50 mW of power by the end of the program across at least a portion of the 1-4 THz spectrum. 
PHASE III DUAL USE APPLICATIONS: Terahertz sources have potential uses in both DoD and civilian applications. Monolithically integrated, efficient RT CW radiation in the 1-4 THz regime will be useful for studies of spectroscopic sensing of various chemicals. Imaging in this regime will also be of interest with investment in beam quality which can be further explored with additional Phase III funding. Transition of the high power sources to various laboratories will be sought (DoD, NIST, DoE, universities, etc.) to study potential applications. Dual use applications may include various types of imaging and sensing of unknown and hidden objects, chemicals, and various biomolecules, as well as remote sensing applications in meteorology and climatology.
1. See, for Virginia Diodes, Inc. 2. M.A. Belkin, F. Capasso, A. Belyanin, D.L. Sivco, A.Y. Cho, D.C. Oakley, C.J. Vineis, and G.W. Turner Nature Photon. 1, 288 (2007). 3. M. A. Belkin, F. Capasso, F. Xie, A. Belyanin, M. Fischer, A. Wittmann, and J. Faist, Appl. Phys. Lett. 92, 201101 (2008). 4. K. Vijayraghavan, R.W. Adams, A. Vizbaras, M. Jang, C. Grasse, G. Boehm, M. C. Amann, and M.A. Belkin, Appl. Phys. Lett. 100, 251104 (2012). 5. K. Vijayraghavan, R.W. Adams, A. Vizbaras, M. Jang, C. Grasse, G. Boehm, M. C. Amann, and M.A. Belkin, Nature Comm. 4, 2021 (2013). 6. P. H. Siegel, “THz Technology,” IEEE Trans. Microwave Theory and Techniques 50th Anniversary Issue, vol. 50, no. 3, pp. 910-928, March 2002. 7. K. B. Cooper, R. J. Dengler, N. Llombart, A. Talukder, A. V. Panangadan, C. S. Peay, I. Mehdi, P. H. Siegel, “Fast, high-resolution terahertz radar imaging at 25 meters,” Proc. SPIE v. 7671, 2010.

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