Selection of Optimum Nonlinear Crystals for Efficient Parametric Generation and Sensitive Detection of Monochromatic ns
- PDF / 372,558 Bytes
- 12 Pages / 612 x 792 pts (letter) Page_size
- 71 Downloads / 173 Views
1016-CC02-01
Selection of Optimum Nonlinear Crystals for Efficient Parametric Generation and Sensitive Detection of Monochromatic ns THz Pulses Yujie J. Ding Electrical and Computer Engineering, Lehigh University, 19 Memorial Drive West, Bethlehem, PA, 18015 ABSTRACT We report our recent progress made on the development of widely-tunable monochromatic THz sources. They have been realized based on difference-frequency generation (DFG) in GaSe, ZnGeP2, and GaP crystals, respectively. Using a GaSe crystal, the output wavelength was tuned continuously in the range from 66.5 µm to 5664 µm (from 150 cm-1 to 1.77 cm-1) with the peak power reaching 389 W. Such a high peak power corresponds to a conversion efficiency of ∼ 0.1% (a photon conversion efficiency of 19%). A further optimization on the THz beam parameter may result in an output peak power of a few kW. Within the range of 100-250 µm the output peak powers were higher than 100 W. We have also investigated THz frequency upconversion in GaSe, ZnGeP2, and GaP crystals. Such a parametric process has a potential for detecting THz pulses at room temperature or just using a thermoelectric cooler. The minimum detectable energy per pulse was measured to be 245 pJ, which corresponds to a noise equivalent energy of 77.5 pJ/ Hz . A further optimization of the process can reduce this value down to 1 pJ/ Hz . INTRODUCTION Transition frequencies between two rotational states in gases are usually within the THz frequency domain [1]. In contrast, most molecules in the domains from visible to mid-infrared exhibit the congested and unresolved ro-vibrational transition peaks [2]. Secondly, THz waves could be used to fingerprint airborne bio particles. Since almost all the aerosol particles have diameters ≤ 10 µm [3], the scattering of the THz waves by the particles suspended in the air could be minimized. Thirdly, due to the presence of the atmospheric windows which mainly originate from the absorption dips of the water vapor, monochromatic THz waves could be eventually used for probing as well as imaging for the ranges of 100 m and farther. Among different schemes for THz generation, parametric processes in nonlinear crystals represent an efficient route for converting optical pulses to the monochromatic THz counterparts. Recently, by mixing two coherent infrared laser beams in nonlinear crystals such as GaSe [4-6],
ZnGeP2 [7-9], and GaP [10,11], we efficiently generated the THz waves with extremely-wide tuning ranges and very high peak powers as well as high conversion efficiencies. The widest tuning range achieved by us covers the wavelengths anywhere from 66.5 µm to 5.66 mm (from 4.51 THz down to 53 GHz). On the high-frequency side of the reststrahlen band, we were able to generate the radiation tunable in the range of 2.7−28.7 µm using a different phase-matching configuration [12]. One can see that the tuning range achieved by us almost covers the entire THz region (0.1-10 THz) and part of the millimeter-wave or microwave domain, i.e. 1 mm to 5.66 mm (53-300 GHz). The highest o
Data Loading...
