Desert Beam Technologies LLC. is developing a proprietary state-of-the-art room temperature CW TECSEL (Terahertz External Cavity Surface Emitting Laser) source capable of generating mW narrow-line mW level powers at any frequency across and outside the THz gap

Figure 1 Schematic showing THz power performance of different sources around the THz gap. The red rectangle depicts how the TECEL source can span the gap.

Continuous wave (CW) terahertz (THz) sources are highly desirable for a wide range of applications ranging from THz Astronomy above to spectroscopy and biosensing, to security and quality inspection in various industries as well as medical and pharmaceutical applications.  Our THz external cavity surface emitting laser (TECSEL) source, operating at room temperature, is based on intra-cavity difference frequency generation using a periodically poled Lithium Niobate crystal [Scheller et al 2010]. Different nonlinear crystals can be employed in the cavity and designed for either collinear or noncollinear phase matching. The IR dual wavelength high circulating power is generated via an intracavity etalon placed in a high finesse VECSEL cavity. Dual wavelength emission is facilitated by spectral hole burning in the very broad gain of the host semiconductor medium enabling generation of THz frequencies from low frequency (0.1THz) to 5THz and beyond. The choice of circulating IR wavelength is arbitrary and the VCSEL chip can be designed either for IR, visible or mid-IR emission in order to minimize intracavity losses and optimize THz extraction.  A picture of the TECSEL cavity and breadboard set-up is shown in Figure 2 for a noncollinear phase matching geometry.

Figure 2: Illustration of the setup: The pump laser is reflected by the mirror M3 and directed to the VECSEL chip. The cavity is formed by the curved mirror M1 and the flat mirror M2. A Brewster window (BW) and an etalon are placed within the resonator to ensure a linearly polarized emission at two wavelengths. The two laser modes mix inside the nonlinear crystal (NLC) and THz radiation is emitted from the crystal surface, collimated by a cylindrical THz lens. (b): Photograph of the employed setup. The marked parts are 1) the semiconductor VECSEL device, 2) the etalon, 3) the BW 4) M1, 5) the NLC, 6) M2, 7) a cylindrical THz lens, 8) the head of the pump laser and 9) the illustrated circulating IR laser mode.

Our CW source has been demonstrated specifically at 765 GHz, 825GHz (remote explosives detection), 1 THz and 1.9THz (Local oscillator for a 1.9Thz Astronomy receiver). Figure 3 shows preliminary measured performance at 1THz and 1.9Thz , showing the expected quadratic power scaling with both IR circulating power and frequency.

Figure 3: Measured THz output power as function of the total intracavity power of both infrared modes. The THz frequency was 1 THz (triangles) and 1.9 THz (dots).

Desert Beam Technologies LLC’s proprietary TECSEL source can also be operated in pulsed mode to deliver unsurpassed peak powers for Terahertz Time Domain spectroscopy (TDS).

Publications:

1.  Maik Scheller, Joe M. Yarborough, Jerome V. Moloney, Mahmoud Fallahi, Martin Koch, and Stephan W. Koch, "Room temperature continuous wave milliwatt terahertz source," Opt. Express 18, 27112-27117 (2010).

2.  Physics Today, Search & Discovery, “Record Power in the Terahertz Gap”, (to appear): 
     http://blogs.physicstoday.org/update/2011/01/-the-universe-teems-with.html