US Patent- Terahertz quantum cascade laser implementing a {hacek over (C)}erenkov difference-frequency generation scheme

United States Patent 9711948
Inventors

Belkin, Mikhail (Austin, TX, US) 
Adams, Robert (Austin, TX, US)
Amann, Markus Christian (Garching, DE)
Vizbaras, Augustinas (Garching, DE)

http://www.freepatentsonline.com/9711948.html

A terahertz source implementing a {hacek over (C)}erenkov difference-frequency generation scheme in a quantum cascade laser. The laser includes an undoped or semi-insulating InP substrate with an exit facet that is polished at an angle between 10° to 40°. The laser further includes a first waveguide cladding layer(s) in contact with an active layer (arranged as a multiple quantum well structure) and a current extraction layer on top of the substrate. Furthermore, the laser includes a second waveguide cladding layer(s) on top of the active layer, where the first and second waveguide cladding layers are disposed to form a waveguide structure by which terahertz radiation generated in the active layer is guided inside the laser. The terahertz radiation is emitted into the substrate at a {hacek over (C)}erenkov angle relative to a direction of the nonlinear polarization wave in the active layer, and once in the substrate, propagates towards the exit facet.

Abstract-Broadly tunable terahertz generation in mid-infrared quantum cascade lasers

http://www.nature.com/ncomms/2013/130617/ncomms3021/full/ncomms3021.html

Karun Vijayraghavan,^, Yifan Jiang , Min Jang ,  Aiting Jiang, Karthik Choutagunta^, , Augustinas Vizbaras, Frederic Demmerle^,, Gerhard Boehm , Markus C. Amann^,  Mikhail A. Belkin

Room temperature, broadly tunable, electrically pumped semiconductor sources in the terahertz spectral range, similar in operation simplicity to diode lasers, are highly desired for applications. An emerging technology in this area are sources based on intracavity difference-frequency generation in dual-wavelength mid-infrared quantum cascade lasers. Here we report terahertz quantum cascade laser sources based on an optimized non-collinear Cherenkov difference-frequency generation scheme that demonstrates dramatic improvements in performance. Devices emitting at 4 THz display a mid-infrared-to-terahertz conversion efficiency in excess of 0.6 mW W⁻² and provide nearly 0.12 mW of peak power output. Devices emitting at 2 and 3 THz fabricated on the same chip display 0.09 and 0.4 mW W⁻² conversion efficiencies at room temperature, respectively. High terahertz-generation efficiency and relaxed phase-matching conditions offered by the Cherenkov scheme allowed us to demonstrate, for the first time, an external-cavity terahertz quantum cascade laser source tunable between 1.70 and 5.25 THz.

Abstract-Terahertz quantum cascade laser sources based on Čerenkov difference-frequency generation

http://proceedings.spiedigitallibrary.org/proceeding.aspx?articleid=1380680
Karun Vijayraghavan ; Augustinas Vizbaras ; Robert W. Adams ; Min Jang ; Christian Grasse ; Gerhard Boehm ; Markus C. Amann ; Mikhail A. Belkin
Room-temperature terahertz (THz) quantum cascade laser (QCL) sources based on intra-cavity difference-frequency generation (DFG) with record THz conversion efficiencies is reported. THz DFG QCLs reported previously are highly inefficient since THz radiation produced more than ~100 μm away from the exit facet is fully absorbed due to high THz losses in the QCL waveguide. Our lasers use a non-collinear Čerenkov DFG scheme to extract THz radiation from the active region. Dual-color mid-infrared quantum cascade lasers with integrated giant optical nonlinearity are grown on semi-insulating (S.I.) InP substrates. A lateral current extraction scheme is used. THz radiation is emitted at an angle into the substrate with respect to the mid-infrared pumps. Since S.I. InP is virtually lossless to THz radiation, this scheme allows for efficient extraction of THz radiation along the whole waveguide length. As a result, our sources demonstrate large mid-infrared-to-THz conversion efficiency and directional THz output. Experimentally, proof-of-principle devices demonstrate a conversion efficiency up to 70 μW/W2 and provide output across a 1.2 - 4.5 THz spectral range.© (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.