Erik W. Young

Nonequilibrium many-body theory of intersubband lasers

We present a theory for intersubband lasers, based on the solution of the Maxwell-semiconductor Bloch equations for the laser field and active medium. The collision contributions are treated within the relaxation rate approximation, where the relaxation rates are determined by microscopic scattering calculations. The theory is suitable for investigating steady-state as well as dynamical laser characteristics. As examples of applications of the theory, we examine the thermal dependence of the laser output versus current density curve and the response to modulation of the injection current, for a three-subband laser. The influence of the nonparabolicity of the conduction band and Hartree-Fock many-body effects are investigated.

Heterodyne Mixing of Terahertz Quantum Cascade Lasers Using a Planar Schottky Diode

Terahertz quantum cascade lasers (QCLs) have been used together with a monolithic planar Schottky diode receiver to study the heterodyne mixing between dual internal modes of a QCL and between a single mode of a QCL and a known molecular line from a molecular gas laser. Dual-mode mixing shows that the intrinsic linewidth of a free-running QCL is les30 kHz . Mixing against a molecular laser line gives a high precision measurement of a QCLs absolute frequency and can show transient turn-on behavior in a pulsed QCL.

Terahertz quantum cascade laser integration with on-chip micromachined rectangular waveguides

Integration of THz quantum cascade lasers (QCLs) with single-mode 75 μm x 37 μm rectangular waveguide components, including horn antennas, couplers, and bends, for operation at 3 THz has been designed and fabricated using thick gold micromachining. Measurements on the isolated waveguide components exhibit fairly low loss and integration with THz QCLs has been demonstrated. This technology offers the potential for realizing miniature integrated systems operating in the 3 THz frequency range.

Gain without Inversion: An Approach for THz Quantum Cascade Laser?

Using a microscopic theory based on the Maxwell-semiconductor Bloch equations, we investigate the possibilities of optically driven QCLs. We show that in a four level cascaded-emission scheme, quantum coherence effects can yield gain without inversion

External Modulation of Terahertz Quantum Cascade Lasers Using Metamaterials

We use active metamaterials as external modulators for a 2.4 THz quantum cascade laser. We present initial optical modulation results with the goal of designing an electrically-driven modulator.

Linear and nonlinear responses of intersubband lasers

We present a many-body theory for intersubband lasers, based on the Maxwell-semiconductor Bloch equations and detailed treatment of scattering processes. Applications involving high excitation and fast modulation conditions are presented.

LDRD final report on high power broadly tunable Mid-IR quantum cascade lasers for improved chemical species detection.

The goal of our project was to examine a novel quantum cascade laser design that should inherently increase the output power of the laser while simultaneously providing a broad tuning range. Such a laser source enables multiple chemical species identification with a single laser and/or very broad frequency coverage with a small number of different lasers, thus reducing the size and cost of laser based chemical detection systems. In our design concept, the discrete states in quantum cascade lasers are replaced by minibands made of multiple closely spaced electron levels. To facilitate the arduous task of designing miniband-to-miniband quantum cascade lasers, we developed a program that works in conjunction with our existing modeling software to completely automate the design process. Laser designs were grown, characterized, and iterated. The details of the automated design program and the measurement results are summarized in this report.

LDRD final report on continuous wave intersubband terahertz sources.

There is a general lack of compact electromagnetic radiation sources between 1 and 10 terahertz (THz). This a challenging spectral region lying between optical devices at high frequencies and electronic devices at low frequencies. While technologically very underdeveloped the THz region has the promise to be of significant technological importance, yet demonstrating its relevance has proven difficult due to the immaturity of the area. While the last decade has seen much experimental work in ultra-short pulsed terahertz sources, many applications will require continuous wave (cw) sources, which are just beginning to demonstrate adequate performance for application use. In this project, we proposed examination of two potential THz sources based on intersubband semiconductor transitions, which were as yet unproven. In particular we wished to explore quantum cascade lasers based sources and electronic based harmonic generators. Shortly after the beginning of the project, we shifted our emphasis to the quantum cascade lasers due to two events; the publication of the first THz quantum cascade laser by another group thereby proving feasibility, and the temporary shut down of the UC Santa Barbara free-electron lasers which were to be used as the pump source for the harmonic generation. The development efforts focused on two separate cascade laser thrusts. The ultimate goal of the first thrust was for a quantum cascade laser to simultaneously emit two mid-infrared frequencies differing by a few THz and to use these to pump a non-linear optical material to generate THz radiation via parametric interactions in a specifically engineered intersubband transition. While the final goal was not realized by the end of the project, many of the completed steps leading to the goal will be described in the report. The second thrust was to develop direct THz QC lasers operating at terahertz frequencies. This is simpler than a mixing approach, and has now been demonstrated by a few groups with wavelengths spanning 65-150 microns. We developed and refined the MBE growth for THz for both internally and externally designed QC lasers. Processing related issues continued to plague many of our demonstration efforts and will also be addressed in this report.