|
|
 |
|
|
Research Interests and Projects
THz Quantum-Cascade Lasers
Quantum cascade (QC) lasers are based upon engineering semiconductor quantum wells with the precision of a single atomic monolayer to provide materials which exhibit optoelectronic properties not found in nature. Specifically, the engineering of "artificial molecules” to control wavefunctions, electronic energies, electron tunneling, and electron scattering probabilities allows us to develop semiconductor lasers in the THz frequency range - one of the last unconquered spectral regions. THz QC-lasers are the only solid-state source of continuous-wave radiation in the 1-5 THz range that can provide milliwatts or more of output power. Ongoing research involves engineering of novel designs for high-temperature, high-power, and low-frequency operation. This work is performed in collaboration with Northrop Grumman Aerospace Systems (Redondo Beach, CA), who is performing molecular beam epitaxial growth of the QC-laser materials.
|
|
|
|
A review paper on THz quantum-cascade lasers.
|
|
Other selected papers
- B. S. Williams, H. Callebaut, S. Kumar, Q. Hu and J. L. Reno, "3.4-THz quantum cascade laser based on longitudinal-optical-phonon scattering for depopulation." Applied Physics Letters, vol. 82, no. 7, 17 Feb. 2003, pp. 1015-7. [PDF]
- B. S. Williams, S. Kumar, H. Callebaut, Q. Hu and J. L. Reno, "Terahertz quantum-cascade laser at l ~ 100 mm using metal waveguide for mode confinement." Applied Physics Letters, vol. 83, no. 11, 15 Sept. 2003, pp. 2124-6.
- B. S. Williams, S. Kumar, Q. Hu and J. L. Reno, "Operation of terahertz quantum-cascade lasers at 164 K in pulsed mode and 117 K in continuous-wave mode." Optics Express, vol. 13, no. 9, 3 May 2005, pp. 3331. [PDF]
- B. S. Williams, S. Kumar, Q. Hu and J. L. Reno, "High-power terahertz quantum-cascade lasers." Electronics Letters, vol. 42, no. 2, 19 January 2006, pp. 89-90. [PDF]
|
|
|
|
Active Terahertz Metamaterials
Electromagnetic metamaterials are constructed from dielectric, metallic, and plasmonic elements with deep subwavelength dimensions engineered to provide properties not found in nature - such as negative refractive index, or optical magnetism. We are investigating the development of metamaterials that are integrated with THz gain media and other active structures that will enable novel optoelectronic devices and functionality, such as laser cavities that exhibit zero index of refraction, highly directional THz antennas, materials and devices with dynamically tunable characteristics. This work is a collaboration with Prof. Tatsuo Itoh and Northrop Grumman Aerospace Systems.
|
|
|
|
THz active composite right/left handed metamaterial waveguide leaky wave antenna
|
|
|
|
Selected publications:
- A. A. Tavallaee, P. Hon, K. Mehta, T. Itoh, and B. S. Williams, "Zero-Index Terahertz Quantum-Cascade Metamaterial Lasers," IEEE J. Quantum Electronics, vol. 46, no 7, July 2010, pp 1091-1098. (paper covered in Nature Photonics "Research Highlights July 2010) [PDF]
- Z. Liu, P. W. C. Hon, A. A. Tavallaee, T. Itoh, and B. S. Williams, "Terahertz composite right/left handed transmission line metamaterial waveguides," Applied Physics Letters vol 100, 071101 February 13, 2012. [PDF]
- P. W. C. Hon, Z. Liu, T. Itoh, and B. S. Williams, "Leaky and bound modes in terahertz metasurfaces made of transmission-line metamaterials," Journal of Applied Physics vol 113, 033105, January 18 2013.[PDF]
- A. A. Tavallaee, P. W. C. Hon, Q.-S. Chen, T. Itoh, and B. S. Williams, "Active terahertz quantum-cascade composite right/left-handed metamaterial," Appl. Phys. Lett. vol 102 021103 January 14 2013.[PDF]
|
|
|
|
Micromachined and integrated antennas for THz QC-lasers
The best performing THz QC-lasers use metal-metal waveguides with dimensions (~10 mm) much smaller than the wavelength (l~60-300 mm). While these waveguides provide excellent temperature and threshold performance, their sub-wavelength dimension results in highly divergent beams and highly reflective facets, which lead to sub-optimal coupling efficiencies. In other words, only a small fraction of the generated THz photons are usable. We are investigating micromachined waveguides and integrated antennas suitable for use with THz QC-lasers to obtain improved beam quality, coupling efficiency, and power output.
|
|
|
|
|
|
|
|
|
|
|
|
|
|
 |
|
|
|
|
|
|
|
 |
|
 |
|
|
|
|
|
|
|
|
Selected publications:
- A. A. Tavallaee, B. S. Williams, P. W. C. Hon, T. Itoh, and QiSheng Chen, "Terahertz quantum-cascade laser with active leaky-wave antenna," Applied Physics Letters vol. 99, 141115 October 7, 2011. [PDF]
- P. W. C. Hon, A. A. Tavallaee, QiSheng Chen, B. S. Williams, and T. Itoh, "Radiation Model for Terahertz Transmission-Line Metamaterial Quantum-Cascade Lasers," IEEE Trans. Terahertz Science and Technology, vol. 2, no 3, pp. 323-332, May 2012. [PDF]
|
|
|
|
|
Semiconductor Nanowire Heterostructures for THz and infrared optoelectronics
Semiconductor nanowires with axial and core-shell heterostructures are excellent candidates for future optoelectronic materials in the THz and mid-IR spectral ranges. We are interested in optoelectronic devices based upon intersubband/level transitions that take place between states formed by the growth of quantum wells and quantum dots within nanowires. Such structures offer unique opportunities for quantum engineering of electronic and phonon states that may lead to high efficiency and high temperature lasers, emitters, detectors in the infrared and THz spectral ranges. This work is a collaboration with the group of Prof. Diana Huffaker at UCLA
|
|
|
|
|
|
|
|
 |
|
|
|
|
|
|
Selected publications:
- P. Senanayake, C.-H. Hung, J. Shapiro, A. Lin, B. Liang, B. S. Williams, D. Huffaker, "Surface plasmon enhanced nanopillar photodetectors," Nano Letters vol 11, pp. 5279-5283, 2011. [PDF]
- P. Senanayake, C.-H. Hung, J. Shapiro, A. Scofield, A. Lin, B. S. Williams, D. L. Huffaker, "3D Nanopillar optical antenna photodetectors," Opt. Express vol 20, pp. 25489-25496, 2012. [PDF]
|
|
|
|
High-Efficiency Mid-infrared Quantum-Cascade Lasers
Our group is investigating high efficiency and high power quantum-cascade lasers that operate in the mid-IR spectral range (3.8-12 mm).
|
|
|
|
Selected publications:
- C. A. Wang, A. Goyal, R. Huang, J. Donnelly, D. Calawa, G. Turner, A. Sanchez-Rubio, A. Hsu Q. Hu, B. Williams, "Strain-compensated GaInAs/AlInAs/InP quantum cascade laser materials,", J. Crystal Growth, vol. 312, pp.1157-1164 (2009).
|
|
|
|
Funding
UCLA Henry Samueli School of Engineering and Applied Science Fellowship
Defense Advanced Research Projects Agency (DARPA)
National Science Foundation (NSF)
Jet Propulsion Laboratory (SURP Program)
Center on Functional Engineered Nano Architectonics (FENA)
Army Research Office (ARO) STTR program
|
|
