Research

The Terahertz and Infrared Photonics group is broadly focused on the study of physics and development of novel devices at the intersection of:

  • Engineered quantum electronic properties in low-dimensional semiconductors
  • Engineered electromagnetic metamaterials and artificial structures
  • Development of novel technologies for the generation, detection, and control of THz and mid-IR radiation

The terahertz frequency range lies roughly between 300 GHz and 10 THz (between the microwave and infrared spectra), and remains a challenging spectral region in large part because of the great difficulty in generating and detecting THz radiation. THz radiation is of interest for chemical and biological sensing, security screening, explosive and drug detection, radar, astrophysical probes of the early universe and star formation, combustion sciences, atmospheric sensing, medical imaging, nondestructive evaluation of materials, industrial inspection, probes of condensed matter excitations (e.g. phonons, plasmons, superconductors, magnons, strong light-matter coupling (polaritons)), and short-range high-bandwidth communications.

Self-mixing interferometric effects measured in THz QC-VECSEL for first time

Anthony D. Kim, Daniel McGovern*, and Benjamin S. Williams, “Multi-bounce self-mixing in terahertz metasurface external-cavity lasers,” Optics Express, vol. 32, 18880-18895 (2024). https://doi.org/10.1364/OE.523012

We demonstrate the first THz QC-lasers that operate above 5 THz in continuous-wave mode; in pulsed-mode operation lasing up to 6 THz is observed!

Mohammad Shahili, Sadhvikas J. Addamane, Anthony D. Kim, Christopher A. Curwen, Jonathan H. Kawamura, and Benjamin S. Williams, “Continuous-wave GaAs/AlGaAs quantum cascade laser at 5.7 THz,” Nanophotonics, January 16, 2024. https://doi.org/10.1515/nanoph-2023-0726

Mohammad Shahili, Sadhvikas J. Addamane, Benjamin S. Williams, “GaAs-based Quantum Cascade Laser Emitting above 5 THz,” Infrared Terahertz Quantum Workshop (ITQW), June 25-30, 2023, Erice, Italy. Received Best Paper Award.

QC VECSELs with randomly disordered metasurfaces exhibit multimode and broadband lasing

Eilam Morag, Sandra Li*, Anthony D. Kim, Sadhvikas J. Addamane, Benjamin S. Williams, “Disordered metasurface quantum-cascade VECSELs,” Infrared Terahertz Quantum Workshop (ITQW), June 25-30, 2023, Erice, Italy.
Eilam Morag, Sandra Li*, Anthony Kim, Sadhvikas J. Addamane, Benjamin S. Williams, “THz quantum-cascade VECSELs based upon disordered metasurfaces,” SPIE Photonics West 2023, January 28-February 2, 2023, San Francisco, CA.
*Undergraduate author

BiCMOS THz frequency comb chips from the Babakhani group can emit up to 4 THz

Sidharth Thomas, Sam Razavian, Wei Sun, Benyamin Fallahi Motlagh, Anthony D. Kim, Yu Wu, Benjamin S. Williams, Aydin Babakhani, “A 0.4-4 THz PIN Diode Frequency Multiplier in 90nm SiGe BiCMOS,” IEEE J. Solid. State Circuits, vol. 58, pp 2407-2420,  July 4, 2023. https://doi.org/10.1109/JSSC.2023.3289129

Hybrid electronic-photonic terahertz sources: injection locking of QC-VECSELs using electronic Schottky diode multipliers can stabilize laser frequency fluctuations without need of additional electronics

Christopher A. Curwen, Jonathan H. Kawamura, Darren J. Hayton, Sadhvikas J. Addamane, John L. Reno, Benjamin S. Williams, and Boris S. Karasik, “Optical injection locking of a THz quantum cascade VECSEL with an electronic source,” Optics Letters, vol. 48, pp. 3809-3812, June 12, 2023. June 12, 2023. https://doi.org/10.1364/OL.492182 

QC-VECSELs can be phase-locked to a microwave reference frequency using Schottky diode mixers – a key requirement for stabilized THz local oscillators

Christopher A. Curwen, Jonathan H. Kawamura, Darren J. Hayton, Sadhvikas J. Addamane, John L. Reno, Benjamin S. Williams, and Boris S. Karasik, “Phase locking of THz QC-VECSELs to a microwave reference,” IEEE Transactions of Terahertz Science and Technology, vol. 13, pp. 448 – 453, May 29, 2023. https://doi.org/10.1109/TTHZ.2023.3280451

RF-modulating the electrical bias of a QC-VECSEL at the round trip frequency will cause it to transition from single- to multi-mode emission

Yu Wu, Christopher A. Curwen, John L. Reno, and Benjamin S. Williams, “RF injection locking of THz metasurface quantum-cascade-VECSEL,” Laser and Photonics Reviews, 2023, 230007, March 25, 2023. https://doi.org/10.1002/lpor.202300007

THz quantum-cascade VECSELs can be broadly tunable laser sources

Anthony D. Kim, Christopher A. Curwen, Yu Wu, John L. Reno, Sadhvikas J. Addamane, and Benjamin S. Williams, “Wavelength scaling of widely-tunable terahertz quantum-cascade metasurface lasers,” IEEE Journal of Microwaves, vol. 3, pp 305-318, January 2023. https://doi.org/10.1109/jmw.2022.3224640

First experimental measurement of free-space THz amplification using QC metasurface

Christopher A. Curwen, Sadhvikas J. Addamane, John L. Reno, Mohammad Shahili, Boris S. Karasik, Benjamin S. Williams, and Jonathan H. Kawamura, “Measurement of gain and absorption of a THz quantum-cascade metasurface free-space amplifier,” AIP Advances, vol. 12, 115205 Nov 2, 2022. https://doi.org/10.1063/5.0122154

A cavity with an off-axis-paraboloid mirror within the cryostat results in large QC-VECSEL performance improvements

Yu Wu, Christopher A. Curwen, Darren J. Hayton, John L. Reno, Benjamin S. Williams, “Continuous wave operation of terahertz metasurface quantum-cascade VECSEL with a long intra-cryostat cavity,” Applied Physics Letters, vol. 121, 191106, Nov 11, 2022. https://doi.org/10.1063/5.0107667 

Reducing the thickness of the THz QC-laser active region improves the continuous-wave operating temperature

Christopher A. Curwen, Sadhvikas J. Addamane, John L. Reno, Mohammad Shahili, Jonathan H. Kawamura, Ryan M. Briggs, Boris S. Karasik, and Benjamin S. Williams, “Thin THz QCL active regions for improved continuous-wave operating temperature,” AIP Advances, 11, 125018, 2021. (Editor’s pick) https://doi.org/10.1063/5.0071953 

Measurements of QC patch metasurfaces using THz time-domain spectroscopy show signatures of strong light-matter coupling

Y. Shen, A. D. Kim, M. Shahili, C. A. Curwen, S. Addamane, J. L. Reno, and B. S. Williams, “THz time-domain characterization of amplifying quantum-cascade metasurface,” Applied Physics Letters, vol. 119, 181108 2021. https://doi.org/10.1063/5.0067690

The first demonstration of a QC-VECSEL below 2 THz

Y. Wu, Y. Shen, S. Addamane, J. L. Reno, and B. S. Williams, “Tunable quantum-cascade VECSEL operating at 1.9 THz,” Optics Express, 29, 34695-34706 2021. https://doi.org/10.1364/OE.438636

THz metasurface VECSELs can be coaxed into multi-mode operation by amplitude compensation of the output coupler

Y. Wu,S. Addamane, J. L. Reno, and B. S. Williams, “Multi-mode lasing in terahertz metasurface quantum-cascade VECSELs,” Applied Physics Letters, 119, 111103, 2021. https://doi.org/10.1063/5.0061391 

A coupled-resonator metasurface design exhibits amplification bandwidths over 1 THz

C. A. Curwen, J. L. Reno, and B. S. Williams, “Broadband metasurface design for terahertz quantum-cascade –VECSEL,” Electronics Letters, vol. 56, 1264-1267, 2020. https://doi.org/10.1049/el.2020.1963

Patch-antenna metasurfaces dramatically reduce power consumption of QC-VECSEL lasers

C. A. Curwen, J. L. Reno, and B. S. Williams, “Terahertz quantum-cascade patch-antenna VECSEL with low power dissipation,” Applied Physics Letters, vol. 116, 241103, June 16, 2020. https://doi.org/10.1063/5.0008867

Ultra-short cavity metasurface lasers exhibit record tunability of single mode with high power and excellent beam quality

Broadband tuning of short-cavity THz QC-VECSEL

C. A. Curwen, J. L. Reno, and B. S. Williams, “Broadband continuous single-mode tuning of a short-cavity quantum-cascade VECSEL,” Nature Photonics, vol. 13, 855–859, September 23, 2019. https://doi.org/10.1038/s41566-019-0518-z

This paper was covered in Nature Photonics News&Views: “A wavelength-size tunable Fabry–Pérot laser,” Nathan Jukam, vol 13, pp. 823-825, 2019. https://doi.org/10.1038/s41566-019-0555-7 

Novel density matrix method allows robust simulation of THz quantum-cascade laser performance

B. A. Burnett, A. Pan, C.-O. Chui, B. S. Williams, “Robust Simulation of Terahertz Quantum Cascade Laser Active Regions,” IEEE Trans. Terahertz Science and Technology, vol. 8, 492-501, September 2018. http://dx.doi.org/10.1109/TTHZ.2018.2851396

High-power density metasurface allows QC VECSELs that output over 1 Watt of THz power

Watt-level pulsed output power from THz QC-VECSEL

C. A. Curwen, J. L. Reno, and B. S. Williams, “Terahertz Quantum Cascade VECSEL with Watt-Level Output Power,” Applied Physics Letters, vol. 113, 011104, July 2 2018. https://doi.org/10.1063/1.5033910

Building the external cavity of a THz VECSEL inside a cryostat at 77 K improves operation

L. Xu, C. A. Curwen, J. L. Reno, and B. S. Williams, “High performance terahertz metasurface quantum-cascade VECSEL with an intra-cryostat cavity,” Applied Physics Letters, vol. 111, 101101, Sept. 5 2017. http://dx.doi.org/10.1063/1.4993600 (APL Editor’s Pick)

A new density matrix method allows accurate modeling of coherent quantum transport in THz QC-lasers without resorting to phenomenological localization of wavefunctions

A. Pan, B. A. Burnett, C.-O. Chui, and B. S. Williams, “Density Matrix Modeling of Quantum Cascade Lasers without an Artificially Localized Basis: A Generalized Scattering Approach,” Physical Review B, vol. 96, 085308, August 15, 2017. https://doi.org/10.1103/PhysRevB.96.085308

InAs1−xPx (0 ≤ x ≤ 0.33) nanowire arrays are grown on InP (111)B substrates

D. Ren, A. Farrell, B. S. Williams, D. Huffaker, “Seeding Layer Assisted Selective-area Growth of As-rich InAsP Nanowires on InP Substrates,” Nanoscale, vol. 9, 8220-8228, June 28, 2017. https://dx.doi.org/10.1039/C7NR00948H

Laying out the theory of the metasurface QC-VECSEL

VECSEL on the cover of IEEE JSTQE

L. Xu, C. A. Curwen, D. Chen, J. L. Reno, T. Itoh, and B. S. Williams, “Terahertz metasurface quantum-cascade VECSELs: theory and performance,” IEEE Journal of Selected Topics in Quantum Electronics, (Invited paper) vol. 23, 1200512, Nov.-Dec. 2017. https://doi.org/10.1109/JSTQE.2017.2693024 (featured on cover)

A metasurface engineered with cross-polarized “zig-zag” antennas allows dynamic switching of the laser polarization state

L. Xu, D. Chen*, C. A. Curwen, M. Memarian, J. L. Reno, T. Itoh, and B. S. Williams, “Metasurface quantum-cascade laser with electrically switchable polarization,” Optica, vol. 4, 468-475 (2017). https://doi.org/10.1364/OPTICA.4.000468

*Undergraduate author

Will quantum-dot THz cascade lasers take us to room temperature? Maybe, but new physics will alter the conventional wisdom about QC-laser design.

B. A. Burnett and B. S. Williams, “Design strategy for terahertz quantum dot cascade lasers,” Optics Express vol. 24, 25471-25481, October 31 2016   https://doi.org/10.1364/OE.24.025471

Engineering the phase curvature of a flat QC metasurface allows it to focus and amplify THz light simultaneously. The result: stable laser cavities with near-diffraction limited beams.

L. Xu, D. Chen*, T. Itoh, J. L. Reno, and B. S. Williams, “Focusing metasurface quantum-cascade laser with a near diffraction-limited beam,” Optics Express, vol. 24, 24117-24128 October 17 2016. https://doi.org/10.1364/OE.24.024117

*Undergraduate author

Simulation and design of composite right/left handed metamaterial waveguides based on graphene plasmons

Simulated dispersion from CRLH metamaterial waveguide based upon graphene plasmons.

D. A. Chu*, P. W. C. Hon, T. Itoh, and B. S. Williams, “Feasibility of graphene CRLH metamaterial waveguides and leaky wave antennas,” Journal of Applied Physics, vol. 120, 013103, July 2016. http://dx.doi.org/10.1063/1.4955138

*Undergraduate author

Density matrix model for intersubband transport reveals the origins of the optical nonlinearities in mid-IR QC-lasers

Density matrix model for difference frequency generation processes in quantum-cascade lasers

B. A. Burnett and B. S. Williams, “Origins of terahertz difference frequency susceptibility in mid-infrared quantum cascade lasers,” Physical Review Applied, vol. 5, 034013, March 2016. http://dx.doi.org/10.1103/PhysRevApplied.5.034013

The first metasurface laser: the quantum-cascade VECSEL (vertical external cavity surface emitting laser)

L. Xu, P. W. C. Hon, C. Curwen, Q.-S. Chen, T. Itoh, and B. S. Williams, “Metasurface external cavity laser,” Applied Physics Letters, vol. 107, 221105 (2015) http://dx.doi.org/10.1063/1.4936887

Featured in Physics Today: “Search and Discovery: A quantum cascade laser gets a geometric makeover”. Mark Wilson, February 2016, vol. 69, issue 2, page 16. http://dx.doi.org/10.1063/PT.3.3070 

A review of quantum-cascade lasers in 2015

M. S. Vitiello, G. Scalari, B. S. Williams, and P. DeNatale, “Quantum cascade lasers: 20 years of challenges,” Optics Express, vol. 23, 5167-5182 (2015) http://dx.doi.org/10.1364/OE.23.005167

A density matrix model allows us to model proposed quantum-dot cascade lasers including the effects of strong electron-phonon coupling

B. A. Burnett and B. S. Williams, “Density matrix model for polarons in a terahertz quantum dot cascade laser,” Physical Review B, vol. 90, 155309, 2014. http://dx.doi.org/10.1103/PhysRevB.90.155309

A surface-impedance model describes both TE and TM “spoof-surface-plasmons” that exist on composite-right-left-handed (CRLH) metasurfaces

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. http://dx.doi.org/10.1063/1.4776761

An amplifying composite right/left handed (CRLH) metamaterial leaky-wave antenna is integrated with a THz QC-laser, and exhibits backwards-wave and zero-index operation

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,” Applied Physics Letters vol. 102, 021103, January 14 2013. http://dx.doi.org/10.1063/1.4775666

Modeling to explain operation of plasmonic crystal nanopillar photodetectors

P.  Senanayake, C.-H. Hung, J. Shapiro, A. Scofield, A. Lin, B. S. Williams, D. L. Huffaker, “3D Nanopillar optical antenna photodetectors,” Optics Express vol. 20, pp. 25489-25496, November 5 2012. http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-20-23-25489

Antenna model explains radiation loss from THz QC-laser metal-metal waveguides and leaky-wave antennas

P. W. C. Hon, A. A. Tavallaee, Q.-S. 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. http://dx.doi.org/10.1109/TTHZ.2012.2191023

Winner of 2012 IEEE Transactions on THz Science and Technology Best Paper Award.

Demonstration of composite right/left handed (CRLH) metasurface in terahertz: a platform for negative index wave propagation

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 Feb 13, 2012. http://dx.doi.org/10.1063/1.3684250 

Semiconductor nanopillar photodetectors with plasmonic absorbers

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. http://dx.doi.org/10.1021/nl202732r

A terahertz QC-laser with an integrated leaky wave antenna enables beam steering

A. A. Tavallaee, B. S. Williams, P. W. C. Hon, T. Itoh, and Qi-Sheng Chen, “Terahertz quantum-cascade laser with active leaky-wave antenna,” Applied Physics Letters vol. 99, 141115 October 7, 2011. http://link.aip.org/link/doi/10.1063/1.3648104 

THz QC-laser local oscillator enables heterodyne gas cell spectroscopy

Y. Ren, J. N. Hovenier, R. Higgins, J. R. Gao, T. M. Klapwijk, S. C. Shi, A. Bell, B. Klein, B. S. Williams, S. Kumar, Q. Hu, and J. L. Reno, “Terahertz heterodyne spectrometer using a quantum cascade laser,” Applied Physics Letters, vol. 97, 161105 October 18, 2010.
http://link.aip.org/link/APPLAB/v97/i16/p161105/s1

We conceive and model a “zero-index laser” with uniform modal field for high-efficiency and no spatial hole burning

Simulation of E-field intensity proposed Zero-index QC-laser.

A. A. Tavallaee, P. W. C. 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.   http://dx.doi.org/10.1109/JQE.2010.2043642.

*Undergraduate author

covered in Nature Photonics, Research Highlights, July 2010 vol 4, pp. 408-409 . http://dx.doi.org/doi:10.1038/nphoton.2010.139

Tunable external cavity THz QC-lasers based on Littrow configuration

A. W. M. Lee, B. S. Williams, S. Kumar, Q. Hu, and J. L. Reno, “Tunable Terahertz Quantum Cascade Lasers with External Gratings,” Optics Letters, vol 35, April 1 2010, pp. 910-912.    http://dx.doi.org/10.1364/OL.35.000910

A review article on terahertz quantum-cascade lasers

Benjamin S. Williams, “Terahertz quantum cascade lasers.” Nature Photonics, vol. 1, September 2007, pp. 517-525. (review article) http://dx.doi.org/10.1038/nphoton.2007.166