Abstract-Quantum cascade laser-pumped terahertz molecular lasers: frequency noise and phase-locking using a 1560 nm frequency comb

Jean-Francois Lampin, Antoine Pagies, Giorgio Santarelli, Jeffrey Hesler, Wolfgang Hansel, Ronald Holzwarth,  Stefano Barbieri,

(a) Energy diagram of the levels relevant for laser operation. (b) Schematic of the QCL-pumped ML. The laser cavity is closed at one end (left) by an output coupler, obtained by depositing a metallic grid on a Silicon substrate, and on the other end (right) by a plane metallic mirror, with a 1.2 mm hole drilled in its center. An isolator (∼30 dB isolation, and ∼60% transmission) is used to reduce the optical feedback on the DFB QCL. (c) THz ouput power vs MIR pump power, measured without the optical isolator displayed in panel (b). Inset: intensity plot of the optical beam collected with a microbolometer camera positioned at about 4 cm from the laser output coupler.

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-28-2-2091

We report the measurement of the frequency noise power spectral density (PSD) of a Terahertz (THz) molecular laser (ML) pumped by a mid-infrared (MIR) quantum cascade laser (QCL), and emitting 1 mW at 1.1THz in continuous wave. This is achieved by beating the ML frequency with the 1080th harmonic of the repetition rate of a 1560 nm frequency comb (FC). We find a frequency noise PSD < 10Hz2/Hz (-95dBc/Hz) at 100kHz from the carrier. To demonstrate the effect of the stability of the pump laser on the spectral purity of the THz emission we also measure the frequency noise PSD of a CO2-laser-pumped 2.5THz ML, reaching 0.1Hz2/Hz (-105dBc/Hz) at 40kHz from the carrier, limited by the frequency noise of the FC harmonic. Finally, we show that it is possible to actively phase-lock the QCL-pumped molecular laser to the FC repetition rate harmonic by controlling the QCL current, demonstrating a sub-Hz linewidth.

© 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Quantum cascade laser-pumped terahertz molecular lasers: frequency noise and phase-locking using a 1560nm frequency comb

Jean-Francois Lampin, Antoine Pagies, Giorgio Santarelli, Jeffrey Hesler, Wolfgang Hänsel, Ronald Holzwarth, Stefano Barbieri

https://arxiv.org/abs/1911.06568

The recent demonstration of a terahertz (THz) molecular gas laser pumped by a mid-infrared quantum cascade laser (QCL) has opened up new perspectives for this family of sources, traditionally relying on CO2-laser pumping. A so far open question concerning QCL-pumped THz molecular lasers (MLs) is related to their spectral purity. Indeed, assessing their frequency/phase noise is crucial for a number of applications potentially exploiting these sources as local oscillators. Here this question is addressed by reporting the measurement of the frequency noise power spectral density (PSD) of a THz ML pumped by a 10.3{\mu}m-wavelength QCL, and emitting 1mW at 1.1THz in continuous wave. This is achieved by beating the ML frequency with the 1080th harmonic of the repetition rate of a 1560nm frequency comb. We find a frequency noise PSD < 10Hz2/Hz (-95dBc/Hz) at 100kHz from the carrier. To demonstrate the effect of the stability of the pump laser on the spectral purity of the THz emission we also measure the frequency noise PSD of a CO2-laser-pumped 2.5THz ML, reaching 0.1Hz2/Hz (-105dBc/Hz) at 40kHz from the carrier, limited by the frequency noise of the frequency comb harmonic. Finally, we show that it is possible to actively phase-lock the QCL-pumped molecular laser to the frequency comb repetition rate harmonic by controlling the QCL current, demonstrating a sub-Hz linewidth.

Abstract-Advances in terahertz solid-state physics and devices

Journal of Applied Physics

Jeffrey Hesler, Rohit Prasankumar, Jerome Tignon


https://aip.scitation.org/doi/full/10.1063/1.5122975

Terahertz (THz) science and technology have attracted tremendous attention owing to their potential applications in areas including high-speed communications, nondestructive evaluation, biological and medical sensing, and national security.1,2 Terahertz waves bridge electronics and photonics, as well as classical and quantum physics, making them equally attractive for fundamental studies of novel physical phenomena. To realize a broad range of real terahertz applications, it is essential to develop compact solid- state devices for terahertz sources, detectors, modulators, and compact systems. These devices often employ quantum materials and heterostructures and can incorporate other features including carrier transfer using atomic layer epitaxy, micro- and electromechanical systems, plasmonic resonators, and metamaterials. To optimize these devices, we have to understand and control ultrafast carrier dynamics in these advanced materials. Therefore, we have organized a Special Topic in the Journal of Applied Physics to highlight the state-of-the-art in terahertz solid-state devices while also unveiling the properties of these materials on an ultrafast timescale.

Abstract-All-electronic terahertz nanoscopy

Clemens Liewald, Stefan Mastel, Jeffrey Hesler, Andreas J. Huber, Rainer Hillenbrand, and Fritz Keilmann

https://www.osapublishing.org/optica/abstract.cfm?uri=optica-5-2-159&origin=search

Probing conductivity in a contactless way with nanoscale resolution is a pressing demand in such active fields as quantum materials, superconductivity, and molecular electronics. Here, we demonstrate a laser- and cryogen-free microwave-technology-based scattering-type scanning near-field optical microscope powered by an easily aligned free-space beam with a tunable frequency up to 0.75 THz. It uses Schottky diode components to record background-free amplitude and phase nano-images, for the first time in the terahertz range, which is uniquely sensitive for assessing conduction phenomena. Images of Si with doped nanostructures prove a conductance sensitivity corresponding to 1016  cm−3${10}^{16}{\mathrm{cm}}^{-3}$ mobile carriers, at 50 nm spatial resolution.

© 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

MICS Seminar - Recent Developments of Terahertz Mixers and Analyzers at Virginia Diodes

http://www.ece.vt.edu/news/extended.php?id=1510

3:00 PM - 4:00 PM on Friday, November 7, 2014
Location: Whittemore 654 (6th Floor Conference Room)

This talk will focus on two recent THz projects at Virginia Diodes.

Terahertz technology is an emerging field that has a wide range of applications ranging from scientific applications such as astronomy, molecular spectroscopy and fusion plasma diagnostics, to newly developing commercial applications including communications and imaging.

First, Dr. Jeffrey Hesler will describe the development of a 1.46 THz Schottky diode receiver for use in astronomical measurements at the South Pole. The basic technology of the receiver and the system development at VDI will be described. The receiver is now being successfully used at the South Pole for observations by researchers from the University of Arizona.

Then, Dr. Hesler will describe recent developments in THz material-measurements. A 1.1 THz vector network analyzer was used with a quasi-optical setup to characterize dielectric materials. The THz extender hardware, the calibration algorithm and measurement results using the system will be presented.

Speaker Bio: Jeffrey L. Hesler is the Chief Technology Officer of Virginia Diodes and a Visiting Research Assistant Professor at the University of Virginia. His career is focused on the creation of new technologies that are making possible the full exploitation of the Terahertz frequency band for scientific, defense and industrial applications. He has published over 125 technical papers in refereed international conferences and journals, given talks at THz-focused workshops at conferences such as IMS & EuMW, and serves as a reviewer for a variety of IEEE & IEE journals. Dr. Hesler is also the Secretary of the IEEE P1785 Workgroup on Waveguides for Millimeter and Sub-Millimeter Wavelengths (grouper.ieee.org/groups/1785).

Virginia Diodes Dr. Jeffry Hesler presents webinar

http://www.eetimes.com/electrical-engineers/education-training/webinars/4391404/Taking-the-mystery-out-of-mmwave-and-Terahertz-frequency-measurements

Taking the mystery out of mmwave and Terahertz frequency measurements

Date / Time

GMT Standard Time
Thu, Aug 23, 2012 06:00 PM

Eastern Daylight Time
Thu, Aug 23, 2012 02:00 PM

Pacific Daylight Time
Thu, Aug 23, 2012 11:00 AM

Time Zone Converter

System Requirements

Agilent Technologies, Electro Rent

Duration:60 minutes

Overview:
Development work on very high frequency devices and metamaterials has been limited by the difficulty in making good tests. Developers and users of amplifiers, mixers, filters, detectors, receivers, radios and metamaterials at these frequencies need tools for making critical measurements at mmwave and higher frequencies. This webinar show how instruments you are familiar with including Vector Network Analyzers, Signal Analyzers and Sources can be extended in frequency to make a variety of precision measurements at Gigahertz to Terahertz frequencies.

What attendees will learn:

• Key applications using mmwave to Terahertz frequencies
• Challenges in making measurements at very high frequencies
• Measurement capabilities available
• Test setups for component and metamaterial measurements

Presenter:
Dr. Jeffrey L. Hesler, Chief Technology Officer, Virginia Diodes, Inc.
Dr. Jeffrey L. Hesler received the B.S.E.E. in 1989 from Virginia Tech and the Ph.D. in 1996 from the University of Virginia. He is member of the Board of Directors and shareholder of Virginia Diodes, Inc. and serves as Chief Technology Officer of the corporation. In addition, he is affiliated with the University of Virginia as a Visiting Research Assistant Professor in the Department of Electrical and Computer Engineering.