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08:30-09:30 Session 1: Welcoming remarks and Plenary Talk

Welcoming remarks by the chairs to open the conference, followed by a Plenary Talk by Frank Koppens.

Registration opens at 8:00am.

Welcome and Opening Remarks
Nano-lego for light with (twisted) 2D materials (Plenary Talk)

ABSTRACT. We discuss 2D-material heterostructures as nano-lego for light. In particular, we will show nano-optoelectronic devices that demonstrate the exciting properties of 2D polaritons, such as plasmon, phonon and exciton polaritons, which challenge the limits of quantum light-matter interactions. In addition, quantum confined status can be probed through intersubband transitions in few-layer semiconducting 2D materials. Device applications, such as detectors for infrared and THz light will also be discussed.

09:30-10:30 Session 2: Nanoscopy
THz near-field imaging and spectroscopy with nanoscale spatial resolution
PRESENTER: Tobias Gokus

ABSTRACT. Scattering-type near-field optical microscopy (s-SNOM) can overcome the limits in spatial resolution of conventional THz imaging and spectroscopy techniques. In this talk we presents recent results and important applications of THz imaging and THz time domain spectroscopy with sub-20 nm spatial resolution based on the s-SNOM platform.

Self-mixing optomechanics with nanometer resolution in a Terahertz quantum cascade laser

ABSTRACT. The feasiblity of detecting deeply subwalength vibrations with nanometer precision at terahertz frequencies is demonstrated. This result was achieved using a suspended silicon nitride membrane within a terahertz quantum cascade laser self-mixing apparatus. Besides representing a platform for the characterization of small displacements, this configuration can be exploited for the realization of optomechanical systems where lasers are coupled by a radiation pressure driven mechanical resonator.

Terahertz nanoscopy of non-equilibrium carrier dynamics: A thermometric approach (Invited)
PRESENTER: Qianchun Weng

ABSTRACT. We describe a novel near-field microscope, called terahertz (THz) scanning noise microscope (SNoiM), which maps ultrahigh frequency current fluctuation (15-30 THz) with nanoscale spatial resolution. The SNoiM is demonstrated to be a powerful and unique experimental tool for studying local charge-carrier dynamics in a variety of non-equilibrium systems.

10:30-10:50 Coffee Break

Location: Anacapa Foyer

10:50-12:20 Session 3: THz quantum cascade lasers
High-performance GaAs/AlAs terahertz quantum-cascade lasers
PRESENTER: Lutz Schrottke

ABSTRACT. GaAs/AlAs terahertz quantum-cascade lasers (QCLs) exhibit comparatively high wall-plug efficiencies. They are promising radiation sources for spectroscopic applications, if the output power and operating temperature reach sufficiently high values. We define a practical operating temperature T_po, for which the QCL emits an optical output power of at least 1 mW. For a 4.75-THz QCL, we obtain a maximum value for T_po of 72 K, which can be increased by using an additional back-facet mirror.

Multi-watt terahertz distributed-feedback lasers

ABSTRACT. A phase-locking scheme is developed for monolithic surface-emitting terahertz quantum cascade lasers with hybrid second and fourth-order Bragg gratings that achieves large radiative efficiency, and symmetric, single-lobed radiation patterns with low far-field divergence. Peak output power of 1.88 W is measured for a dual-mode ∼ 3.3 THz laser with 10.6 ◦ × 9.2 ◦ beam divergence, and 1.34 W for a single-mode 3.24 THz laser with 4.6 ◦ × 4.2 ◦ divergence in pulsed mode of operation at ∼ 58 K.

Advances in Terahertz Quantum Cascade Lasers with Room-Temperature Negative Differential Resistance

ABSTRACT. We suggest and demonstrate experimentally a novel split-well direct-phonon (SWDP) scheme for THz-QCLs. As a result of this unique scheme, the lasers benefit from a more flexible design and an efficient isolation of laser levels from excited and continuum states. A clean three-level system, that is, most of the electrons reside in the three lowest subbands even at elevated temperatures, is achieved as indicated by an NDR behavior at room temperature.

Mode Switching of a Dual-color Terahertz Quantum Cascade Laser
PRESENTER: Martin A. Kainz

ABSTRACT. The emission of a THz QCL with two optical transitions is studied. The population of the upper laser states, which correspond to 3.4 THz and 3.8 THz, are investigated for different operating temperatures and in a strong magnetic field, which influences the elastic scattering channel for the two upper laser states and changes the lasing frequency.

Thermoelectrically Cooled Terahertz Quantum Cascade Laser

ABSTRACT. We present the first thermoelectrically (TEC) cooled terahertz quantum cascade laser (QCL). A high temperature 3-well THz QCL is mounted to a novel Peltier cooler and housing. The temperature- and time-dependent laser performance, the TEC characteristics, and the duty cycle are investigated.

Thermo-electrically cooled THz Quantum Cascade Lasers
PRESENTER: Lorenzo Bosco

ABSTRACT. We present THz QCLs which operate from 195 K to 210.5 K on a Peltier cooler, with a peak output power as high as 200 mW at 10 K. The design is based on two quantum wells per period and has been optimized with a nonequilibrium Green’s function model and processed using a dry etched Cu-Cu double-metal waveguide.

12:20-13:30 Buffet Lunch

Location: Anacapa Terrace and Foyer

13:30-15:15 Session 4: THz QCL dynamics and locking
Phase analysis and full phase control of chip-scale infrared frequency combs

ABSTRACT. For high-resolution molecular spectroscopy and metrology applications, infrared frequency combs need a full frequency stabilization of all the emitted modes. Here we demonstrate the full phase stabilization and independent control of the two comb degrees of freedom, offset and mode spacing, of quantum cascade lasers frequency combs. A technique enabling to monitor the obtained degree of coherence is also presented.

Spectrally resolved gain dynamics in THz quantum cascade lasers

ABSTRACT. In this contribution we present our investigations of the gain recovery dynamics of a heterogeneous terahertz quantum cascade laser and their role in the stable operation of a broadband active region. We employ THz-pump/THz-probe time domain spectroscopy (TDS). The measurements reveal a strong coupling between the stacks that lead to the same gain recovery time for each stack although not all of them recover according to a simple exponential curve.

Offset phase-locking of two THz quantum cascade lasers for high dynamic range heterodyne imaging
PRESENTER: Elise Uyehara

ABSTRACT. Here we demonstrate the heterodyne mixing of two unidirectional, 3rd order DFB QCLs with a Schottky diode mixer. The DFB’s are centered around 2.7 THz with a frequency difference of 6-8 GHz. After phase-locking, the stabilized beat note has a narrow linewidth of 0.3 Hz, producing a high dynamic range of 80 dB.

Active harmonic modelocking and self-starting harmonic emission in THz QCLs

ABSTRACT. In laser technology harmonic modelocking is usually employed to attain higher repetition rates. Despite the favourable dynamics of THz QCLs, harmonic active modelocking hasn't been experimentally demonstrated yet. Here we present active modelocking experiments performed at the fundamental and second harmonic on a 6mm THz QCL. We will also show that in certain cases, QCLs can spontaneously attain second or higher harmonic emission without active modulation, i.e. self-starting harmonic behaviour

Light-induced frequency tuning and stabilization of terahertz quantum-cascade lasers
PRESENTER: Martin Wienold

ABSTRACT. We observe continuous frequency tuning over a range of up to 40 GHz by near infrared optical excitation of terahertz quantum-cascade lasers. We developed a model which explains the effect by an optically excited electron-hole plasma. We further exploited the effect for frequency and power stabilization of QCLs.

Terahertz transmission responses of quantum cascade lasers over a wide range of incident electric field amplitude
PRESENTER: Yohei Sakasegawa

ABSTRACT. THz transmission responses of THz-QCLs are studied. Increasing the incident field amplitude the response transfers from the small-signal (gain clamping) regime to a transparent (zero gain) regime.

Compact terahertz multiheterodyne dual-comb spectroscopy based on self-detection quantum cascade lasers

ABSTRACT. We demonstrate the most compact terahertz multiheterodyne dual-comb spectroscopy using two quantum cascade lasers (QCLs) without a need of additional fast detectors. To prove the spectroscopic ability, we further show that the compact dual-comb system can be used to calibrate the relative humidity in the air and fast identify gases in the enviornment. Due to the small optical coupling aperture (150 μm), it is also potential to use the dual-comb technique for terahertz imaging.

15:00-19:00 Free Time

Free time to enjoy the resort's pools, golf, and other amenities - or just to explore the local area.

19:00-20:30 Session 5: 2D Materials
Terahertz High Harmonic Generation in Dirac Materials (Invited)

ABSTRACT. We describe the experimental techniques, approaches, as well as results of recent measurements on nonlinear optical conversion using  different types of Dirac materials. For example, highly efficient THz harmonics generation up to the 7th order in a single layer graphene sample at ambient conditions has been demonstrated utilizing THz pulses with rather moderate electric field strength of only few 10 kV/cm.

Tunable gated graphene-on-polyimide Terahertz Modulators

ABSTRACT. We present graphene-on-polymide Terahertz frequency modulators, in which the optical power is modulated by the gate-controlled optical conductivity of a single layer graphene, placed on a double-metal polyimide waveguide. With the introduction of a suitable grating coupler, the modulator bandwidth can be tuned beyond the nl/4 mode. We demonstrate a gate-tuned reflectance modulation higher than 25%, with a tunable by design modulation peak of 90% at fixed frequencies in the 1.85-2.3 TH range.

Infrared and terahertz optics and plasmonics of Weyl semimetals
PRESENTER: Alexey Belyanin

ABSTRACT. Weyl fermions were recently shown to exist in the nonrelativistic condensed-matter setting as gapless quasiparticle states in topological metals. We calculate their bulk and surface conductivity tensors and determine the peculiar properties of both bulk and surface electromagnetic eigenmodes. We show how optical spectroscopy can be used to study topological properties of electron states. Moreover, unusual optical properties of these materials can be utilized in future optoelectronic devices.

Fundamental limits to graphene plasmonics in hBN heterostructures (Invited)

ABSTRACT. Enabled by cryogenic “scanning plasmon interferometry”, we resolve the effect of phonon scattering and dielectric loss on graphene plasmons, thereby revealing fundamental limits for plasmon propagation at T<70K. Moreover, by directly resolving the enhanced propagation of hyperbolic phonon polaritons in isotopically pure boron nitride as a function of temperature, we can forecast the ultimate performance of hBN-encapsulated graphene for mid-infrared plasmonics at cryogenic temperatures.