Paul C. Gow

Investigation of the role of the lateral photo-Dember effect in the generation of terahertz radiation using a metallic mask on a semiconductor.

Pulses of coherent terahertz radiation can be efficiently generated by a lateral diffusion current after ultrafast generation of photo-carriers near a metal interface on the surface of a semiconductor, this is known as the lateral photo-Dember effect. We investigate how the emission depends on the pump spot position, size, power and how it is affected by the application of an applied external bias. We study the role of the metallic mask and how it suppresses emission from the carriers diffusing under it due to a reduction of available radiation states both theoretically and experimentally.

Multiple double-metal bias-free terahertz emitters

We demonstrate multiplexed terahertz emitters that exhibits 2 THz bandwidth that do not require an external bias. The emitters operate under uniform illumination eliminating the need for a micro-lens array and are fabricated with periodic Au and Pb structures on GaAs. Terahertz emission originates from the lateral photo-Dember effect and from the different Schottky barrier heights of the chosen metal pair. We characterize the emitters and determine that most terahertz emission at 300 K is due to band-bending due to the Schottky barrier of the metal.

Fluence and polarisation dependence of GaAs based Lateral Photo-Dember terahertz emitters.

We characterise THz output of lateral photo-Dember (LPD) emitters based on semi-insulating (SI), unannealed and annealed low temperature grown (LTG) GaAs. Saturation of THz pulse power with optical fluence is observed, with unannealed LTG GaAs showing highest saturation fluence at 1.1 ± 0.1 mJ cm(-2). SI-GaAs LPD emitters show a flip in signal polarity with optical fluence that is attributed to THz emission from the metal-semiconductor contact. Variation in optical polarisation affects THz pulse power that is attributed to a local optical excitation near the metal contact.

Multiple lateral photo-Dember terahertz emitters illuminated by a cylindrical micro-lens array

We demonstrate a terahertz multiple emitter design based on the lateral photo-Dember effect and illuminated with a cylindrical micro-lens array. The multiple emitter produces an average of 5.2 times the output power of a single lateral photo-Dember emitter and is capable of reaching bandwidth comparable to that of a single commercial photoconductive antenna.

Mode-locked VECSEL SESAM with intracavity antenna for terahertz emission

Mode-locked Vertical External-Cavity Surface-Emitting Lasers (ML-VECSELs) have seen advances in pulse energy and peak power thanks to improved power handling techniques and structure designs. The significant increase in gain and intra-cavity power, coupled with the VECSELs accessible external-cavity, has made the addition of intra-cavity elements for frequency conversion possible even for lossy conversion mechanisms. In this paper, we report a gold-patterned Semiconductor Saturable Absorbing Mirror (SESAM) that functions both as a slow saturable absorber in a ML-VECSEL and as an intracavity strip line Photo-Conductive Antenna (PCA) for THz emission. Here we describe the design of the strip emitter, THz-Time Domain Spectroscopy (TDS) performed with a ML-Yb fibre laser and the mode-locked characterisation of a ML-VECSEL built with the patterned SESAM.

Leaky mode integrated optical fibre refractometer

A route to monitor external refractive indices greater than the core index of the waveguide is presented. Initial application utilizes an integrated optical fibre (IOF) platform due to its potential for use in harsh environment sensing. IOF is fabricated using a bespoke flame hydrolysis deposition process to fuse an optical fibre to a planar substrate achieving an optical quality, ruggedized glass layer between the fibre and substrate was fabricated. The presented refractometer is created by direct UV writing of multiple fibre Bragg gratings into an etched (22 μm diameter) optical fibre post fabrication. Linear regression analysis is applied to quantify propagation loss by monitoring each FBGs back reflected power. The device operates with a sensitivity of approximately 350 dB/cm/RIU at a refractive index of 1.451 at 1550 nm. Numerical simulations using a transfer matrix method are presented and potential routes for development are discussed.

Taking quantum entanglement out of the lab

The Networked Quantum Information Technologies hub (NQIT) is one of the quantum hubs of the UKs agship scheme, bringing together academia, industry and government. The Optical Engineering and Quantum Pho- tonics group at the University of Southamptons Optoelectronics Research Centre have developed an interactive demonstrator of a key device within NQIT to bring quantum photonics technologies to a wider audience. The system was exhibited at the 2017 UK Quantum Showcase in London to an audience of industry and government. It also featured as part of the Quantum City stand at the 2018 Cheltenham science festival, one of the UKs leading annual science events.

Taking large optical quantum states out of the lab: engaging pupils and the public on quantum photonics sciences

Novel research-inspired outreach activities allow scientists and members of the public to engage in a conversation, increasing the public’s understanding and interest in scientific research. This paper reviews outreach and public engagement initiatives undertaken by researchers from the University of Southampton’s Optical Engineering and Quantum Photonics Group during a 5-year research program grant entitled Building Large Optical Quantum States. The activities have been supported by a UK Engineering and Physical Sciences Research Council program grant and institutional, national and international professional organizations. The paper discusses activities and hand-outs that have been developed to increase the visibility and public understanding of integrated-photonics fabrication and testing facilities, including a cleanroom-based process for the design and fabrication of quantum outreach chips. More than 1,000 of these chips have been distributed to children, parents and government officials in public events and the activities have contributed towards the authors’ research group receiving the 2017 South East England Physics Network Highly Commended Award for Best Research Group. This paper also discusses the impact of these activities and lessons learned.

Dataset for Terahertz focusing and polarization control in large-area bias-free semiconductor emitters

We show that, when large area multiplex terahertz semiconductor emitters that work on diffusion currents and Schottky potentials are illuminated by ultrashort optical pulses, can radiate a directional electromagnetic terahertz pulse which is controlled by the angular spectrum of the incident optical beam. Using the lens that focuses the incident near infrared pulse, we have demonstrated THz emission focusing in free space, at the same point where the optical radiation would focus. We investigated the beam waist and Gouy phase shift of the THz emission as a function of frequency. We also show that the polarization profile of the emitted THz can be tailored by the metallic patterning on the semiconductor, demonstrating radial polarization when a circular emiter design is used. Our techniques can be used for fast THz beam steering and mode control for efficiently coupling to waveguides without the need for THz lenses or parabolic mirrors.

Pressure characterisation Data 180118NB318-2-chip2-27-500um

Dataset supports: Jantzen, A. et al (2018). Pressure Sensing Based on Ratiometric Bragg Grating Loss in a Planar Silica Diaphragm Platform. Advanced Photonics Congress JTu2A.62bg represents the background measurement with reflection from before entering the circuit. loss represents the device response to decreasing pressure.Pressure readings were respectively: 2 24 23.5 23 22.5 22 21.5 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2.5 with an error of 0.25 in Hg. The reading to begin with is the offset value of the gauge.