Mark E. Barnes

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.

Terahertz emission by diffusion of carriers and metal-mask dipole inhibition of radiation

Terahertz (THz) radiation can be generated by ultrafast photo-excitation of carriers in a semiconductor partly masked by a gold surface. A simulation of the effect taking into account the diffusion of carriers and the electric field shows that the total net current is approximately zero and cannot account for the THz radiation. Finite element modelling and analytic calculations indicate that the THz emission arises because the metal inhibits the radiation from part of the dipole population, thus creating an asymmetry and therefore a net current. Experimental investigations confirm the simulations and show that metal-mask dipole inhibition can be used to create THz emitters.

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.

Simulation of metallic nanostructures for emission of THz radiation using the lateral photo-Dember effect

A 2D simulation for the lateral photo-Dember effect is used to calculate the THz emission of metallic nanostructures due to diffusion currents in order to realize a series of THz emitters.

Gain saturation in 60-fs mode-locked semiconductor laser

A passively mode-locked optically-pumped InGaAs/GaAs quantum well laser with an intracavity semiconductor saturable absorber mirror emits sub-100-fs pulses. Pulse energy declines steeply as pulse duration is reduced below 100 fs due to gain saturation.