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.

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.Comment: 4 pages, 6 figure

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.

We report high qubit coherence as well as low cross-talk and single-qubit gate errors in a superconducting circuit architecture that promises to be tileable to two-dimensional (2D) lattices of qubits. The architecture integrates an inductively shunted cavity enclosure into a design featuring nongalvanic out-of-plane control wiring and qubits and resonators fabricated on opposing sides of a substrate. The proof-of-principle device features four uncoupled transmon qubits and exhibits average energy relaxation times T 1 = 149(38) μs, pure echoed dephasing times T ϕ, e = 189(34) μs, and single-qubit gate fidelities F = 99.982(4)% as measured by simultaneous randomized benchmarking. The 3D integrated nature of the control wiring means that qubits will remain addressable as the architecture is tiled to form larger qubit lattices. Band structure simulations are used to predict that the tiled enclosure will still provide a clean electromagnetic environment to enclosed qubits at arbitrary scale.

We present the first demonstration of integrated waveguides in planar silica devices fabricated using direct UV writing with 213 nm laser light. Waveguides were produced with different writing fluences and the NA and MFD of each were measured. Single mode waveguides were achieved at fluence values one tenth that typically required when operating with a 244 nm laser, allowing for more rapid fabrication. A maximum in-plane index change of 2.4 x10 −3 for a writing fluence of 5 kJ cm −2 was estimated from NA measurements. Finally cutback measurements were performed and a propagation loss of 0.42 ± 0.07 dB cm −1 was directly measured, though losses as low as 0.2 ± 0.03 dB cm −1 are indicated through calculations.

We demonstrate thermal classification of sequentially written fiber Bragg gratings. This Letter presents a process to determine the type of fiber Bragg grating written in SMF28 and GF4A by introducing the gratings to thermal treatment. This technique can be applied to several approaches based on sequential writing, including the small spot direct ultraviolet writing technique. Four different types of gratings have been identified, which are dependent on the fiber type and fluence used during the writing process.

Multiplexed gallium-arsenide (GaAs)-based terahertz (THz) emitters fabricated with periodic double-metal structures are demonstrated and the effect of different metals on the THz output is investigated. THz emission originates from the lateral photo-Dember effect and from the different Schottky barrier heights of the chosen metal pair. The metal combinations used were Au-Al, Au-Pb and Cu-Cr. The emitters were characterised according to temperature and the highest peak-to-peak THz emission was achieved with the Cu-Cr metal pairing at 150 K.Introduction: Lateral photo-Dember (LPD) emitters have been demonstrated to be robust terahertz (THz) emitters that require no voltage bias to operate [1-3]. An LPD emitter is fabricated by partially masking a semiconductor surface with a deposited metal layer. An ultrafast laser, with above band-gap energy, is focused on the metal-semiconductor boundary. An asymmetrical distribution of photo-generated carriers that are free to diffuse is created near the metal-semiconductor interface. The carriers that diffuse beneath the metal mask form a dipole (dipole B in Fig. 1a), which is quenched due to reflection from the metal surface [4], whereas the carriers that diffuse away from the metal form a dipole (dipole A in Fig. 1a) that is free to radiate and does so parallel to the pump beam.

In this Letter, experimental evidence is provided for an enhanced thermal sensitivity for a double thermal regeneration feature in fiber Bragg gratings fabricated by direct ultraviolet (UV) writing. Here 47 gratings of varying fluence and wavelength were written along a double-clad, germanium-doped core fiber. Subsequently thermal processing without hydrogen loading the fiber was performed and thermal treatment was carried out in a pure oxygen environment. Thermal sensitivity for the double regeneration increased from 13.6±0.3  pm/°C to 21.3±0.2  pm/°C. Furthermore, one of the highest nominal fluence gratings, #45, exhibited a regeneration factor of 1.73.