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

A single-step ductile dicing process capable of manufacturing optical quality facets in lithium niobate (LiNbO 3 ) ridge waveguides with an average surface roughness of 0.29 nm is reported. This result is comparable with surface roughnesses achieved by lapping and polishing and represents an order of magnitude improvement over the prior state of the art in LiNbO 3 waveguide facet dicing.Introduction: Dicing, a form of mechanical sawing, is commonly used in semiconductor and photonics processing to separate individual die from wafers. In most semiconductor processes where functional elements are accessed from the top of the die, dicing speed is more critical than quality and often performed in a 'brittle' regime where cracks and edge chipping on the order of tens of microns are common. In photonics, optical components are more often accessed (launched) from the side of the die and require a surface roughness of a few nanometres to prevent unwanted loss by scatter. Such roughness is typically achieved by laborious extra stages of lapping and polishing, in which individual components are manually handled through multiple mounting and cleaning steps.In recent work, we have demonstrated optical quality dicing of micron-order ridge waveguide structures in germanium telluride with a facet roughness of 3.0 nm (Sa) [1]. Here, we present results in lithium niobate (LiNbO 3 ), a popular nonlinear optical material for use in laser wavelength conversion [2][3][4][5][6]. A single-step ductile dicing process was developed to achieve sub-nanometre surface roughness on periodically poled LiNbO 3 (PPLN) facets, circumventing the need for lapping and polishing. This represents an order of magnitude improvement in surface roughness over previous publications in the field [5].

An external cavity diode laser is demonstrated using a Bragg grating written into a novel integrated optical fiber platform as the external cavity. The cavity is fabricated using flame-hydrolysis deposition to bond a photosensitive fiber to a silica-on-silicon wafer, and a grating written using direct UV-writing. The laser operates on a single mode at the acetylene P13 line (1532.83 nm) with 9 mW output power. The noise properties of the laser are characterized demonstrating low linewidth operation (< 14 kHz) and superior relative intensity noise characteristics when compared to a commercial tunable external cavity diode laser.

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 present a metallic zinc indiffused diced ridge waveguide in magnesium doped periodically poled lithium niobate (MgO:PPLN) capable of generating over 1 W of 780 nm with 70% efficiency. Our 40 mm long waveguide has near circular fundamental mode output with diameter 10.4 µm and insertion loss of -1.17 dB. Using a commercial 2 W EDFA-based system, the SHG output power did not exhibit roll-off at maximum available pump power.

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“Cold atoms” can be used as ultra-sensitive sensors for measuring accelerations and are capable of mapping changes in the strength of gravity across the surface of the Earth. They could offer significant benefits to existing space based gravity sensing capabilities. Gravity sensors in space are already used for many Earth observation applications including monitoring polar ice mass, ocean currents and sea level. Cold atom sensors could enable higher resolution measurements which would allow monitoring of smaller water sources and discovery of new underground natural resources which are currently undetectable. The adoption of cold atom technology is constrained by low technology readiness level (TRL). Teledyne e2v and its partners are addressing this maturity gap through project Cold Atom Space PAyload (CASPA) which is an Innovate UK and Engineering and Physical Sciences Research Council (EPSRC) funded project, involving the University of Birmingham as science lead, XCAM, Clyde Space, Covesion, Gooch & Housego, and the University of Southampton. Through the CASPA project the consortium have built and vibration tested a 6U (approximate dimensions: 100 × 200 × 300 mm) cube Satellite (CubeSat) that is capable of laser cooling atoms down to 100’s of micro kelvin, as a pre-cursor to gravity sensors for future Earth observation missions.