GaN laser diodes have the potential to be a key enabler for many quantum technologies, including quantum sensing, precision metrology, quantum communications and quantum computing, since the AlGaInN material system allows for laser diodes to be fabricated over a wide range of wavelengths from ultra-violet to visible. Furthermore, GaN allows the development of very high specification laser diode sources that are portable, robust and provide practical solutions that are otherwise unobtainable using more conventional laser sources. Novel applications for quantum technologies include GaN laser sources for cold-atom interferometry, such as next generation optical atomic clocks, quantum sensors and quantum metrology. Several approaches are taken to achieve the required linewidth, wavelength and power for cold-atom interferometry, including an extended cavity GaN laser diode (ECLD) system, and a distributed feedback ( DFB) GaN laser diode with side- wall etched nano-gratings. We report the development of a generic passive waveguide photonic integrated circuit (PICs) platform for quantum applications that covers all the key cold-atom wavelengths for quantum sensing, including the 369nm cooling transition for Yb+, 422nm for Sr + and 461nm for Sr neutral.

Miniaturization of laser sources is crucial to the translation of quantum technologies from the laboratory to the real world. Typically, the lasers required for cooling and trapping of atoms and ions make up a significant footprint of the measurement system. Increasing robustness and reliability whilst removing noise sources is a key challenge whilst reducing volume. Direct generation GaN based external cavity diode lasers offer lower SWaP-C compared to traditional frequency doubled alternatives. Butterfly packaged single frequency sources operation in the blue-UV allow numerous atomic transitions including Sr, Sr+, Yb, Yb+, Mg and Ca to be targeted.

Standoff scanning dual-comb spectroscopy of explosive materials is demonstrated with quantum cascade lasers at $\sim 8~\mu \text{m}$ . The proof-of-concept of the spectrometer, capable of the detection and identification of explosive materials at a distance of 3 m, has a detection limit of cyclotrimethylenetrinitramine (RDX) and pentaerythritol tetranitrate (PETN) on various surfaces of 5– $8~\mu \text{g}$ /cm2 in a scanning regime and 2– $3~\mu \text{g}$ /cm2 with stationary beam in reflection–absorption and backscattering modes.

A proof-of-concept of a scanning stand-off dual-comb spectrometer for explosives detection and identification at 3 m distance is demonstrated. Detection of two types of explosives: RDX and PETN on various surfaces was carried out in reflection-absorption and backscattering modes. A scanning area of 18 cm X 18 cm (400 pixels) was covered in ~2.5 sec. Identification method was based on Pearson’s correlation coefficients between the recorded reflection-absorption (backscatter reflection) spectra and transmission (reflection) FTIR of substances, with baseline subtraction using the asymmetric least square smoothing algorithm. Detection limits of the laboratory system of < 2 ug/cm2 were achieved.

The identification of explosives residue and other harmful materials in field is a key problem to solve for world safety. Here we present a point-by-point imaging technique based on stand-off dual-comb spectroscopy carried out with QCL frequency combs using a fast scanning technique to provide hyperspectral images with species specific absorption spectra.

Quantum based devices offer distinct advantages over conventional technology, such as improved sensitivity for sensing applications or enhanced accuracy for metrology. To utilize this potential, a number of technical requirements must be met, such as the cooling and trapping of neutral atoms for their use as quantum systems. We present our work on InGaN-based semiconductor cooling lasers for a variety of atomic species such as strontium, magnesium and ytterbium whos target wavelength was met by quantum-well composition engineering. Results on growth-epitaxy, facet coating as well as different configurations such as ECDL and MOPAs are presented, depending on the requirement of the application.

Systems with the ability to observe and manipulate individual quantum states have been brought to applications that include among others satellite-free navigation and high-precision gravimetric sensing. Fundamentally, the applicability of quantum technology is limited by the complexity and financial burden of light sources required for such systems. These sources need to feature high optical power combined with compromised beam quality and frequency-stabilized narrow-linewidths. These parameters directly influence the performance of the quantum technology measurement system. Semiconductor devices are able to provide high brightness over broad spectral regions through band-gap engineering. InGaN-based laser sources can be engineered to operate from 380nm to 530 nm. This aligns well with the transitions of atomic species such as strontium, magnesium and ytterbium. However, a challenge remains to offer the narrow-linewidths (<1 MHz) and the high powers (>100 mW) required for many of these applications. We will present our development of GaN based narrow-linewidth seed and tapered amplifiers to operate at 461nm for first stage strontium cooling. This includes growth of custom optimised GaN epitaxy for operation at 461 nm, a robust ECDL geometry, a novel tapered amplifier design and important work in characterising and minimising the surface reflectivity to identify suitable working parameters. A comprehensive characterization of the device will be presented.

consumption and financial burden of the multiple light sources required for such systems. The AlGaInN material system allows for single transverse mode laser diodes to be fabricated with optical powers up to 100 mW over a wide range from ~380 nm up to ~530 nm. By tuning the indium content and thickness of the GaInN quantum well, we have developed a range of AlGaInN diode-lasers targeted to meet the wavelength and power requirements suitable for optical clocks and atom interferometry systems. One of the major limiting factors in nitride laser diode development has been the lack of a suitable low defectivity and uniform GaN substrate. Recently, single crystal growth of large area, very low dislocation-density and uniform GaN substrates are grown using a combination of high temperature and high pressure enabling a range of AlGaInN laser technology to be developed. This direct light generation at the required wavelength is crucial to reduce complexity and size of the overall system, and to ensure a high wall-plug efficiency that is critical for space and mobile applications. We will present our development of GaN based, low SWaP, frequency-stabilised external-cavity seed and tapered amplifiers to operate at 461nm for first stage strontium cooling. This includes growth of custom optimised GaN epitaxy for operation at 461 nm, a robust ECDL geometry, a novel tapered amplifier design and important work in characterising the optical performance and minimising surface reflectivity to identify suitable working parameters.

Here we report our recent achievements towards a compact, portable, handheld device for contactless real-time detection and identification of explosives and hazardous substances via reflectance spectroscopy in the 7.5 mu m - 10 mu m spectral region. The mid-IR spectroscopic measurement principle relies on selective illumination of the target using broadly tunable external cavity quantum cascade lasers (EC-QCLs). A resonant micro-opto-electro-mechanical systems (MOEMS) grating enables fast wavelength tuning in the external cavity, allowing the full spectral scan to be completed in < 1 ms. The diffusely backscattered light's intensity dependence on illumination wavelength provides spectroscopic information to identify threat compounds via our spectral database, containing a large number of materials relevant in a security context. We present a handheld portable, albeit tethered, device capable of real-time identification of hazardous substances at a range of 1 m. We will outline future improvements to increase the system's usability, such as integrated computing power, automated focusing to that allow use over a range of detection distances and spatial scanning for background subtraction.

We present results from our recent development of a multi-beam Doppler lidar system for accurate 3-dimensional wind measurements. The eye-safe all-fibre system consists of a single seed laser that is amplified in multiple stages and shared between the three emitters. Steps towards wind turbine blade integration will be outlined.

Abstract. We report on mid-IR spectroscopic measurements performed with rapidly tunable external cavity quantum cascade lasers (EC-QCLs). Fast wavelength tuning in the external cavity is realized by a microoptoelectromechanical systems (MOEMS) grating oscillating at a resonance frequency of about 1 kHz with a deflection amplitude of up to 10 deg. The entire spectral range of the broadband QCL can therefore be covered in just 500  μs, paving the way for real-time spectroscopy in the mid-IR region. In addition to its use in spectroscopic measurements conducted in backscattering and transmission geometry, the MOEMS-based laser source is characterized regarding pulse intensity noise, wavelength reproducibility, and spectral resolution.