We report the characterization of a set of broad-area semiconductor diode lasers with mid-wave infrared (3–5 μm) emission wavelengths. The active region of each laser structure is a 5- or 6-period multiple quantum well (MQW) with Ga0.75In0.25As0.22Sb0.78 barriers and type-II (broken-gap) Ga0.75In0.25Sb/InAs superlattice wells. The cladding layers of each laser structure are n- and p-type InAs/AlSb (24 Å /24 Å) superlattices grown lattice-matched to a GaSb substrate. By tailoring constituent layer thicknesses in the Ga0.75In0.25Sb/InAs superlattice wells, laser emission wavelengths ranging from 3.28 μm (maximum operating temperature=170 K) to 3.90 μm (maximum operating temperature=84 K) are obtained.

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Molybdenum-doped barium titanate crystals have been grown and characterized. Electron paramagnetic resonance spectroscopy has confirmed the presence of Mo5+ centers in reduced crystals that correlate with a strong optical absorption band at ∼600 nm. Self-pumped phase-conjugation and electro-optic beam-coupling measurements indicate that the reduced crystals are photorefractive in the visible, as well as the near-infrared wavelength region.

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Spin-exchange optical pumping (SEOP) has 12 been widely used to produce enhancements in nuclear spin 13 polarisation for hyperpolarised noble gases. However, some 14 key fundamental physical processes underlying SEOP 15 remain poorly understood, particularly in regards to how 16 pump laser energy absorbed during SEOP is thermalised, 17 distributed, and dissipated. This study uses in situ ultra-low 18 frequency Raman spectroscopy to probe rotational temper-19 atures of nitrogen buffer gas during optical pumping under 20 conditions of high resonant laser flux and binary Xe/N 2 gas 21 mixtures. We compare two methods of collecting the Raman 22 scattering signal from the SEOP cell: a conventional 23 orthogonal arrangement combining intrinsic spatial filtering 24 with the utilisation of the internal baffles of the Raman 25 spectrometer, eliminating probe laser light and Rayleigh 26 scattering, versus a new in-line modular design that uses 27 ultra-narrowband notch filters to remove such unwanted 28 contributions. We report a *23-fold improvement in detection sensitivity using the in-line module, which leads to faster data acquisition and more accurate real-time monitoring of energy transport processes during optical pumping. The utility of this approach is demonstrated via measurements of the local internal gas temperature (which can greatly exceed the externally measured temperature) as a function of incident laser power and position within the cell.