Abstract: A single-frequency laser apparatus comprises a mirror and a volume Bragg grating (VBG) reflector defining a laser cavity therebetween and an optical gain material for emitting and amplifying an intra-cavity beam in the laser cavity. The optical gain material comprises a transition-metal doped crystal such as a crystal doped with transition-metal ions selected from one or more of Ti3+ ions, Cr2+ ions, Cr3+ ions or Cr4+ ions. A reflectivity spectrum of the VBG reflector and an optical length of the laser cavity are selected so that a beam output from the laser cavity is a single-frequency output beam and/or includes only one longitudinal mode of the laser cavity. The laser apparatus may provide a robust, compact, low cost, high-power wavelength adjustable (from approximately 650 to 950 nm), narrow linewidth (<100 kHz), single frequency laser source which is suitable for a wide range of applications from laser sensing, spectroscopy, and high precision frequency metrology sectors.

Abstract: A detector comprises an optical parametric oscillator having a non-linear material adapted to convert via a parametric process pump light into down converted light of two different wavelengths, the first wavelength being longer than the second wavelength. The non-linear material is provided in a down converted wave cavity arranged to resonate only one of the first or second wavelengths. The detector comprises means for modulating light in the down converted wave cavity to induce an acoustic or pressure wave caused by absorption of the resonant one of the first and second wavelengths. The detector further comprises means located in the down-converted wave cavity for detecting the acoustic or pressure wave. The detector may be used for detecting or sensing very low levels of a fluid, for example a gas such as ethane.

Abstract: A detector comprises an optical parametric oscillator having a non-linear material adapted to convert via a parametric process pump light into down converted light of two different wavelengths, the first wavelength being longer than the second wavelength. The non-linear material is provided in a down converted wave cavity arranged to resonate only one of the first or second wavelengths. The detector comprises means for modulating light in the down converted wave cavity to induce an acoustic or pressure wave caused by absorption of the resonant one of the first and second wavelengths. The detector further comprises means located in the down-converted wave cavity for detecting the acoustic or pressure wave. The detector may be used for detecting or sensing very low levels of a fluid, for example a gas such as ethane.

Abstract: An optical parametric oscillator comprising: an optical cavity; a semiconductor gain-medium located within the optical cavity, such that together they form a semiconductor laser, and a nonlinear material located within the cavity such that the nonlinear material continuously generates down-converted idler- and signal-waves in response to a pump-wave continuously generated by the semiconductor gain-medium, wherein the pump wave is resonant within the optical cavity and one or other but not both of the down-converted waves is resonant within the pump wave cavity or a further optical cavity. Brewster plates ensure singly resonant optical parametric oscillators and a birefringent filer is used for frequency setting. Coupled cavities allow for setting the photon lifetime in the cavity that relaxation oscillations are prevented.

Abstract: An optical parametric oscillator comprising: an optical cavity; a semiconductor gain-medium located within the optical cavity, such that together they form a semiconductor laser, and a nonlinear material located within the cavity such that the nonlinear material continuously generates down-converted idler- and signal-waves in response to a pump-wave continuously generated by the semiconductor gain-medium, wherein the pump wave is resonant within the optical cavity and one or other but not both of the down-converted waves is resonant within the pump wave cavity or a further optical cavity. Brewster plates ensure singly resonant optical parametric oscillators and a birefringent filer is used for frequency setting. Coupled cavities allow for setting the photon lifetime in the cavity that relaxation oscillations are prevented.

Abstract: A back scatter absorption detector/imager having an optical parametric device for generating sensing radiation, the optical parametric device having a nonlinear medium (NLC) and a pump wave laser source, the nonlinear medium (NLC) being able to generate a signal and an idler wave in response to being stimulated with the pump wave, thereby to generate sensing radiation, and a detector (D) for detecting any sensing radiation back-scattered from a target area, characterized in that the pump wave laser source and the nonlinear medium (NLC) are provided in the same optical cavity.

Abstract: A back scatter absorption detector/imager having an optical parametric device for generating sensing radiation, the optical parametric device having a nonlinear medium (NLC) and a pump wave laser source, the nonlinear medium (NLC) being able to generate a signal and an idler wave in response to being stimulated with the pump wave, thereby to generate sensing radiation, and a detector (D) for detecting any sensing radiation back-scattered from a target area, characterised in that the pump wave laser source and the nonlinear medium (NLC) are provided in the same optical cavity.