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Measurement of the laser beam propagation factor M 2 is essential in many laser applications including materials processing, laser therapy, and lithography. In this paper we describe the characterisation of a prototype device using a cross-distorted diffraction grating known as an Image Multiplex (IMP (R) ) grating, to measure the M 2 value of laser beams. The advantage of the IMP (R) grating instrument lies in its ability to simultaneously image nine positions along the beam path. This enables beam propagation parameters to be calculated both for pulsed lasers and lasers with rapidly changing propagation characteristics. This is in contrast to the scanned technique recommended by the ISO, which is relatively slow and in practice can only be easily used with cw sources. The characterisation was accomplished by comparison of results from the IMP (R) grating device with those obtained using the accepted methodology described in the ISO 11146 series of standards through measurements conducted by the National Physical Laboratory. The scope of the work also included provision of a traceability route to international standards, and an uncertainty budget, to allow the intended user community to have confidence in measurements obtained when using the device, and to enable them to use it as part of their quality framework.

Non-linear optical wavelength conversion of near-infrared lasers within optical parametric oscillators (OPOs) offers a route to powerful tunable sources in the mid-infrared (mid-IR). Engineered quasi-phasematched (QPM) non-linear optical materials based on gallium arsenide (GaAs) offer an alternative to conventional birefringently phasematched single-crystal materials such as ZnGeP 2 , which are currently used in mid-IR OPOs. QPM GaAs crystals have been assembled from commercially available, high-optical quality 100-micron thickness gallium arsenide (GaAs) wafers using a novel glass-bonding (GB) process. This uses thin layers of an infrared transmitting glass (refractive index matched to GaAs) deposited onto each GaAs wafer, which, when heated under pressure, fuse the wafers together to form a monolithic structure. By varying the thickness of the deposited glass layers, the dispersion in the glass can be used to compensate for variations in GaAs wafer thickness and to fine tune the phasematching wavelengths of the QPM crystal. GBGaAs crystals with up to 100 layers have been designed and built for wavelength conversion from 2 mm into the mid-IR. We report the performance of these crystals used as optical parametric amplifiers (OPAs) in the mid-IR, when pumped by a 2.094 mm source, and compare these results to measurements for a ZGP OPA. In addition, the dependence of conversion within GBGaAs crystals on the polarisation state of the amplifier seed beam has been investigated along with the temperature dependence of the optimum operating wavelength. Good agreement between experimental results and performance predictions obtained from a numerical model is observed.

We describe a compact laser beam profiler that records multiple images of a laser beam at different positions along the beam waist in a single shot. This is used to determine the laser beam parameter M2. It is known that if light is incident on a curved grating such as a section of a Fresnel zone plate, then the +1 and -1 diffracted orders are focused or defocused. By combining two curved gratings and a conventional lens, it is possible to build a system in which a mosaic of nine images are created, corresponding to nine separate object planes. These nine images can be processed and fitted to an appropriate beam profile. This type of system measures beam quality in real time without any moving parts, and has the potential to provide real time monitoring of pulsed lasers, lasers with dynamic spatial behaviour, and in systems where beam handling optics may produce transient aberrations. Unlike other 'single shot' techniques, this technique makes no assumptions about beam propagation, and produces a value of M2 based only on measurements of beam waists.

We describe a novel wave-front sensor comprising a distorted diffraction grating, simple optics, and a single camera. A noniterative phase-diversity algorithm is used for wave-front reconstruction. The sensor concept and practical implementation are described in detail, and performance is validated against different Zernike modes and a representative atmospheric phase map.