We demonstrate the design and implementation of a fibre-optic beam delivery system for particle image velocimetry applications. The system is designed for the transmission of pulses of high peak power from a Q-switched and frequency-doubled Nd: YAG laer with energies typically in the range of 9 mJ; it is hence suitable for illuminating air flows. Practical laser-induced damage thresholds for large-core stepindex multimode fibres are determined, and through exploitation of inter-modal dispersion in the fibre, intensity variations in the output from the fibre due to laser speckle are suppressed to a visibility of <3.5%. Effective use of the fibre-optic beam delivery system for particle image velocimetry was demonstrated for a turbulent air flow seeded with corn oil droplets of the order of 1-2 pn in diameter; the mean air velocity was 5.5 m s-'.Rolls-Royce pic. 0.355 hm J . ~p p ~.

An electronic speckle pattern interferometer (ESPI) using stroboscopic illumination from a diode laser, and its application in vibration measurement, are described. Diode lasers are readily frequency (FM) and power modulated (AM) via control of their injection current; they are inexpensive and compatible with the single-mode optical fibres used in the described system. However, their modest peak power output demands the use of high-duty-cycle pulses, so that it was necessary to synchronize the illumination with the turning points of the vibration. This was achieved by operating the ESPI system in conjunction with a laser vibrometer. Injection-current-induced FM of diode lasers is non-uniform for modulation frequencies less than about 10 MHz, and to achieve successful stroboscopic illumination an electronic equalization stage was included to shape the current pulse, and hence compensate for the non-uniform FM.

Contrast in an LCoS based projection system is strongly influenced by the on‐ and off‐axis residual device retardance. We describe a general technique to experimentally determine the compensation requirements for reflective modes. This information is applied to the compensator design and the trade‐off between contrast and F/# is explored. The example of normally white 45TN0 mode is given.

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