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Two instruments which make use of the properties of gas laser beams are described. In the velocity meter the laser provides intense illumination at two lines separated by a known distance. Dust particles crossing these lines scatter light, and the time interval between the two pulses of scattered light gives the particle velocity. The meter is simple and accurate and the method avoids the need to insert probes into the flow. In the deflection meter, the laser beam after passing through the object is detected by opposed photocells whose output is thus a measure of the beam deflection. The device is extremely sensilive, and possible applications include deteclion or measurement of temperature or concentration gradients, boundary layer profile measurements and turbulance detection.