Optical Method for Absolute Velocity Calibration of Mössbauer Spectrometers

The variable ``moiré pattern,'' formed when a 1:1 image of an 8 μ grating connected to a Mössbauer drive is reflected back onto itself, is utilized to measure the instantaneous velocity of the drive. A photodiode converts the intensity modulated light from the pattern into an electrical signal. From this signal pulses are derived that correspond to shifts of the grating by multiples of 2 μ. These pulses can be applied to a multichannel analyzer used as a part of the Mössbauer spectrometer and thus yield a velocity calibration spectrum. Instantaneous velocities can be measured with accuracies down to about 1 μ/sec.