A diffractometer using a lateral effect photodiode for the rapid determination of sarcomere length changes in cross-striated muscle.

A simple method is devised to record rapid sarcomere length changes of muscle fibres using a lateral effect diode. In the standard position the diffractometer records length changes between 1.65 and 3.8 micron, the output being linear 1 V/micron with a frequency response of -3 dB at 1.2 kHz. The absolute error is less than 0.05 micron between 1.65 and 2.80 micron and less than 0.1 micron between 2.81 and 3.30 micron. The resolution of length changes is less than 0.005 micron over the whole range. By varying the detector position the length range can be extended to either side, and spatial resolution can be improved at the expense of length range.