An optoelectronic system for making quasi-simultaneous recordings of muscle transparency at orthogonal laser beam polarisations

An optoelectronic system is described for making quasi-simultaneous recordings of muscle transparency at orthogonal beam polarisations. A Pockels cell is used to oscillate the E-vector of a laser beam ( lambda =632.8, 514.5, 488 and 457.9 nm) through pi /2 radians (at 7.4 kHz), between 0 degrees and 90 degrees relative to the muscle long axis. The intensity of light transmitted by the muscle is detected using a photomultiplier tube. The photomultiplier output is fed to a sample-hold device which generates two analogue signals, each of which records the transmitted intensity at one of the two incident E-vector orientations. The data are captured using a dual-channel transient recorder and are stored on floppy discs. The ability of the system to make time-resolved (millisecond scale) measurements of muscle conservative dichroism is illustrated with recordings made during 'ramp' stretches applied to fully activated frog muscles.