A wide-band polychromator for measurement of shape of electron bunch

We made a 10-channel polychromator with two concave gratings to measure light pulses in the far infrared region. The polychromator covered a wide wavelength range from 0.22 mm to 4.0 mm. An array of ten detectors was mounted on a cold plate of liquid-helium temperature, which was consisted of eight InSb hot-electron bolometers and two magnetically tuned InSb hot-electron bolometers. With the polychromator, we measured the spectrum of the light pulse of coherent radiation emitted from a short-bunch beam of electrons of a linear accelerator, and derived the longitudinal bunch shape within one second. (author)