An Automatic Recording Spectro-radiometer And Its Applications

Abstract

An automatic recording spectro-radiometer has been made for the purpose of accurately and speedily measuring the spectral energy distributions of phosphors, various lamps, and other light sources.The apparatus is composed of a light chopper, monochromator, amplifier and a servo recorder. The light from a cathode luminescence exciting device, C. R. T. screens or other lamps is introduced to this apparatus. A cathode-luminescence exciting device is an inverted T shaped, evacuated demountable glass tube, containing eight pieces of phosphor powder or screen specimen at a time.Either stationary unmodulated C. R. beam excitation or laster excitation is available in this device. The measurements can be made both from the bombarded and unbombarded sides of the screen specimens. The moving of the specimens can be accomplished quite easily in the high vacuum.The light chopper consists of sixteen-blades revolving disc, light choppieg rate being 400 times per second.The monochromator is a constant deviation type of glass prism, and its measurable wave-length range is from 380 miμ to 720 mtμ.For the light receiver, a RCA 1 P 22 photo-electron multiplier tube is used.The amplifier is a 4 stage A. C. amplifier using 6 S J 7 pentodes, and it is tuned sharply at 400 c. p. s. by introduction of a parallel T filter and a tuned output transformer.The servo recorder used is a type in which the revolving direction of the balancing motor is controlled by a relay by which the contact point on the potentio-meter resistor is moved up to the distance proportional to the input signal, and the signal is recorded on the recorder drum with a recording pen fixed on the contact point. For obtaining smooth recording, a small D. C. generator which rotates together with the balancing motor is used to prevent the hunting of the recorder by feeding back its output voltage to the servo input.A mechanical method is used both for making the wave length scale linear and for making the record proportional to the energy at any wave-length of the incoming light. For the former, the rev olving rate of the prism is controlled by using a comparatively large cam. By this means, a precision can be obtained with comparative ease. For the latter, a correction slit is used, whose opening width is accorded with the experimentally determined correction factor for any wave-length This is inserted between the monochromator exit slit and the multiplier phototube hausing and moved along with the variation of wave lengths.The least detectable luminous flux of this apparatus is 10-10 lumen, and the linearity of the feed-back amplifier and the reproducibility are both excellent.For the purpose of showing the performances of this apparatus, comparisions of the recorded curve of a tungsten lamp of 2500°K color temperature with the theoretical one and of the recorded Zrt2 SiO4: Mn phosphor spectrum with the measurement by the photometric method are given. Also as a few examples of the applications of this apparatus, the measurement of the initial decay charaeteristics of maximum spectral energy of phosphors and that of the spectral transmission of tricolor filter for color television, are given.