the branch of photometry that deals with the study of pulsed radiation fluxes and the evaluation of the parameters of such fluxes in time intervals that are shorter than the pulse recurrence times.
The recent development of pulse photometry began in the 1950’s and 1960’s and is associated with the use of flash lamps and lasers. The early development was based on studies of flashing lights by the French scientists A. Blondel and J. Rey in the late 19th and early 20th centuries as well as on research in the 1920’s and 1930’s that has been summarized by the French photometrician M. Moreau-Aneux.
Pulse photometry includes the calculation and measurement of the spatial, temporal, spectral, and energy characteristics of pulsed radiation sources; the theoretical basis of the methods used; the computation of errors of measurement; and the metro-logical provision of units of measurement. In pulse photometry, the system of photometric quantities is supplemented by integrals over time of radiometric quantities and of “visual” photometric quantities, such as luminous pulse emittance, exposure, and luminance; the integrals characterize the energy of the radiation pulses. Quantities or parameters used in pulse-measurement technology also supplement the photometric quantities.
The flux density of radiation from pulsed sources, especially for nanosecond and picosecond (10–9–10–12) pulse lengths, often reaches values at which certain laws of classical photometry are violated. The classical laws hold unconditionally when the transfer function of an optical material or radiation detector is invariable. The transfer function characterizes a number of important properties of optical media and optical detectors when such a medium or detector is exposed to radiation pulses or to any radiation that varies in time. Examples of properties characterized by the transfer function include the transmission factor of a specimen of an optical medium and the spectral sensitivity of a light detector at a specified moment in time.
For pulse photometry, the evolution of laser technology has necessitated the development of new measurement methods, such as the detection of light pulses by nonlinear crystals (seeNONLINEAR OPTICS); the automatic processing of results obtained by measurements; and the construction of radiation detectors with a high time resolution and a wide range over which the detector’s response to variations in the incident radiation flux is linear.
Pulse methods of radiation measurement provide a high accuracy and high sensitivity. Such methods are also used to determine the photometric properties of bodies, such as the transmission factor and reflection coefficient. The methods are very promising in connection with the use of digital computer technology in photometers. The speed of operation of digital computers is compatible with the pulse lengths of most radiation sources, so that the information may be processed in real time.
REFERENCESVol’kenshtein, A. A., and E. V. Kuvaldin. Fotoelektricheskaia impul’snaia fotometriia. Leningrad, 1975.
E. V. KUVALDIN