The important developments in the field of infrared measurements are traced from 1800 to the present time. Four periods are considered and it is shown that the developments of the last period (1945 to the present time) were brought about by researches which had been carried out previously. The improvements of sources, detectors, optical materials, and electronic amplifiers are discussed.
Infrared measurements have been made for the last one hundred and fifty years, but this field of investigation is still very active with about 600 papers appearing in the scientific journals each year. Infrared measurements are a very valuable tool for the investigation of many problems. While the greatest interest is in the field of chemistry in the analysis of compounds and the determination of molecular structure, many fields, such as physics, geology, biology, and astrophysics, have problems which can be solved by infrared techniques. This discussion will be concerned primarily with the improvements and developments in methods of measurement of infrared radiation, rather than the applications.
The one hundred and fifty years of infrared research may be divided generally into four periods: (1) from the beginning, with the discovery of infrared energy by Herschel, in 1800, to the development of the infrared spectrometer by Pringsheim in 1883 ; (2) the period from 1883 to 1917 which produced great strides in the qualitative and quantitative analysis of materials; (3) the period from 1917 to 1940 which was characterized by many theoretical advances (it was during this period that the grating spectrometer was first utilized for the measurement of molecular rotation-vibration bands); and (4) the period extending from 1940 to the present time which has seen the development of new prism materials such as CsBr and CsI, which has extended prism measurement out to 50/z, the introduction of radiation detectors such as PbS, PbSe, and PbTe, which have sensitivities up to 1000 times that of the thennocouple, and the building of spectrometers of high resolving power through the use of precision optics.
After the discovery by Herschel of infrared radiation by the rise in the temperature of thermometers, the next development was the