Following its release in the U.S., one instrument after the other was imported to Japan, where they began to be used by major universities, public research institutions, and pharmaceutical and chemical companies. At the same time, research societies and meetings on the subject of infrared spectrometry were inaugurated, leading to an "infrared boom" in Japan. Though Shimadzu also undertook development of its own double beam self-recording infrared spectrophotometer, there were a number of technical issues to be overcome, which prevented us from commercializing it immediately.
The technical issues included the facts that we could not manufacture a large, good quality artificial rock salt crystal and that the sensitivity and responsiveness of the thermocouple we manufactured were insufficient for use as a detector in an infrared spectrophotometer. Manufacture of a large, good quality rock salt crystal was eventually accomplished under the guidance of a professor from a university in Kyoto. We unfortunately remained unable to manufacture a good quality thermocouple, despite considerable trial and error. As a result, we abandoned manufacturing a thermocouple, and decided to use an American made thermocouple.
Development proceeded, now that the necessary parts were no longer an issue. A rock salt prism is deliquescent, which means that if it is left exposed to the highly humid air in Japan, the polished surface will dissolve, becoming rough in texture, and no longer usable. For this reason, a constant-temperature, low-humidity room was prepared for use in equipment manufacture. After considerable effort, the AR-275 double beam self-recording infrared spectrophotometer was completed in 1956. The model number "275" came from the focal length of the collimator mirror in the monochromator.
Globar Light Source
Deliquescence refers to the dissolving of a crystal though the intake of moisture from the air. Deliquescent materials include sodium chloride, potassium bromide, magnesium chloride, etc.
In the figure captioned "Optical System for a Double Beam Self-Recording Infrared Spectrophotometer Using a Rock Salt Prism," this mirror receives the light beam condensed at the slit position, and turns it into a parallel beam. Conversely, it is also used to condense a parallel beam to a single point. It is also referred to as a parabolic mirror.