Abstract
Recently, semiconductor light-emission devices, tunable-diode lasers (TDLs) and light-emission diodes (LEDs), have begun being used as light sources for infrared absorption hygrometers. In order to use these semiconductor light emission devices for a two-wavelength infrared absorption hygrometer to measure the humidity inside a cloud chamber containing ice particles and aerosols, two light beams emitted from two devices must be combined into one beam so that the hygrometer measures the same measuring volume with two wavelengths. Incandescent light has a very wide wavelength band including two wavelengths that can be used for infrared absorption hygrometers.
We decided to develop an infrared absorption hygrometer to measure the humidity inside a cloud chamber containing ice particles and aerosols using an incandescent light source and subsequently fabricated a prototype hygrometer to measure humidity at normal temperature and ordinary pressure. This prototype hygrometer has an optical beam splitter and two optical filters to measure two wavelength bands of infrared, the water vapor absorption band at 1.9μm and a nonabsorption band at 1.6μm. The prototype needs no rotating filter motor that may cause mechanical vibration, and it has variable measuring path lengths up to several meters. The calibration data demonstrate that the hygrometer has a measurement accuracy within ±5% for relative humidity when the temperature varies within two degrees. In the future, we will improve the accuracy and stability for measuring humidity and examine how to install the hygrometer in the cloud chamber.
