Alexandrite crystal is commonly used for making alexandrite laser, and it also has a less-known phenomenon called the
alexandrite effect that refers to the color change between different light sources. A novel spectropyrometer for
temperature measurement of a radiating body utilizing the alexandrite effect is introduced. The alexandrite effect method
for temperature measurement is based on the relationship between the temperature of blackbody and the hue-angle in the
CIELAB color space. The alexandrite effect spectropyrometer consists of an optical probe, a spectrometer, a computer,
and an alexandrite filter. It measures the spectral power distribution of a radiating body through the alexandrite filter,
calculates the hue-angle, and determines the temperature. The spectropyrometer is suitable for temperature measurement
of any radiating body with or without spectral lines in its spectral power distribution from 1000 K to 100000 K. The
spectropyrometer is particularly useful for high to ultrahigh temperature measurement of any radiating bodies with
spectral line emissions, such as electric arcs and discharges, plasmas, and high temperature flames.
Some shells from both salt water and fresh water show the phenomenon of iridescence color. Pearls and mother-of-pearls also display this phenomenon. In the past, the cause of the iridescence color was attributed to interference. A scanning electron microscope (SEM) was used to study the surface structure of the shell of the mollusk Pinctada Margaritifera. There is a groove structure of reflection grating on the surface area in where the iridescence color appears. An optic experiment with a laser obtained a diffraction pattern produced by the reflection grating structure of the shell. The study led to a conclusion that the iridescence color of the shell is caused by diffraction. A SEM image of the shells of an abalone Haliotis Rufescens (red abalone) showed a statistically regularly arranged tile structure that serves as a two-dimensional grating. This grating structure causes the iridescence color of the shell of red abalone. The dominant color of the iridescence of shells is caused by the uneven grating efficiency in the visible wavelength range when a shell functions as a reflection grating. The wavelength of the dominant color should be at or near the wavelength of the maximum efficiency of the grating.
The rare earth element neodymium doped yttrium aluminum garnet (Nd:YAG) is a laser crystal widely used for producing laser in the infrared range. Neodymium causes many characteristic absorption peaks in the transmittance spectrum of the Nd:YAG crystal in the visible range. The crystal appears pink under daylight and incandescent light, and colorless under fluorescent light. The colorimetric calculation results of chroma under the CIE standard fluorescent illuminant F7 do not agree with the color appearance under fluorescent light. The calculated chroma values should be near zero to agree with a colorless appearance, but it is actually 11.79 in the CIELAB color space. This failure of the colorimetric calculation is caused by the color matching functions of the CIE colorimetric observers. The color matching functions do not agree with the spectral sensitivity curves of the human eye, especially the x(λ) function does not matches the spectral sensitivity curve of the long wavelength cone photoreceptors.
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