Light is a transverse electromagnetic wave, a ray that vibrates in all directions. Its electric field vector E and magnetic field vector H are perpendicular to each other and to the propagation direction of light waves. Because it is mainly the electric field vector that produces the photosensitive effect, the electric field vector is generally considered as the vibration vector of light waves. The plane formed by the electric field vector and the propagation direction of light wave is called the vibration surface of light wave. If the vibration plane does not change with time, this beam of light is called plane polarized light, and its vibration plane is called polarization plane. Plane polarized light can be decomposed into two circularly polarized lights with the same amplitude and frequency and opposite rotation directions. The electric vector rotating clockwise is called right-handed circularly polarized light, and the electric vector rotating counterclockwise is called left-handed circularly polarized light. Two beams of polarized light with the same amplitude and frequency and opposite rotation directions can also be combined into one beam of plane polarized light. If the amplitudes (intensities) of the two polarized beams are different, an elliptically polarized beam will be synthesized. Optical substances have different absorption rates of left-handed and right-handed circularly polarized light, and the difference δδA(Al-Ad) of their light absorption is called circular dichroism (abbreviated as CD). The existence of circular dichroism makes the plane polarized light propagating through this substance become elliptical polarized light, and it can only be observed at the wavelength where absorption occurs. The ellipticity θ of an ellipse is: θ= tg- 1 minor axis/major axis. According to Lambert-Beer law, it can be proved that the ellipticity is approximately θ = θ= 0. 576 lc (εl-εd) = 0。 576 LCδε。 In the δ ε formula, L is the thickness of the medium, C is the concentration of photosensitive substances, and εl and εd are left-handed and right-handed circularly polarized light respectively. Measure the relationship curve between θ (or δ ε) value and wavelength λ at different wavelengths, that is, the circular dichroism spectrum curve. In this spectral curve, if the measured substance has no characteristic absorption, its δ ε value is very small, that is, the characteristic circular dichroism spectrum cannot be obtained. When εl >εd, a positive circular dichroism spectrum curve is obtained, that is, the measured substance is right-handed, if ε l <