Spectral measurement system built by a lock-in amplifier and a chopper, only measures the light intensity with a modulated frequency, so as to avoid the influence of other external noise, which can achieve the detection of low light with high precision.

Diagram of spectral measurement  (F: SSI OE3001optical chopper   G: grating spectrometer  B: photoelectric probe 

D: praseodymium rubidium glass samples  C: sample box  E: bromine tungsten light source  H: computer)

The light from the bromine tungsten lamp modulated by optical chopper OE3001 becomes a light with certain frequency information. Then it becomes monochromatic light after passing through the grating spectrometer.  Depending on the structure of the sample, it will absorbs the light of a particular wavelength when the monochromatic light hits the sample. Then the light converts to an electric siganl when shines on probe B. At last, the lock-in amplifier will detect this weak electric signal.