Cavity ring-down spectroscopy technology is a emerging method of spectrum detection. The technology is especially suitable for trace absorption of substance with its characteristics of long absorption optical path and unaffected by the change of light intensity. It is applied to the accurate measurement of high reflectivity of lens (accuracy up to 10-4 ～10-6) and trace gas detection because of simple device and easy quantitative measurement.

    As shown in the fig 1, optical resonant cavity composed of high reflectivity lens M1 and M2, when the 532nm pulsed laser along the optical axis is injected into the cavity, the laser pulse is reflected back and fourth between the two mirrors and from oscillation. Ring-down process of laser pulse in the cavity is detected by the photodetector behind M2 and ring-down time is recorded. Then the reflectivity of lens can be calculated out according to the ring-down time. The students can learn the method to measure the reflectivity of lens accurately by the experiment.

Name

Specifications

Laser

Q-switched laser, Wavelength:532nm（Include current source）

Plane-concave lens

R=600mm, concavity: high-reflectivity film of 1064nm (different radius of curvature, different transmittance, selectable)

Photodetector

Detection wavelength coverage: 200-1100nm, Rise time:1ns

Others

Slideway, adjusting bracket, Iaser goggle, baffle, etc.