This high-precision spectrometer is used to examine the fine structure of the spectral characteristics of continuous-wave lasers. The spectrometer is based on a confocal Fabry-Perot (F-P) cavity, which contains two high-reflectivity mirrors. By using a piezoelectric transducer to change the spacing between the mirrors, the cavity can act as an extremely narrow bandpass filter. After measuring the free spectral range (FSR) of the confocal cavity, the time base of an oscilloscope can be calibrated to enable quantitative measurement of the laser line shape. According to the design of the confocal cavity, the distance d between the mirrors is equal to the radius R, allowing the laser beam to be easily aligned. This series of models is compatible with Thorlabs Piezo drivers.

Response Time

Transmitted PD signal using 780nm laser sweep. Note that no careful mode matching was performed, so the peak spacing is about 1.5GHz.

The peak a was fitted and the peak position and width were found to be 0.059 and 0.147 respectively.

The peak b was fitted and the peak position and width were 28.97 and 0.134 respectively.

The overall result shows that the fineness at 1063nm is about 205.8 and the resolution is 1500/205.8~7.3 MHz.