Etalon Characterization

To evaluate the produced etalon, use the fiber optic setup and a measurement system capable of temperature-tuning the laser step-wise with a sufficient data-logging rate. To obtain measurements for calculating the theoretical free spectral range or FSR, perform a temperature sweep corresponding to at least two FSRs by increasing the temperature step-wise and letting the thermoelectric cooler settle for two to three seconds before measuring for another two to three seconds each time. After performing a temperature sweep corresponding to a wavelength sweep of the laser, process the measurement data with any numerical calculation program.

Use any signal processing library with an integrated peak finder. The distance between two subsequent peaks represents FSR. Evaluate the width of the peak at its half height to calculate the full width at half maximum.

Convert the temperature into wavelength by using the temperature-tuning coefficient of the laser. Calculate the full width at half maximum and FSR from the measurements. Finally, calculate the finesse of the fabricated Fabry-Perot etalons.

This study resulted in the fabrication of Fabry-Perot etalons with a well-defined reflectance function. A comparison of the measured and calculated metrics of the fabricated Fabry-Perot etalons, etalon demonstrated that the measured finesse and full width at half maximum were comparable to the calculated values of ideal Fabry-Perot etalons. Photothermal interferometry measurements of water vapor and ambient air are shown here.

The signal was extracted by means of a fast Fourier transform and compared to the background signal with the excitation laser turned off.