Application Cases

Experiment Name: Fabry-Perot Cavity Measurement Experiment for Squeezed Light

Test Equipment: Voltage amplifier, Signal generator, Oscilloscope, Laser, Detector, etc.

Experimental Process:

Figure 1: Left: Physical image of the F-P cavity; Right: Structural diagram of the F-P cavity (1. Piezoelectric ceramic, 2. Concave high-reflection mirror for 1064nm wavelength, 3. Bakelite, 4. Red copper, 5. Peltier element, 6. Fine-adjustment screw block, 7. Anti-reflection lens for 1064nm wavelength, 8. Aluminum shell, 9. Invar steel)

In squeezed light experiments, temperature-controlled F-P cavities with high frequency stability are used in multiple setups. The left and right sides of Figure 1 show the physical image and structural diagram of the temperature-controlled F-P cavity, respectively. The temperature controller used in the experiment can output a 3.7V DC signal to control the Peltier element, enabling temperature control of the F-P cavity around 25°C. When the thermistor detects that the temperature inside the F-P cavity is below 25°C, the temperature controller outputs voltage, and the Peltier element begins heating; when the temperature reaches 25°C, the controller stops supplying power, and the Peltier element stops heating. The temperature control range of the F-P cavity is 0-100°C, with a control accuracy of ±0.1°C.

Figure 2: Monitoring optical path diagram of the F-P cavity

Figure 2 shows the monitoring optical path diagram of the F-P cavity. The laser outputs infrared light at 1064nm, which is collimated into approximately parallel light by lens F1, then passes through a beam splitter (composed of H1 and G) and lens F2 before entering the F-P cavity. Photodiode D converts the received optical signal into an electrical signal, which is displayed in real-time on the oscilloscope.

Figure 3: Left: Detector circuit; Right: F-P cavity transmission curve

The circuit connection of the photodiode used in the experiment is shown on the left side of Figure 3. The signal generator produces a 20Hz sawtooth wave signal, amplified by the voltage amplifier to about 180V, driving the piezoelectric ceramic. The right side of Figure 3 shows the F-P cavity transmission peak displayed on the oscilloscope. When external factors affect the output stability of the laser, the transmission spectrum drifts. Therefore, the F-P cavity can be used for real-time monitoring of laser output stability.

Experimental Results:

Figure 4: Transmission spectrum of the resonant cavity

In squeezed light experiments, resonant cavities are used in multiple setups, and the cavity length is adjustable. To check whether the resonant cavity is properly aligned, we estimate its actual finesse. Figure 4 shows the transmission spectrum of one resonant cavity used in the experiment. Diagram (a) shows the transmission spectrum corresponding to the rising voltage of the applied triangular wave signal, while diagram (b) shows the transmission spectrum corresponding to the falling voltage. We simultaneously display the applied triangular wave signal and the transmission signal on the oscilloscope for real-time calculation and adjustment.

Voltage Amplifier Recommendation: ATA-2088

Figure: ATA-2088 High-Voltage Amplifier Specifications

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