[20p-E205-1~12] 3.8 Optical measurement, instrumentation, and sensor

[20p-E205-2] Phase Noise Reduction with Low Impedance Reception of Optical Current in Probe- Light-Noise Cancelling with Pulse-Repetition-Phase Detection Technique

〇Keisuke Seto¹, Takayoshi Kobayashi², Eiji Tokunaga¹ (1.Tokyo Univ. Sci., 2.Univ. Electro-Commun.)

Keywords:Noise cancel, pump/probe measurement, spectroscopy

In the pump/probe measurement such as measurement of stimulated Raman scattering, the signal-to-noise ratio (S/N) is limited by the intensity noise of the probe light. We converted the intensity modulation of the probe light due to the sample response to the pump light into the optical pulse repetition phase modulation independently of the intensity noise. Then, we detected the phase of pulse repetition to improve the S/N. However, we found that the junction capacitance of the photodiode fluctuates in response to the light intensity fluctuation and causes phase noise, and the S/N was deteriorated. In this talk, we will present a method to prevent phase noise generation due to junction capacitance fluctuation by receiving photocurrent with a low impedance of the common base or common gate amplifier.