Development of a balanced detector with biased synchronous detection and application to near shot noise limited noise cancelling of supercontinuum pulse light

Abstract

We report on the development of a balanced detector suited for multicolor imaging. The source pulsed light is split into probe and reference pulsed light. The reference pulse is delayed through an optical path and the probe and reference pulses are detected by a single photodetector. The signs of the detected signals of the probe and reference pulses are flipped based on a signal synchronous to the light source. Then, the signals are averaged through a low-pass filter. The output signal is proportional to the intensity difference between the probe and the reference. This balanced detector has two features: (1) both the probe and reference pulsed lights are detected by a single photodetector and (2) a voltage bias on the sign flipping compensates for the optical-intensity unbalance between the probe and reference pulsed lights. The first feature enables the probe and reference pulses to travel along a common optical path from a sample through a spectrograph to the photodetector, which minimizes the intensity unbalance between the probe and reference pulses during imaging and spectroscopy. The second feature ensures the complete balanced-detection in whole wavelength range by compensating for the optical unbalance created by deviations in the splitting ratios of the probe and reference lights at different wavelengths. Although a higher signal to noise ratio (SNR) reached to near shot noise limited SNR is attained by attaching a resonator to the photodetector for pulse repetition, the electrical bias cannot compensate for the optical balance. This unbalance is, however, corrected by adjusting the phase of the synchronous signal. We applied the present balanced detection to a stimulated Raman microscope with supercontinuum probe light and demonstrated its noise cancelling performance through capturing polystyrene beads.

Noise cancellation with phase-detection technique for pump-probe measurement and application to stimulated Raman imaging

“…Certain balanced detection methods [26,33,34,35] offer other ways of cancellation of the optical intensity noise on a probe beam. In these methods, a reference beam is prepared from the same beam source as that of the probe beam, and the detected signal of the reference beam is subtracted from that of the probe beam.…”

“…Figure 2 illustrates the optics system for an SRS microscope with phase-sensitive detection. The optics system is similar to that in our previous works [26,33]. A titanium-sapphire laser (Mira 900P, COHERENT) generates the 76.3 MHz optical pulse repetition.…”

“…The input power tends to be more distributed in shorter wavelength components with a PCF of a shorter ZDW at a certain length of the PCF [25]. Hence, a PCF with a ZDW of 790 nm, which is closer to the input wavelength than the 750 nm in the previous work [33], is selected. In addition, the length is increased to 1 m from 30 cm in the previous work [33] to enhance conversion efficiency.…”

“…Hence, a PCF with a ZDW of 790 nm, which is closer to the input wavelength than the 750 nm in the previous work [33], is selected. In addition, the length is increased to 1 m from 30 cm in the previous work [33] to enhance conversion efficiency. The spectral power density is increased by ∼10 times higher than that in the previous work.…”

Flexible digital signal processing architecture for narrowband and spread-spectrum lock-in detection in multiphoton microscopy and time-resolved spectroscopy

“…14 Other approaches forego the lock-in amplifier altogether by placing a resonant LC circuit in the photodiode amplifier, 15 performing collinear balanced detection, 16 or directly digitizing the photodiode signal, performing lock-in demodulation and further postprocessing in software. 17 In this work, we have replaced the lock-in amplifier with a high-speed data acquisition board, performing all signal processing in the coprocessor FPGA.…”