Computer-based photon-counting lock-in for phase detection at the shot-noise limit

Area of Science:

• Optical Physics
• Instrumentation
• Biophysics

Background:

• Traditional lock-in detection methods are limited by noise sources.
• Photon counting offers high sensitivity but can be challenging to integrate with lock-in principles.
• There is a need for improved signal-to-noise ratio in sensitive optical measurements.

Purpose of the Study:

• To implement a computer-based photon-counting lock-in system.
• To characterize the noise and performance of this novel detection technique.
• To demonstrate its utility in microscopic imaging and chemical sensing.

Main Methods:

• Development of a flexible software-based photon-counting lock-in implementation.
• Experimental characterization of amplitude and phase noise.
• Evaluation of noise reduction capabilities for illumination, dark counts, and background suppression.

Main Results:

• Achieved amplitude resolution of 4.5% and phase resolution of 13 degrees with 1000 counted photons.
• Demonstrated that noise levels approach the theoretical limit of photonic shot noise.
• Successfully reduced illumination noise, detector dark count noise, and background signals.

Conclusions:

• The photon-counting lock-in offers significant signal-to-noise benefits over conventional methods.
• Its high sensitivity and noise reduction capabilities make it suitable for demanding optical measurements.
• Phase detection is particularly valuable for imaging dynamic processes in microscopic systems using fluorescent probes.