Photothermal microscopy using whispering gallery microcavities

A detector system for use in a photothermal microscopy system, the detector system comprising:

• a microtoroid optical resonator configured to operate in a whispering gallery mode (WGM) and configured to accommodate a particle of interest, the microtoroid optical resonator including a pillar below a top section of the microtoroid optical resonator, the pillar formed from a different material than the top section of the microtoroid optical resonator, wherein:
• at least a portion of the microtoroid optical resonator is positioned to receive a modulated pump laser light with a first wavelength and an amplitude modulation frequency that is less than 1000 Hz, and
• the microtoroid optical resonator is configured to receive a probe laser light with a second wavelength, the second wavelength being different than the first wavelength,
• a photodetector positioned to receive light from the microtoroid optical resonator and produce electrical signals or information corresponding to the light received thereon;
• and
• a proportional-integral-derivative (PID) controller communicatively coupled to the photodetector to receive the electrical signals or the information from the photodetector, wherein an output of the PID controller includes information indicative of shifts in resonance frequency of the microtoroid optical resonator in response to illumination of the microtoroid optical resonator with the amplitude modulated laser light.

A method for detecting a particle in a photothermal microscopy system, the method comprising:

• Illuminating, with a pump laser light at a first wavelength, at least a portion of a top section of an optical resonator that is operating in a whispering gallery mode (WGM), the top section accommodating the particle,
• wherein the pump laser light has an amplitude modulation frequency that is less than 1000 Hz, wherein:
• the photothermal microscopy system includes a photodetector positioned to receive light from the optical resonator and a proportional-integral-derivative (PID) controller communicatively coupled to the photodetector to receive electrical signals or the information from the photodetector, the PID controller further communicatively coupled to a probe laser to at least partially control an operation of the probe laser, the probe laser providing probe laser light with a second wavelength that is coupled into the optical resonator, the second wavelength being different than the first wavelength;
• and
• using an output of the PID controller to detect shifts in resonance frequency of the optical resonator indicative of a presence of the particle.