Non-interferometric photoacoustic remote sensing (NI-PARS)

An endoscopic device that uses a photoacoustic remote sensing system (NI-PARS) for imaging a subsurface structure in a sample, the endoscopic device comprises:

• a fiber optic cable having an input end and a detection end;
• one or more lasers configured to generate:
• an excitation beam coupled to the input end of the fibre optic cable, wherein in use the excitation beam generates ultrasonic signals in the sample at an excitation location that is adjacent to the detection end of the fiber optic cable, the fiber optic cable focusing the excitation beam below a surface of the sample;
• and
• an interrogation beam coupled to the input end of the fibre optic cable and incident on the excitation location, the fiber optic cable focusing the excitation beam below the surface of the sample, and wherein a portion of the interrogation beam that is indicative of the generated ultrasonic signals is received by the detection end of the fiber optic cable and travels to the input end;
• a non-interferometric detector that receives the returning portion of the interrogation beam at the input end of the fiber optic cable;
• and
• a processor configured to calculate an image of the sample based on a detected intensity modulation of the returning portion of the interrogation beam from below the surface of the sample, wherein the intensity modulation is caused by the excitation beam focused below the surface of the sample.

A non-interferometric photoacoustic remote sensing system (NI-PARS) for imaging a subsurface structure in a sample, comprising:

• one or more lasers configured to generate:
• a pulsed or intensity-modulated excitation beam configured to generate ultrasonic signals in the sample at an excitation location below a surface of the sample;
• and
• an interrogation beam incident on the sample at the excitation location, a portion of the interrogation beam returning from the sample that is indicative of the generated ultrasonic signals;
• wherein the one or more lasers include a single-wavelength source or a multi-wavelength source,
• an optical system that focuses the excitation beam and the interrogation beam below the surface of the sample;
• a non-interferometric detector that detects the returning portion of the interrogation beam;
• a polarizing beam splitter, wherein the interrogation beam is configured to pass through the polarizing beam splitter before reaching the sample;
• a quarter wave plate configured to guide the returning portion of the interrogation beam to the non-interferometric detector;
• and
• a processor configured to calculate an image of the sample based on a detected time-varying intensity modulation of the returning portion of the interrogation beam from below the surface of the sample, wherein the time-varying intensity modulation is caused by the excitation beam focused below the surface of the sample,
• wherein:
• the sample includes tissue;
• the excitation beam and the interrogation beam are focused within 1 mm of the surface of the sample;
• at least one of the excitation beam and the interrogation beam is focused at a depth greater than 1 μm below the surface of the sample;
• the excitation beam and the interrogation beam are confocal;
• and
• the system does not include an ultrasound transducer.