US 12,405,215 B2
Asymmetric quadrature interferometry for thin film interference suppression in optical photothermal infrared spectroscopy
Craig Prater, Santa Barbara, CA (US); Derek Decker, Carmel, CA (US); and David Grigg, Santa Barbara, CA (US)
Assigned to Photothermal Spectroscopy Corp., Santa Barbara, CA (US)
Filed by Photothermal Spectroscopy Corp., Santa Barbara, CA (US)
Filed on Apr. 14, 2023, as Appl. No. 18/300,858.
Prior Publication US 2024/0353324 A1, Oct. 24, 2024
Int. Cl. G01N 21/35 (2014.01); G01N 21/3563 (2014.01)
CPC G01N 21/3563 (2013.01) 22 Claims
OG exemplary drawing
 
1. A method of operating a photothermal infrared microscope, the method comprising:
a) illuminating a region of a sample with a pump beam of infrared radiation;
b) dividing a beam of probe radiation onto at least two paths, the at least two paths including a first path towards a sample and a second path towards a reference reflector;
c) directing probe radiation on the first path to illuminate the sample at least partially overlapping the infrared illuminated region of the sample, wherein the probe radiation interacts with at least two surfaces of the sample to create interfering radiation;
d) collecting the interfering radiation from the sample as collected probe light;
e) recombining the collected probe light with probe radiation reflected from the second path to form recombined light;
f) dividing the recombined light between at least two detectors;
g) using signals from the at least two detectors to generate a signal indicative of infrared absorption by the sample that at least partially suppresses effects of thin film interference from the interfering radiation.