Optically super-resolved infrared impulse spectroscopy (osiris)

Description (excerpt)

CROSS-REFERENCE TO RELATED APPLICATIONS The present application is a Continuation Application of the U.S. Non-provisional patent application Ser. No. 18/096,250 filed Jan. 12, 2023, entitled “OPTICALLY SUPER-RESOLVED INFRARED IMPULSE SPECTROSCOPY (OSIRIS)-A TECHNIQUE FOR HIGH CONTRAST CHEMICAL IMAGING OF CHEMICAL COMPOSITION”, which claimed the benefit of priority to the U.S. Provisional Application No. 63/298,724, filed on Jan. 12, 2022, entitled “OPTICALLY SUPER-RESOLVED INFRARED IMPULSE MICRO-SPECTROSCOPY: A TECHNIQUE FOR RAPID, HIGH CONTRAST LABEL-FREE CHEMICAL IMAGING.” This application and all other publications and patent documents referred to throughout this Continuation Application are incorporated herein by reference in their entirety. FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT The United States Government has ownership rights in this invention. Licensing inquiries may be directed to Office of Technology Transfer, US Naval Research Laboratory, Code 1004, Washington, D.C. 20375, USA; +1.202.767.7230; nrltechtran@us.navy.mil, referencing Navy Case No. 210948-US3. BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to spectroscopic imaging. Description of the Prior Art There has been significant recent interest in a novel microscopy technique wherein the change in the signal of a short wavelength scanning confocal probe is measured as the sample is heated by a modulated infrared laser. This signal, denoted (Ω, is related to both the probe intensity and the infrared induced change in temperature (See FIG. 1 .). In this way, the chemical composition of the sample—through the infrared absorption spectrum k(λ)—is revealed at optical resolutions. A high duty cycle infrared (IR) pump, typically a Quantum Cascade Laser,—5%-50% duty cycle1, 100-500 kHz repetition rate-has been used. The signal Ω is extracted in the frequency domain via demodulation of the continuous wave (CW) probe signal. Virtual lock-in demodulation, has been used to increase the image acquisition rate, at some cost of spatial resolution. Virtual lock-in detection works by strobing (flashing) the probe to capture images on a camera array with higher temporal resolution than the camera would typically be capable of. The signal Ω can be inferred by comparing images where the infrared pump is both on and off. The increase in speed is provided by the highly parallel acquisition provided by the camera array. However, this increase in speed comes at the cost of the confocality, which is desirable for increased resolution, particularly in 3D imaging (tomography). Collectively, these approaches, which has come to be known as Mid Infrared Photothermal (MIP) imaging, has demonstrated the potential to access a regime that has long been considered something of a holy grail for microscopy—real-time label-free chemical microscopy in biological samples. However, significant challenges persist. The sensitivity is limited, particularly when imaging resolution scale objects. The dependence of the signal on the inclusion size and fractal dimension complicates the data analysis greatly; thus far, there is no method to extract the chemical composition (concentration) from the measured data. It seems likely that such analysis will remain intractable with the existing experimental techniques/hardware. This is of particular concern since the raw data Ω(x, y, z, t, λ), is difficult to visualize. Moreover, it lacks the intuitive character that typically makes imaging techniques so powerful. This unintuitive aspect is amplified when the sample is not substantially known a priori. BRIEF SUMMARY OF THE INVENTION The high-duty cycle approach used in MIP is inconsistent with the thermal transport within the sample. This not only results in the MIP technique having low sensitivity, but it also results in small inclusions within the sample heating less than large inclusions. The result is that the signal depends not only on the chemical composition of the sample at a given pixel, but also the surrounding composition. Because of this complication, there is no clear method to extract the chemical composition from the MIP image. The present invention provides for a low duty cycle (pulsed) technique, called Optically Super-resolved InfraRed Impulse Spectroscopy (OSIRIS), to overcome the sensitivity and analysis challenges inherent in MIP. OSIRIS differs from MIP in the following ways: An infrared pulse, which is short compared to the thermal time constant of resolution scale objects within the sample. This results in heating that is proportional to the analyte's absorptivity and concentration, and NOT of the size of the analyte inclusion or its surroundings. This makes it possible to extract the concentration di