Photothermal imaging device and system

1. A method for detecting infrared light absorption in a sample with submicron resolution, the method comprising the steps:

a) illuminating a region of the sample with a pump beam generated by a first light source, wherein at least a portion of the pump beam is absorbed by the region of the sample;

b) illuminating the region of the sample with a probe beam generated by a second light source, wherein the probe beam has a first wavelength;

c) collecting, by a detector, a portion of the probe beam coming from the region of the sample; and

d) analyzing the collected light to construct a signal indicative of infrared absorption by the region of the sample with submicron spatial resolution,

wherein illuminating the region of the sample with the pump beam comprises illuminating a first side of the region of the sample with the pump beam,

wherein illuminating the region of the sample with the probe beam comprises illuminating a second side of the region of the sample with the probe beam, and

wherein the first side of the region of the sample is opposite to the second side of the region of the sample.

2. The method according to claim 1 , wherein analyzing the collected light comprises the steps:

generating, based on the collected probe light and the first wavelength, a signal indicative of the portion of the pump beam absorbed by the region of the sample, wherein the signal represents an amount of infrared light absorbed by the region of the sample.

3. The method according to claim 1 , further comprising the step of repeating steps (a)-(d) at plurality of regions on the sample to construct a map of the signal indicative of infrared absorption with a spatial resolution of less than 1 micron.

4. The method according to claim 1 ,

wherein the pump beam travels along a first pathway toward the region of the sample,

wherein the probe beam travels along a second pathway toward the region of the sample, and

wherein the first pathway does not intersect with the second pathway.

5. The method according to claim 1 ,

wherein the pump beam is directed toward a first sample surface,

wherein the probe beam is directed toward a second sample surface, and

wherein the first sample surface is adjacent to the second sample surface.

6. The method according to claim 1 ,

wherein the pump beam is directed toward a first sample surface,

wherein the probe beam is directed toward a second sample surface, and

wherein the first sample surface is the same as the second sample surface.

7. The method according to claim 1 , further comprising the step:

modulating the pump beam according to a first modulation frequency.

8. The method according to claim 7 , wherein the first modulation frequency is greater than or equal to 100 kHz.

9. The method according to claim 1 , wherein the first light source is a mid-infrared laser having at least one emission wavelength within the range of 3 to 25 micrometers.

10. The method according to claim 1 , wherein the second light source is a visible light laser having at least one emission wavelength that is less than or equal to 800 nanometers.

11. The method according to claim 1 , further comprising the step:

focusing, by a reflective objective, the pump beam onto the region of the sample.

12. The method according to claim 1 , further comprising the step:

focusing, by a refractive objective, the probe beam onto the region of the sample.

13. The method according to claim 1 , wherein the analyzing step comprises:

sending a signal from the detector to a lock-in amplifier configured to determine at least one of (i) an amplitude and (ii) a phase of the probe beam reflecting from the region of the sample;

providing the lock-in amplifier a reference signal to a modulation frequency of the pump laser; and

using the lock-in amplifier to construct the signal indicative of infrared absorption by the region of the sample.

14. The method according to claim 1 , wherein the sample is held by a cell adapted for high infrared transmission, wherein the cell includes sapphire windows.

15. The method according to claim 1 , wherein absorption of infrared radiation from the pump beam by the sample results in a temperature increase of the region of the sample and wherein propagation of the probe beam is affected by a thermal lens formed by the temperature increase.

16. A system for detecting infrared light absorption in a sample with submicron resolution, the system comprising:

a first light source operable to illuminate a region of the sample with a pump beam of mid infrared radiation, wherein at least a portion of the pump beam is absorbed by the region of the sample;

a second light source operable to illuminate the region of the sample with a probe beam;

a detector operable to collect and measure at least a portion of the probe beam coming from the region of the sample; and

a signal processing device configured to generate, based on the probe light collected by the detector, a signal indicative of an amount of infrared light absorbed by the region of the sample, with sub-micron spatial resolution,

wherein the first light source is arranged to illuminate a first side of the region of the sample with the pump beam,

wherein the second light source is arranged to illuminate a second side of the region of the sample with the probe beam, and

wherein the first side of the region of the sample is opposite to the second side of the region of the sample.

17. The system according to claim 16 , wherein the system further comprises:

a movable platform coupled to the sample and operable to move the sample in two dimensions with respect to the first light source and the second light source to illuminate a plurality of regions of the sample with the pump beam and probe beam;

and wherein the signal processing unit generates the signal indicative of infrared absorption of light by the sample at the plurality of regions of the sample to generate an image indicated of infrared absorption of the sample.

18. The system according to claim 16 ,

wherein the first light source is arranged to emit the pump beam that travels along a first pathway toward the region of the sample,

wherein the second light source is arranged to emit the pump beam that travels along a second pathway toward the region of the sample, and

wherein the first pathway does not intersect with the second pathway.

19. The system according to claim 16 ,

wherein the first light source is arranged to emit the pump beam toward a first sample surface,

wherein the second light source is arranged to emit the pump beam toward a second sample surface, and

wherein the first sample surface is adjacent to the second sample surface.

20. The system according to claim 16 ,

wherein the first light source is arranged to emit the pump beam toward a first sample surface,

wherein the second light source is arranged to emit the pump beam toward a second sample surface, and

wherein the first sample surface is the same as the second sample surface.

21. The system according to claim 16 , wherein the first light source is further operable to:

modulate the pump beam according to a first modulation frequency.

22. The system according to claim 21 , wherein the first modulation frequency is greater than or equal to 100 kHz.

23. The system according to claim 16 , wherein the first light source is a mid-infrared laser having at least one emission wavelength within the range of 3 to 25 micrometers.

24. The system according to claim 16 , wherein the second light source is a visible light laser having at least one emission wavelength that is less than or equal to 800 nanometers.

25. The system according to claim 16 , further comprising:

a reflective objective adapted to focus the pump beam onto the region of the sample.

26. The system according to claim 16 , further comprising:

a refractive objective adapted to focus the probe beam onto the region of the sample.

27. The system according to claim 16 , wherein the signal processing device is a lock-in amplifier configured to:

sending a signal from the detector;

receive a signal indicative of a modulation frequency of the pump beam;

determine at least one of (i) an amplitude and (ii) a phase of the probe beam coming from the region of the sample; and

generate the signal indicative of the amount of infrared light absorbed by the region of the sample based on the determined at least one of (i) the amplitude and (ii) the phase of the probe beam reflecting from the region of the sample.

28. The system according to claim 16 , further comprising:

a cell adapted for high infrared transmission and configured to hold the sample, wherein the cell includes sapphire windows.

29. A method for detecting infrared light absorption in a sample with submicron resolution, the method comprising the steps:

a) illuminating a region of the sample with a pump beam generated by a tunable source of mid-infrared radiation, wherein at least a portion of the pump beam is absorbed by the region of the sample at least one wavelength generated by the tunable source;

b) illuminating the region of the sample with a probe beam generated by a second light source, wherein the probe beam has a wavelength shorter than the pump beam and a Gaussian beam width of less than 2.33 micrometers;

c) collecting by a detector at least of a portion of the probe beam coming from the region of the sample;

d) generating, based on probe light collected by the detector, a signal indicative of an amount of infrared light absorbed by the region of the sample with sub-micron spatial resolution;

e) repeating steps (a)-(d) at a plurality of wavelengths of the tunable source of mid-IR radiation.

30. The method according to claim 29 , further comprising:

generating from steps (a)-(e) a signal indicative of an absorption spectrum of the region of the sample; and

based on the determined absorption spectrum, determining one or more chemical compounds present in the sample.

31. The method according to claim 29 , wherein the probe beam has a Gaussian beam width of less than 0.7 micrometers.

32. A system for detecting infrared light absorption in a sample with submicron resolution, the system comprising:

a first light source operable to illuminate a region of the sample with pump beam generated by a tunable mid-infrared light source operable to generate radiation at a plurality of wavelengths; and wherein the sample absorbs at least a portion of the pump beam at at least one wavelength of the tunable light source;

a second light source operable to illuminate the region of the sample with a probe beam generated by a second light source, wherein the probe beam has a shorter wavelength than the mid-IR pump beam and a Gaussian beam width of less than 2.33 micrometers;

a detector operable to collect at least a portion of the probe beam having coming from the region of the sample;

a signal processing device configured to generate a signal indicative of an amount of mid-infrared light absorbed by the region of the sample with sub-micron spatial resolution at a plurality of wavelengths of the tunable IR pump beam.

33. The system according to claim 32 , wherein the system is further configured to:

generate a signal indicative of an absorption spectrum of the sample based on the signal indicative of the mid-IR absorption of the region of the sample at the plurality of wavelengths of the tunable IR pump beam; and

based on the determined absorption profile, determine one or more chemical compounds present in the sample.

34. The system according to claim 32 , wherein the probe beam has a Gaussian beam width of less than 0.7 micrometers.