Enhanced surface-selective spectroscopy using broad-band heterodyne-detected sum frequency generation
Method and apparatus for performing spectroscopy, include the combining of first and second light beams to form a reference beam, focusing the first and second light beams and the reference beam onto a sample, receiving a reflected light beam from the sample at a monochromator, and viewing a predetermined wavelength band of the reflected light beam from the monochromator. Portions of the first and second light beams, which may be visible and IR forms of electromagnetic energy, are heterodyned through a crystal. A monochromator receives a reflection of the reference beam from the sample, and Fourier transformation is performed on the output of the monochromator. The first and second beams of electromagnetic energy can be split to form first and second component beams and the reference beam, all of which are propagated to the sample.
1. A method of performing spectroscopy, the method comprising the steps of:
combining in an optical circuit first portions of first and second input light beams to form a reference beam;
focusing second portions of the first and second light beams and the reference beam onto a sample desired to be investigated;
receiving a reflected light beam from the sample at an input of a monochromator; and
viewing a predetermined wavelength band of the reflected light beam at an output of the monochromator.
2. The method of claim 1 wherein said step of combining comprises the step of propagating the first portions of the first light beam and the second light beam through a crystal.
3. The method of claim 2 , wherein said step of propagating the first portions of the first light beam and the second light beam through a crystal comprises the further step of difference frequency mixing.
4. The method of claim 2 , wherein the first light beam is an IR light, the second light beam is a visible light, and the crystal is formed of KNbO 3 .
5. The method of claim 1 , wherein said step of viewing comprises the further step of propagating the predetermined wavelength band of the reflected light beam from the output of the monochromator to a camera.
6. The method of claim 1 , wherein there is further provided the step of subjecting the predetermined wavelength band of the reflected light beam to inverse Fourier transformation to produce a corresponding time-domain representation of the predetermined wavelength band of the reflected light beam.
7. The method of claim 6 , the time-domain representation of the predetermined wavelength band of the reflected light beam is subjected to the step of fast Fourier transform (FFT) and the real part of the resulting frequency domain representation is extracted.
8. The method of claim 7 , wherein there is further provided the step of determining an absolute value of the real part of the resulting frequency domain representation.
9. The method of claim 1 , wherein there is further provided the step of interposing an optical delay stage in the path of a selected one of the first and second light beams.
10. A spectroscopy system comprising:
an optical circuit having first and second inputs for receiving respective ones of first and second beams of electromagnetic energy;
a beam splitter for splitting the first beam of electromagnetic energy into first and second sub-beams of electromagnetic energy;
a crystal for propagating the first sub-beam of electromagnetic energy of the first beam of electromagnetic energy and the second beam of electromagnetic energy simultaneously, to produce a combined reference beam of electromagnetic energy; and
a reflector element for directing the reference beam toward a sample that is desired to be investigated.
11. The spectroscopy system of claim 10 , wherein there is further provided a monochromator for receiving a reflection of the reference beam from the sample.
12. The spectroscopy system of claim 11 , wherein there is further provided an analysis system for conducting a Fourier transformation on the output of said monochromator.
13. The spectroscopy system of claim 10 , wherein said reflector element additionally direct the second beam of electromagnetic energy and the second sub-beam of electromagnetic energy of the first beam of electromagnetic energy toward the sample that is desired to be investigated.
14. The spectroscopy system of claim 10 , wherein said crystal is a AgGaS 2 crystal.
15. The spectroscopy system of claim 10 , wherein said crystal is a KNbO 3 crystal.
16. The spectroscopy system of claim 10 , wherein there is further provided an optical delay stage in the propagation path of the first beam.
17. A method of performing spectroscopy, the method comprising the steps of:
splitting each of first and second beams of electromagnetic energy to form respectively associated first and second component beams for each of the first and second beams of electromagnetic energy;
combining the first component beams of each of the first and second light beams in a crystal to form a reference beam; and
focusing the reference beam onto a sample desired to be investigated.
18. The method of claim 17 , wherein said step of focusing the reference beam onto a sample desired to be investigated comprises the further step of focusing the second component beams of each of the first and second light beams onto the sample desired to be investigated.
19. The method of claim 18 , wherein there is further provided the step of receiving electromagnetic energy reflected from the sample at an input of a monochromator.
20. The method of claim 19 , wherein prior to performing said step of receiving electromagnetic energy reflected from the sample at an input of a monochromator there is provided the further step of collimating the electromagnetic energy reflected from the sample.