Matched pulse stimulated raman scattering

• US 8,300,228 B2
• Filed: 10/20/2009
• Issued: 10/30/2012
• Est. Priority Date: 10/21/2008
• Status: Active Grant

• Current Assignee: Board of Trustees of The University of Illinois
• Original Assignee: Board of Trustees of The University of Illinois
• Inventors: Marks, Daniel L., Geddes, Joseph B. III, Boppart, Stephen A.
• Primary Examiner(s): Chowdhury, Tarifur
• Assistant Examiner(s): Cook, Jonathon
• Application Number:
  US12/582,168
• Publication Number:
  US 20100208252A1
• Time in Patent Office: 1,106 Days
• Field of Search: 356/450, 356/451
• US Class Current: 356/451
• CPC Class Codes: G01J 3/10 Arrangements of light sources specially adapted for spectrometry or colorimetry
• CPC Class Codes: G01J 3/44 Raman spectrometry; Scattering spectrometry ; Fluorescence spectrometry
• CPC Class Codes: G01J 3/4531 Devices without moving parts
• CPC Class Codes: G01J 9/02 by interferometric methods using interferometers for measuring optically the linear dimensions of objects G01B9/02

Abstract

Methods and apparatus for selectively driving the vibrations of normal modes of a target molecule into coherence using stimulated Raman scattering. In concert, many vibrations produce a larger anti-Stokes signal than a single vibration. The same illumination does not drive other molecules to have coherent vibrations, so these molecules produce a weaker signal. Target and confounder molecules can be distinguished by pulses that drive many vibrations coherently, with applications in coherent Raman microspectroscopy.

Claims

1. A method for identifying the presence of a target molecular species in a sample, the molecular species characterized by a plurality of vibrational modes and a Raman impulse response, the method comprising:

a. defining at least one feature of an exciting electromagnetic pulse on a basis of features of the Raman impulse response of the target species;

b. exciting the sample with the electromagnetic pulse;

c. generating coherent stimulated scattered radiation;

d. interfering the coherent stimulated radiation with a reference pulse so as to cross-correlate the coherent stimulated radiation and the reference pulse, the reference pulse characterized by a relative timing with respect to the exciting electromagnetic radiation;

e. shaping the reference pulse for selectively enhancing a correlation with scatter of the target species;

f. sweeping the delay time so as to measure correlation as a function of delay time; and

g. determining the presence of the target species based at least on a specified criterion applied to correlation as a function of delay time.

2. A method in accordance with claim 1, wherein the reference pulse is derived from the exciting electromagnetic pulse.

3. A method in accordance with claim 1, wherein the step of defining at least one feature of the exciting electromagnetic pulse includes defining a temporal aspect of the pulse.

4. A method in accordance with claim 1, wherein the step of defining at least one feature of the exciting electromagnetic pulse includes shaping an envelope of the pulse.

5. A method in accordance with claim 1, wherein the step of defining at least one feature of the exciting electromagnetic pulse includes defining an envelope amplitude aspect of the pulse.

6. A method in accordance with claim 1, wherein the step of defining at least one feature of the exciting electromagnetic pulse includes defining an envelope phase aspect of the pulse.

7. A method in accordance with claim 1, wherein the step of defining at least one feature of the exciting electromagnetic pulse includes defining a spectral aspect of the pulse.

8. A method in accordance with claim 1, wherein the step of defining at least one feature of the exciting electromagnetic pulse includes shaping the pulse in time to approximate a time-reversal of the Raman impulse response of the target species.

9. A method in accordance with claim 1, wherein the coherent stimulated scattering is anti-Stokes Raman scattering.

10. A method in accordance with claim 1, wherein the coherent stimulated scattering is Stokes Raman scattering.

11. A method in accordance with claim 1, wherein the exciting electromagnetic pulse is shaped to approximate a time-reversal of the Raman impulse response of the target species.

12. A method in accordance with claim 1, wherein the target species is used for generating the reference signal.

13. A method in accordance with claim 1, wherein the step of interfering the anti-Stokes scattered radiation with the reference beam further comprises filtering excitation wavelengths from at least one of the scattered radiation and the reference beam.

14. A method in accordance with claim 1, wherein the step of shaping includes a successive iteration process to achieve an intensity profile positive-definite in time.

15. A method in accordance with claim 1, wherein the step of shaping includes using a reference target sample to define the shape of the exciting electromagnetic pulse without an iterative algorithm.

16. A method in accordance with claim 1, wherein the step of shaping includes using a reference target sample in an environment corresponding to that of the sample to define the shape of the exciting electromagnetic pulse without an iterative algorithm.

17. A method in accordance with claim 1, further including introducing scatterers into the sample to enhance field intensities with respect to the target species.

18. An apparatus for identifying the presence of a target molecular species in a sample, the apparatus comprising:

a. a source of ultrashort electromagnetic pulses;

b. a pulse shaper for shaping pulses generated by the source in a manner exhibiting target species specificity;

c. an interferometer for interfering pulses traversing a sample with reference pulses traversing a reference path;

d. at least one detector for detecting a combination of pulses traversing the sample with reference pulses traversing the reference path;

e. a correlator for determining the presence of the target species based at least on a specified criterion applied to correlation as a function of delay time; and

f. a target sample disposed within the reference path.

19. An apparatus in accordance with claim 18, wherein the reference pulses are derived from the exciting electromagnetic pulse.

20. An apparatus in accordance with claim 18, further comprising a filter for filtering excitation wavelengths from at least one of radiation scattered by the sample and the reference pulses.