Method and apparatus for performing second harmonic optical coherence tomography

A method of performing optical tomography of a sample comprising:

• providing a source of at least partially coherent broadband radiation through an interferometer having a sample arm for probing the sample and a reference arm;
• scanning the sample with the source of radiation through the interferometer;
• generating first and second harmonics from the sample and from a nonlinear thin crystal in the reference arm;
• detecting interference fringes of the first and second harmonics radiation backscattered from the sample into the interferometer;
• processing the detected interference fringes to determine first and second harmonics OCT signals of the detected backscattered interference fringes at each pixel in a data window;
• and
• generating a tomographic image of the sample based on the first and second harmonics OCT interference fringes at different spatial locations in the sample disDlayed as different pixels in a final image.

An apparatus for performing optical tomography of a sample in which second harmonics of a radiation signal can be generated comprising:

• a source of at least partially coherent broadband radiation;
• an interferometer coupled to the source having and a reference arm and a sample arm for probing the sample;
• a scanner for scanning the sample with radiation from the source provided through the interferometer;
• a nonlinear thin crystal in the reference arm for generating second harmonics;
• a detector for detecting interference fringes of the first and second harmonics of the radiation backscattered from the sample into the interferometer;
• and
• a processor coupled to the detector to determine first and second harmonic OCT signals of the detected backscattered interference fringes different optical delays between the sample and reference arms, and to simultaneously generate a tomographic image of the sample based on the first and second harmonics OCT interference fringes at different spatial locations in the sample displayed as different pixels in a final image.

An improvement in an OCT tomographic imaging system having an interferometer with a reference arm and sample arm comprising:

• means for generating a second harmonic frequency in the reference arm;
• means for combining the second harmonic frequency from the reference arm and a second harmonic frequency from the sample in the sample arm to produce a second harmonic interference fringe signal;
• and
• means for detecting the second harmonic interference fringe signal to enable the OCT tomographic imaging system to produce an image derived from the second harmonic interference fringes at different spatial locations in the sample displayed as different pixels in a final image.

A method for second harmonic optical coherence tomography of a sample comprising:

• generating light at a fundamental frequency;
• coupling the light at a fundamental frequency into an interferometer having an optical path in a reference arm and in a sample arm;
• generating a second harmonic of the light in the optical path of the reference arm;
• generating a second harmonic of the light in the optical path of the sample arm depending on the nonlinear optical properties and optical scattering characteristics of the sample;
• combining the second harmonic of the light from the reference arm and the sample arm to generate a second harmonic interference fringes at different spatial locations in the sample displayed as different pixels in a final image;
• and
• detecting the second harmonic interference fringe signal based on scattering from the sample.

An improvement in a method of OCT tomographic imaging using an interferometer with a reference arm and sample arm comprising:

• generating a second harmonic frequency in the reference arm;
• combining the second harmonic frequency from the reference arm and a second harmonic frequency from the sample in the sample arm to produce a second harmonic interference fringe signal;
• and
• detecting the second harmonic interference fringe signal to enable the OCT tomographic imaging system to produce an image derived from the second harmonic interference fringes at different spatial locations in the sample displayed as different pixels in a final image.

A method for performing optical tomography of a sample in which second harmonics of a radiation signal comprising:

• generating at least partially coherent broadband radiation;
• coupling the radiation to an interferometer having and a reference arm and a sample arm for probing the sample;
• scanning the sample with radiation provided through the interferometer;
• generating second harmonics in the reference arm;
• detecting interference fringes of the first and second harmonics of the radiation backscattered from the sample into the interferometer;
• detecting first and second harmonic OCT signals of the detected backscattered interference fringes at each pixel in a data window;
• and
• simultaneously generating a tomographic image of the sample based on the first and second harmonics OCT interference fringes at different spatial locations in the sample displayed as different pixels in a final image.

An apparatus for performing optical tomography of a sample in which second harmonics of a radiation signal can be generated comprising:

• a source of at least partially coherent broadband radiation;
• a fiber-based interferometer coupled to the source having a reference arm and a sample arm for probing the sample;
• a scanner for scanning the sample with radiation from the source provided through the interferometer;
• a nonlinear thin crystal in the reference arm for generating second harmonics;
• a detector for detecting interference fringes of the first and second harmonics of the radiation backscattered from the sample into the interferometer;
• and
• a processor coupled to the detector to determine first and second harmonic OCT signals of the detected backscattered interference fringes at each pixel in a data window, and to simultaneously generate a tomographic image of the sample at each pixel based on the first and second harmonics OCT interference fringes.

An improvement in an OCT tomographic imaging system using an interferometer with a reference arm and sample arm to image a sample comprising:

• a nonlinear crystal for generating third harmonic frequency in the reference arm;
• means for combining the third harmonic frequency from the nonlinear crystal in the reference arm and any third harmonic frequency returned from the sample in the sample arm to produce a third harmonic interference fringe signal;
• and
• means for detecting the third harmonic interference fringe signal to enable the OCT tomographic imaging system to produce an image derived from the third harmonic interference fringe signal.

An improvement in an OCT tomographic imaging system using an interferometer with a reference arm and sample arm to image a sample comprising:

• a coherent Raman reference for generating a coherent Raman frequency in the reference arm;
• means for combining the coherent Raman frequency from the coherent Raman reference in the reference arm and any Raman frequency from the sample in the sample arm to produce a coherent Raman interference fringe signal;
• and
• means for detecting the coherent Raman interference fringe signal to enable the OCT tomographic imaging system to produce an image derived from the coherent Raman interference fringe signal.