Upconverting and time-gated two-dimensional infrared transillumination imaging

• US 5,451,785 A
• Filed: 03/18/1994
• Issued: 09/19/1995
• Est. Priority Date: 03/18/1994
• Status: Expired due to Fees

• Current Assignee: SRI International, Inc.
• Original Assignee: SRI International, Inc.
• Inventors: Faris, Gregory W.
• Primary Examiner(s): Fields, Carolyn E.
• Assistant Examiner(s): Glick, Edward J.
• Application Number:
  US08/215,123
• Time in Patent Office: 550 Days
• Field of Search: 250/330, 250/332, 250/358.1, 128/664
• US Class Current: 250/330
• CPC Class Codes: A61B 5/0086 using infrared radiation
• CPC Class Codes: G01N 21/4795 spatially resolved investigating of object in scattering medium in vivo A61B
• CPC Class Codes: G02F 1/3534 Three-wave interaction, e.g. sum-difference frequency generation G02F1/3532 takes precedence
• CPC Class Codes: G02F 1/39 for parametric generation or amplification of light, infrared or ultraviolet waves

Abstract

A method and apparatus for direct two-dimensional transillumination imaging of a sample immersed in or including a scattering medium at infrared to near-infrared wavelengths. Frequency conversion and time-gating techniques in the infrared and near-infrared range are used to enhance two-dimensional image collection and detection. The apparatus includes a probe radiation source for applying a probe beam in the infrared to near-infrared frequency range to the sample. The probe beam is spread to cover a two-dimensionally extending area of the sample to be imaged. After interacting with the sample, the probe beam is representative of a two-dimensional image of the covered sample area. In one embodiment the apparatus includes a time-gating arrangement for selecting a temporal portion of the probe beam in a narrow time window representative of early arriving photons transmitted through the scattering medium and providing a time-gated beam representative of the two-dimensional image of the sample area. A reference beam interacts with a nonlinear medium to shift the frequency of the probe beam to a different frequency, which may lie outside the infrared to near-infrared range. In many applications of the apparatus the frequency will be shifted upward to a frequency higher than near-infrared. The nonlinear interaction occurs in such a manner so as not to destroy the two-dimensional image carrier by the time-gated beam. A detector operative at the shifted frequency detects the time-gated and frequency-shifted beam to directly record the two-dimensional image.

Claims

1. Transillumination imaging apparatus for obtaining a two-dimensional image of a sample through a scattering medium, comprising:

a probe radiation source for applying a probe beam of radiation to the sample, said probe beam having a frequency in the infrared to near-infrared range;

optical means for spreading said probe beam to cover an area of said sample extending in two dimension, wherein said probe beam is representative of a two-dimensional image of said area after interaction with said sample;

time-gate means for selecting a temporal portion of said probe beam in a narrow time window representative of early arriving photons transmitted through said scattering medium and providing a time-gated beam representative of a two-dimensional image of said sample area;

wherein said time-gate means comprises;

a reference radiation source providing a reference beam of radiation at a reference frequency directed along an optical path that avoids said sample and said scattering medium, said reference frequency being higher than said infrared to near-infrared range; and

coupling means for collinearly mixing said reference beam and said probe beam after interaction with said sample to provide said time-gated beam;

means for adjusting the length of said reference beam optical path so as to adjust the length of the narrow time window of the selected temporal portion of said probe beam;

upconversion means for shifting said time-gated beam to an upcoversion frequency higher than said probe beam frequency without destroying said two-dimensional image; and

a detector operative at said upconversion frequency for detecting said upconverted time-gated beam representative of said two-dimensional image at said upconversion frequency.

2. The apparatus of claim 1, further comprising a crystal receiving said reference beam and said probe beam after interaction with said sample, said crystal interacting nonlinearly with said reference and probe beams to provide said upconverted time-gated beam.

3. The apparatus of claim 2 wherein said probe radiation source and said reference radiation source are provided by a single laser.

4. The apparatus of claim 3 wherein said laser comprises a Q-switched mode-locked laser.

5. The apparatus of claim 3 wherein said means for adjusting the length of said reference beam optical path comprises a prism mounted for movement in a linear direction and disposed in said optical path such that said optical path enters and exits said prism parallel to said linear direction, whereby said path length may be adjusted by moving said prism in said linear direction.