Diffraction phase microscopy with white light
View Patent ↗A microscope and methods for obtaining a phase image of a substantially transparent specimen. Light collected from a specimen illuminated by a temporally incoherent source is diffracted into a first order and either the zeroth or first order is low-pass filtered in a Fourier transform plane before the orders are recombined at a focal plane detector. By low pass filtering the first order diffracted beam into a plurality of wavelengths, a spectrally- and spatially-resolved quantitative phase image of the specimen is obtained.
1. A diffraction phase microscope comprising:
a. a temporally incoherent source of an illuminating beam for illuminating a specimen;
b. an objective lens for collecting light from the source transmitted through the specimen and forming an image at an output port;
c. a grating for relaying a zeroth order beam and for diffracting the image into a first-order diffracted beam;
d. a first Fourier lens for transforming the zeroth-order beam and first-order diffracted beam into respective Fourier transform fields in a Fourier transform plane;
e. a Fourier transform space mask for low-pass filtering one of the zeroth-order beam and the first-order beam in the Fourier transform plane; and
f. a second Fourier lens for recombining the zeroth-order beam and first-order diffracted beam at a focal plane detector.
2. A diffraction phase microscope in accordance with claim 1 , further comprising a condenser aperture disposed between the temporally incoherent source and the specimen for creating a substantially spatially coherent illumination beam in a sample plane.
3. A diffraction phase microscope in accordance with claim 1 , wherein the Fourier transform space mask is implemented by a spatial light modulator.
4. A diffraction phase microscope in accordance with claim 1 , wherein the grating is a transmission grating.
5. A diffraction phase microscope in accordance with any of claims 1 - 4 , wherein the Fourier transform space mask includes a pinhole for transmitting the zeroth-order beam as a reference beam.
6. A diffraction phase microscope in accordance with any of claims 1 - 4 , wherein the Fourier transform space mask includes a plurality of pinholes for transmitting the first-order beam as a reference beam specific to a spectral range.
7. A method for obtaining a phase image of a substantially transparent specimen, the method comprising:
a. illuminating the specimen with substantially temporally incoherent light;
b. forming a transmission image of the specimen in an image plane;
c. dispersing the transmission image with a grating into zeroth and first order beams;
d. low-pass filtering one of the zeroth-order and the first-order beam with a Fourier transform space mask in a Fourier plane of a Fourier lens;
e. interfering the zeroth- and first-order beams at a focal plane detector; and
f. retrieving a spatially resolved quantitative phase image of the specimen.
8. A method in accordance with claim 7 , wherein the first-order beam is filtered by means of a plurality of pinholes for selecting a reference beam at wavelengths characterizing a specified spectral range.
9. A method in accordance with claim 7 , wherein retrieving a spatially resolved quantitative phase image is performed by applying a spatial Hilbert transform.
10. A method in accordance with claim 7 , wherein retrieving a spatially resolved quantitative phase image is performed by applying local derivatives of an interferogram obtained at the focal plane detector.
11. A method in accordance with claim 7 , wherein forming the transmission image includes illuminating the phase object with substantially spatially coherent illumination.
12. A method in accordance with claim 7 , where the illumination is substantially incoherent.