Apparatus and method to convert a regular bright-field microscope into a PS-QPI system
An apparatus, system, and related methods for the conversion of a regular bright-field microscope into a PS-QPI (Polarization-Sensitivity and Quantitative Phase Imaging) microscope system. A regular bright-field microscope is converted by insertion of a polarizing element in the illumination path and a Fresnel biprism in the image space of the system. The converted system is suitable for real-time quantitative PS phase imaging in a broad number of biological applications aimed at understanding cell growth and dynamic changes occurring during physiological processes, as well as identification of cell/tissue screening and diagnosis.
1 . A method of measuring the polarimetric properties of birefringent samples, comprising the steps of:
providing a polarization-sensitive quantitative phase imaging (PS-QPI) system comprising
a microscope comprising an illumination source, a microscope objective lens and a tube lens, configured to magnify an image of a sample;
a polarizing element configured to orient a polarization state of the illumination source;
a Fresnel biprism; and
a sensor or detector;
sequentially rotating the polarizing element in a controlled way to change the illumination polarization state;
generating and recording holograms for each orientation angle of the polarizing element;
reconstructing an unwrapped phase map for each orientation angle;
selecting maximum and minimum values of the reconstructed phase map to generate an ordinary phase map and an extraordinary phase map for each orientation angle; and
calculating phase difference between the extraordinary phase map and the ordinary phase map to generate a retardance map.
2 . The method of claim 1 , wherein the sensor or detector is a two-dimensional detector configured to record an image to a computer.
3 . The method of claim 1 , wherein the sensor or detector is a CCD or CMOS configured to record an image to a computer.
4 . The method of claim 1 , wherein the illumination source is spatially and temporally coherent.
5 . The method of claim 1 , wherein the illumination source comprises a diode laser, gas laser, discharge tube, light-emitting diode with limited spectral bandwidth, a wide-band light source, or an incandescent and/or fluorescent light source with bandpass filters configured to limit spectral bandwidth.
6 . The method of claim 1 , wherein the polarizing element comprises a linear polarizer or a waveplate.
7 . The method of claim 1 , wherein the polarizing element is mounted in a rotational cage or mount.
8 . The method of claim 1 , wherein the microscope is a commercial bright-field microscope.
9 . The method system of claim 1 , wherein the Fresnel biprism is configured to generate two copies of the magnified image of the sample with some angle to each other.
10 . The method of claim 9 , wherein the Fresnel biprism comprises two prisms joined at respective bases.
11 . The method of claim 9 , wherein the system forms a digital hologram by coherent superposition or interference of the two copies of the magnified image.
12 . The method of claim 1 , further comprising an afocal imaging component comprising a first converging lens and a second converging lens with a common Fourier plane therebetween, and a pinhole located at the common Fourier plane.
13 . The method of claim 12 , wherein the afocal imaging component magnifies the image of the sample.
14 . The method of claim 12 , where the pinhole comprises a spatial filter configured to filter medium and high frequency content of one of a pair of images generated by the Fresnel biprism.
15 . The method of claim 1 , further comprising:
a secondary polarization module comprising a second illumination source and a second polarizing element, wherein the secondary polarization module introduces a reflected image of the sample into an optical path; and
a beam splitter placed between the tube lens and the Fresnel biprism.