Common-mode digital holographic microscope
A lens-less digital holographic microscope, a reflective digital holographic microscope, and a digital holographic microscope including a plurality of lenses. In one example, the digital holographic microscope includes a single mode fiber collimated light source which provides illumination for both the ‘science’ and ‘reference’ arms, a pair of microscope objectives located side-by side, and illuminated by the common beam, a relay lens whose center is between the two objectives, and a focal plane element where the interference pattern is measured.
1. A digital holographic microscope, comprising:
at least one coherent electromagnetic radiation source emitting electromagnetic radiation;
a collimator positioned to collimate the electromagnetic radiation, to form collimated electromagnetic radiation;
a sample mount positioned such that:
a sample mounted on the sample mount interacts with the collimated electromagnetic radiation to form sample electromagnetic radiation, and
one or more references mounted on the sample mount interact with the collimated electromagnetic radiation to form reference electromagnetic radiation; and
a microscope lens assembly, comprising a first lens separate from a second lens, and a relay lens, positioned such that:
at least a portion of the sample electromagnetic radiation is transmitted through the first lens, and then the relay lens, forming a real image of the sample on a detector,
at least a portion of the reference electromagnetic radiation is transmitted through the second lens, and then the relay lens, forming a reference beam spread over pixels on the detector,
the portion of the sample electromagnetic radiation and the reference beam are directed by the relay lens onto the detector at an angle with respect to each other so as to form an interference pattern on the detector, and
one or more computers can compute an image of the sample using the real image including the interference pattern detected by the detector.
2. The digital holographic microscope of claim 1 , wherein the system is an off-axis digital holographic microscope.
3. The digital holographic microscope of claim 1 , wherein the electromagnetic radiation comprises a single wavelength.
4. The digital holographic microscope of claim 1 , wherein:
the one or more references comprise a plurality of references,
the electromagnetic radiation comprises multiple (fixed or scanned) wavelengths, and the sample mount comprises:
a sample window transmitting the multiple wavelengths to the sample, and
a plurality of reference windows, each of the reference windows transmitting a different one of the wavelengths to one of the plurality of the references.
5. The digital holographic microscope of claim 1 , wherein:
the imaging system has a transmission geometry such that the first lens and the second lens collect at least some of the sample electromagnetic radiation transmitted through the sample.
6. The digital holographic microscope of claim 1 , wherein:
the sample comprises one or more biological cells in a liquid, and
the one or more references each comprise the liquid.
7. The digital holographic microscope of claim 1 , wherein the image has a resolution of less than 1 micrometer over a 0.4 mm×0.4 mm×0.4 mm volume of the sample.
8. The digital holographic microscope of claim 1 , wherein:
positions of the collimator, the sample mount, the sample, the one or more references, the first lens, the second lens, and the relay lens are such that a resolution of the image does not change when:
a temperature, of an environment in physical contact the imaging system, is reduced from 20° C. to −26° C., without adjustment of the positions.
9. The digital holographic microscope of claim 1 , wherein the imaging system is portable to, and operational in, a marine environment or an arctic environment in physical contact with the imaging system, without adjustment of positions of the collimator, the mount, the first lens, the second lens, and the relay lens.
10. The digital holographic microscope of claim 1 , wherein the one or more computers compute an amplitude and/or phase of one or more electric fields at the sample.
11. The digital holographic microscope of claim 1 , wherein the sample mount, the first lens, and the second lens are positioned such that:
the portion of the sample electromagnetic radiation comprises a first straight line trajectory from the sample to the relay lens and passing through a center of the first lens,
the portion of the reference electromagnetic radiation comprises a second straight line trajectory from the sample to the relay lens and passing through a center of the second lens, and
the first straight line trajectory and the second straight line trajectory are parallel.
12. The digital holographic microscope of claim 11 , further comprising:
a sample window placed in front of the sample and defining the area of the sample irradiated by the collimated electromagnetic radiation;
a reference window placed in front of each of the one or more references to define the area of each of the references irradiated by the collimated electromagnetic radiation;
the first lens positioned at a distance f o from the sample, wherein f o is a focal distance of the first lens;
the second lens, identical to the first lens, positioned at the distance f o from the one or more references; and wherein:
an optical path length, from a center of the sample window to a center of the detector, is identical to each optical path length from each center of each reference window to the center of the detector,
an optical path length from an output of the source to the center of the sample window is identical to each optical path length from the output to each center of each reference window,
the first lens and second lens are co-mounted on a lens mount such that both the first lens and the second lens move together as a unit under thermal bending, and
a lateral thermal motion of the sample and/or relay lens relative to the remainder of the imaging system only laterally shifts the interference pattern on the detector and does not affect the image.
13. The digital holographic microscope of claim 1 , wherein:
the digital holographic microscope does not comprise a beamsplitter and/or a mirror,
the sample and the one or more references are irradiated by a single, common, and unsplit region of the collimated beam, and
a diffraction grating is not positioned between the first and second lenses and the detector.
14. The digital holographic microscope of claim 1 , wherein the system is portable without adjustment of the position of the first lens, second lens, and relay lens.
15. The digital holographic microscope of claim 1 , wherein the sample mount comprises a first mount for mounting the sample and a second mount for mounting the reference, and the reference beam incident on the detector is nominally collimated.
16. The digital holographic microscope of claim 1 , wherein:
the sample mount comprises a first chamber and a second chamber,
the sample in the first chamber interacts with the collimated electromagnetic radiation to form the sample electromagnetic radiation, and
the reference in the second chamber interacts with the collimated electromagnetic radiation to form the reference electromagnetic radiation.
17. The digital holographic microscope of claim 1 , wherein the first lens is separated from the second lens by a medium different from the first lens and the second lens.
18. The digital holographic microscope of claim 1 , wherein:
the first lens and the second lens are spaced with a spacing s,
the portion of the sample electromagnetic radiation and the portion of the reference electromagnetic radiation are directed by the relay lens onto the detector at an angle θ fr =s/f r , where f r is the focal length of the relay lens, and
θ f r <λ/2√{square root over (2)}p, where p is the pixel edge size.
19. The digital holographic microscope of claim 1 , wherein
the first lens and the second lens are spaced with a spacing s,
the first lens and the second lens each have a diameter d and a focal length f o , s/d≥1,
the relay lens has a focal lens f r ,
the first lens and the second lens are each positioned at a distance f o +f r from the relay lens, and
the relay lens is positioned at a distance f r from the detector.
20. The digital holographic microscope of claim 1 , wherein the reference beam is spread over all the pixels, thereby illuminating the full detector thus establishing the optical reference for all pixels.
21. A method of fabricating an imaging system, comprising:
providing a sample mount wherein:
a sample mounted on the sample mount interacts with collimated electromagnetic radiation to form sample electromagnetic radiation, and
one or more references mounted on the sample mount interact with the collimated electromagnetic radiation to form reference electromagnetic radiation;
providing an assembly comprising a first objective separate from a second objective; and
providing an imaging system, wherein:
at least a portion of the sample electromagnetic radiation is transmitted through the first objective to the imaging system, the imaging system and the first objective forming a real image of the sample on a sensor,
at least a portion of the reference electromagnetic radiation is transmitted through the second objective to the imaging system, forming a reference beam spread over all pixels on the sensor and
the portion of the sample electromagnetic radiation and the portion of the reference electromagnetic radiation combine at the sensor in the imaging system so as to form an interference pattern.