# US 10,768,339 B1 · Imaging hidden objects

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- Number: US 10,768,339 B1
- Document ID: US10768339B1
- Status: Granted
- Kind: B1
- Application number: 15/659,517
- Filed: 2017-07-25
- Granted: 2020-09-08
- Earliest claimed: 2017-07-25
- Assignees: Southern Methodist University
- Applicants: Southern Methodist University
- Inventors: Marc P. Christensen; Prasanna Rangarajan
- Web page: https://patentgrep.com/patent/US10768339B1

## CPC

- G01V 8/12: using one transmitter and one receiver
- G01V 8/14: using reflectors
- G01V 8/20: using multiple transmitters or receivers
- G03H 1/0005: {Adaptation of holography to specific applications (holographic optical element G02B5/32; holographic scanner G02B26/106; recognition using holographic mask G06V10/88; holographic memories G11B7/0065, G11C13/042)}
- G03H 1/041: {Optical element in the object space affecting the object beam, not otherwise provided for}
- G03H 1/0443: {Digital holography, i.e. recording holograms with digital recording means (holobject computation G03H1/0866)}
- G03H 1/0465: {Particular recording light; Beam shape or geometry (G03H1/06 takes precedence)}
- G06V 10/145: Illumination specially adapted for pattern recognition, e.g. using gratings
- G06V 10/147: Details of sensors, e.g. sensor lenses (fingerprint or palmprint sensors G06V40/13; vascular sensors G06V40/145; eye sensors G06V40/19)
- G06V 10/88: Image or video recognition using optical means, e.g. reference filters, holographic masks, frequency domain filters or spatial domain filters
- G06V 10/89: {using frequency domain filters, e.g. Fourier masks implemented on spatial light modulators}
- G06V 20/52: Surveillance or monitoring of activities, e.g. for recognising suspicious objects (recognising microscopic objects G06V20/69)
- G03H 2001/0083: {for restoring distorted objects, e.g. restoring objects through scattering media}
- G03H 2001/0441: {Formation of interference pattern, not otherwise provided for}
- G03H 2001/0458: {Temporal or spatial phase shifting, e.g. parallel phase shifting method}
- G03H 2001/0463: {Frequency heterodyne, i.e. one beam is frequency shifted}
- G03H 2001/0469: {Object light being reflected by the object}
- G03H 2223/14: Diffuser, e.g. lens array, random phase mask
- G01V: GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS (means for indicating the location of accidentally buried, e.g. snow-buried, persons A63B29/02)
- G03H: HOLOGRAPHIC PROCESSES OR APPARATUS (holograms, e.g. point holograms, used as ordinary optical elements G02B5/32; producing stereoscopic or other three-dimensional effects G02B30/00; diffraction-grating systems G02B27/44; systems using moiré fringes G02B27/60; optical logic elements G02F3/00; stereo-photography G03B35/00; photosensitive materials or processes for photographic purposes G03C; {stereo-photographic or similar processes G03C9/00}; apparatus for processing exposed photographic materials G03D; analogue computers performing mathematical operations with the aid of optical elements G06E3/00; authentication by radiation, of concealed information carried by holograms or diffraction gratings G06K19/16; holographic storage G11B7/0065, G11C13/04; {stereoscopic or other three dimensional effects in television systems H04N13/00})
- G06V: IMAGE OR VIDEO RECOGNITION OR UNDERSTANDING

## Abstract

The present disclosure describes an imaging system, method, and apparatus for identifying a latent image of a hidden object. A light source generates a first beam of narrow-band light and a second beam of narrow-band light that has temporal fluctuations correlated with the first beam. A frequency modulator shifts a temporal frequency of at least one of the first beam or the second beam. The first beam is directed towards a first scattering surface and the second beam is directed towards a second scattering surface. The first scattering surface scatters the first beam to a scattered light that illuminates a hidden object. The hidden object reflects at least a portion of the scattered light towards the second scattering surface, the reflected light interferes with the second beam and produces an interference pattern on the second scattering surface. A lock-in camera detects an irradiance of the interference pattern, monitors temporal variations of the irradiance caused by the temporal frequency shift introduced by the frequency modulator, and identifies a complex-valued light field that represents information of the hidden object based on the temporal variations of the irradiance.

## Claims

### Claim 1

An imaging system for identifying information of an object hidden from view, the imaging system comprises:
a light source that generates a first beam of narrow-band light and a second beam of narrow-band light that has temporal fluctuations correlated with the first beam;
a frequency modulator positioned along a propagation direction of at least one of the first beam or the second beam that shifts a temporal frequency of at least one of the first beam or the second beam, the first beam is directed towards a first scattering surface and the second beam is directed towards a second scattering surface, wherein both the first scattering surface and the second scattering surface have a surface roughness greater than a wavelength of light, and wherein the first scattering surface scatters the first beam to a scattered light that illuminates a hidden object, the hidden object reflects at least a portion of the scattered light towards the second scattering surface, the at least a portion of the scattered light interferes with the second beam and produces an interference pattern on the second scattering surface; and
a lock-in camera that detects an irradiance of the interference pattern, monitors temporal variations of the irradiance caused by the temporal frequency shift introduced by the frequency modulator, and identifies a complex-valued light field that represents information of the hidden object based on the temporal variations of the irradiance.

### Claim 2 (depends on 1)

The imaging system of claim 1, wherein the frequency modulator is an acousto-optic modulator, an electro-optic modulator, or a moving mirror.

### Claim 3 (depends on 1)

The imaging system of claim 1, wherein the lock-in camera includes a single-pixel detector or a focal array detector that performs synchronous demodulation of the temporal variations of the irradiance.

### Claim 4 (depends on 1)

The imaging system of claim 1, wherein the first scattering surface at least partially overlaps with the second scattering surface.

### Claim 5 (depends on 1)

The imaging system of claim 1, wherein the light source includes a narrow-band light source that emits narrow-band light and a first beam splitter that splits the narrow-band light to the first beam and the second beam.

### Claim 6 (depends on 1)

The imaging system of claim 1, wherein the narrow-band light is coherent and a linewidth of the narrow-band light is less than or equal to one nanometer.

### Claim 7 (depends on 1)

The imaging system of claim 1, wherein the light source is a laser source, one or more light emitting diodes, or a broadband light source with a narrow-band light filter.

### Claim 8 (depends on 1)

The imaging system of claim 1, wherein the narrow-band light has a frequency range in a visible portion of an electromagnetic spectrum, an infrared, an ultraviolet, or a millimeter wave spectrum.

### Claim 9 (depends on 1)

The imaging system of claim 1, wherein the complex-valued light field represents a hologram of the hidden object, and the lock-in camera further performs numerical approximation to identify the hologram of the hidden object.

### Claim 10 (depends on 1)

The imaging system of claim 1, wherein the lock-in camera further performs numerical approximation to identify an image of the hidden object based on a magnitude component of the complex-valued light field.

### Claim 11 (depends on 1)

The imaging system of claim 1, wherein the lock-in camera further performs numerical approximation to identify a geometry of the hidden object based on a phase component of the complex-valued light field.

### Claim 12 (depends on 1)

The imaging system of claim 1, wherein the lock-in camera further performs a field propagation, a Fourier transform, or a numerical approximation of the complex-valued light field.

### Claim 13

An method for identifying information of an object hidden from view, comprising:
generating a first beam of narrow-band light to illuminate on a first scattering surface;
generating a second beam of narrow-band light to illuminate on a second scattering surface, the second beam having temporal fluctuations correlated with the first beam;
shifting a temporal frequency of at least one of the first beam or the second beam;
wherein the first beam is directed towards a first scattering surface and the second beam is directed towards a second scattering surface, and wherein both the first scattering surface and the second scattering surface have a surface roughness greater than a wavelength of light, and wherein the first scattering surface scatters the first beam to a scattered light that illuminates a hidden object, the hidden object reflects at least a portion of the scattered light towards the second scattering surface, the at least a portion of the scattered light interferes with the second beam and produces an interference pattern on the second scattering surface;
detecting an irradiance of the interference pattern;
monitoring temporal variations of the irradiance caused by the temporal frequency shift; and
identifying a complex-valued light field that represents information of the hidden object based on the temporal variations of the irradiance.

### Claim 14 (depends on 13)

The method of claim 13, further comprises performing synchronous demodulation of the detected temporal variations of the irradiance.

### Claim 15 (depends on 13)

The method of claim 13, wherein the narrow-band light is coherent and a linewidth of the narrow-band light is less than or equal to one nanometer.

### Claim 16 (depends on 13)

The method of claim 13, wherein the narrow-band light has a frequency range in a visible portion of an electromagnetic spectrum, an infrared, an ultraviolet, or a millimeter wave spectrum.

### Claim 17 (depends on 13)

The method of claim 13, further comprises performing numerical approximation to identify a hologram of the hidden object based on the complex-valued light field.

### Claim 18 (depends on 13)

The method of claim 13, further comprises performing numerical approximation to identify an image of the hidden object based on a magnitude component of the complex-valued light field.

### Claim 19 (depends on 13)

The method of claim 13, further comprises performing numerical approximation to identify a geometry of the hidden object based on a phase component of the complex-valued light field.

### Claim 20 (depends on 13)

The method of claim 13, further comprises performing a field propagation, a Fourier transform, or a numerical approximation of the complex-valued light field.