WO2012087875A1 - Terahertz spatial light modulator system for adaptive near-filed imaging - Google Patents

Terahertz spatial light modulator system for adaptive near-filed imaging Download PDF

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Publication number
WO2012087875A1
WO2012087875A1 PCT/US2011/065734 US2011065734W WO2012087875A1 WO 2012087875 A1 WO2012087875 A1 WO 2012087875A1 US 2011065734 W US2011065734 W US 2011065734W WO 2012087875 A1 WO2012087875 A1 WO 2012087875A1
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WIPO (PCT)
Prior art keywords
photoconductive material
terahertz
light
light source
light beam
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PCT/US2011/065734
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French (fr)
Inventor
Andrew YORK
Hari Shroff
Matthew AUBUCHON
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US Department of Health and Human Services
Office of Technology Transfer
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US Department of Health and Human Services
Office of Technology Transfer
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
    • G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
    • G01N21/3581—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light using far infrared light; using Terahertz radiation
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
    • G01J3/28—Investigating the spectrum
    • G01J3/42—Absorption spectrometry; Double beam spectrometry; Flicker spectrometry; Reflection spectrometry
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B21/00—Microscopes
    • G02B21/0004—Microscopes specially adapted for specific applications
    • G02B21/002—Scanning microscopes
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B21/00—Microscopes
    • G02B21/06—Means for illuminating specimens
    • G02B21/08—Condensers
    • G02B21/086—Condensers for transillumination only
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/0126—Opto-optical modulation, i.e. control of one light beam by another light beam, not otherwise provided for in this subclass
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/135—Liquid crystal cells structurally associated with a photoconducting or a ferro-electric layer, the properties of which can be optically or electrically varied
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2201/00—Features of devices classified in G01N21/00
    • G01N2201/06—Illumination; Optics
    • G01N2201/067—Electro-optic, magneto-optic, acousto-optic elements
    • G01N2201/0675—SLM
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/135—Liquid crystal cells structurally associated with a photoconducting or a ferro-electric layer, the properties of which can be optically or electrically varied
    • G02F1/1351—Light-absorbing or blocking layers
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F2202/00—Materials and properties
    • G02F2202/10—Materials and properties semiconductor
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F2202/00—Materials and properties
    • G02F2202/12—Materials and properties photoconductor
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F2203/00—Function characteristic
    • G02F2203/13—Function characteristic involving THZ radiation

Definitions

  • This document relates to a terahertz spatial light modulator system, and in particular to a terahertz spatial light modulator system for adaptive near-field imaging.
  • a near-field terahertz imaging system has been demonstrated to improve spatial resolution by positioning a sub-wavelength fixed aperture between the sample and either the terahertz radiation source or the terahertz radiation detector.
  • the near-field imaging system then mechanically raster scans a sample with the terahertz radiation through the fixed aperture.
  • spatial resolution is determined by the aperture size rather than the terahertz wavelength. Accordingly, the combination of micron- scale spatial resolution and terahertz frequency can match particular characteristic sizes and spectra of many important biological systems to be imaged.
  • a spatial light modulator system may include a first light source for transmitting a first light beam having a first frequency and a second light source for transmitting a second light beam having a second frequency, wherein the first frequency of the first light beam is greater than the second frequency of the second light beam.
  • a photoconductive material having opaque properties is in communication with the first light source and the second light source such that the first light beam is transmitted by the first light source through the photoconductive material to manipulate the opaque properties of the photoconductive material to define one or more transmission pathways by the first light beam through the photoconductive material that permit the second light beam to be transmitted only through one or more transmission pathways defined through the photoconductive material.
  • a computer-controlled adaptive imaging for a spatial light modulator system may include spatial light modulator system having a first light source for transmitting an optical beam, a second light source for transmitting a terahertz light beam, a filter in communication with the first light source, and a photoconductive material having opaque properties in communication with the first light source and the second light source.
  • the filter converts the optical beam into a filtered light beam to be transmitted through the photoconductive material to manipulate the opaque properties of the photoconductive material such that one or more transmission pathways are defined by the filtered optical beam, wherein the terahertz light beam is transmitted only through one or more transmission pathways defined through the photoconductive material.
  • a processor may control the filter to convert the optical beam into the filtered optical beam to define the one or more transmission pathways.
  • a sensor system may include a sensor head having a first light source for transmitting an optical beam and a second light source for transmitting a terahertz light beam.
  • a filter is in communication with the first light source and a photoconductive material having opaque properties is in communication with the first light source and the second light source.
  • the filter converts the optical beam into a filtered optical beam to be transmitted through the photoconductive material such that one or more transmission pathways are defined by the filtered optical beam.
  • the terahertz beam is transmitted only through the one or more transmission pathways defined through the photoconductive material to illuminate a sample with a detector in communication with the sample for detecting the terahertz beams radiated by the sample.
  • method for adaptive near-field imaging for a spatial light modulator system may include:
  • a spatial light modulator system having:
  • a first light source for transmitting an optical beam and a second light source for transmitting a terahertz beam
  • a filter in communication with the first light source, and a photoconductive material having opaque properties in
  • controlling the filter to convert the optical beam to a filtered optical beam such that the filtered optical beam defines one or more transmission pathways through the photoconductive material by the filtered optical beam;
  • FIG. 1 is a simplified illustration showing one embodiment of the terahertz spatial light modulator system
  • FIG. 1A is a simplified illustration of a photoconductive material used in the terahertz spatial light modulator system of FIG. 1 that forms a transmission pathway through the photoconductive material using a light source;
  • FIG. 2 is a simplified illustration showing another embodiment of the terahertz spatial light modulator system
  • FIG. 2A is a simplified illustration of the photoconductive material used in the embodiment of the terahertz spatial light modulator system of FIG. 2 that forms a plurality of transmission pathways through the photoconductive material using an optical light source;
  • FIG. 3 is a simplified illustration showing an embodiment of the terahertz spatial light modulator system directed to a sensor head arrangement
  • FIG. 4 is a simplified illustration showing an embodiment of the terahertz spatial light modulator system having a transmitter and detector arrangement
  • FIG. 5 is a flow chart illustrating a method for adaptive near-field imaging using the spatial light modulator system.
  • terahertz radiation refers to electromagnetic waves propagating at frequencies in the terahertz range. It has been known that the lowest vibration motions of many large biological molecules are in this terahertz frequency range, thereby making this frequency range suitable for studying delicate biological systems. However, the long wavelength of terahertz radiation limits the spatial resolution in diffraction-limited
  • near- field terahertz imaging systems have been developed to improve spatial resolution by positioning a sub-wavelength fixed aperture between the sample and either a terahertz radiation source or terahertz radiation detector.
  • near-field terahertz imaging systems have improved spatial resolution, such imaging systems require that the sample be mechanically scanned to completely scan the entire sample, therefore requiring moving structural components to accomplish the scanning process.
  • embodiments of the terahertz spatial light modulator system as set forth herein include particular components, properties and characteristics that address issues related to image resolution and scanning capability of a near-field terahertz imaging systems.
  • the terahertz spatial light modulator described herein includes an optical light source that manipulates the opaque properties of a photoconductive material for defining one or more transmission pathways to permit transmission of a terahertz light beam only through the one or more transmission pathways for scanning a sample with the terahertz light beam without any issues inherent to existing terahertz near-field imaging systems that require mechanical scanning of the sample. Further details of the terahertz spatial light modulator system are discussed in greater detail below.
  • the spatial light modulator system 10 may include a first light source 12 that transmits a first light beam 22 having a first frequency and a second light source 14 that transmits a second light beam 26 having a second frequency with the first frequency of the first light beam 22 being greater than the second frequency of the second light beam 26.
  • a photoconductive material 18 having opaque properties is in communication with the first light source 12 and the second light source 14 such that the first light beam 22 is transmitted onto the photoconductive material 18 to manipulate the opaque properties of the photoconductive material 18 for defining a transmission pathway 28 by the first light beam 22 to permit the second light beam 26 to be transmitted only through the
  • the photoconductive material 18 may be silicon, although in other embodiments the photoconductive material 18 may be made from regular gallium arsenide or a low temperature-grown gallium arsenide.
  • the first light source 12 may be an optical light source that transmits an optical light beam 22 in the optical frequency range
  • the second light source 14 may be a terahertz light source 14 that transmits a terahertz light beam 26 in the terahertz frequency range.
  • the photoconductive material 18 is silicon
  • the optical light beam 22 may have a wavelength of between -200 to -1100 nanometers; however, if the photoconductive material is gallium arsenide, the optical light beam 22 may have a wavelength of between -200 to -930 nanometers.
  • the terahertz light beam 26 may have a very large frequency range between 0.1 to 10 THz.
  • the optical light beam 22 may be transmitted through the photoconductive material 18 such that the opaque properties of the photoconductive material 18 are manipulated to form a particular transparent path established by optical light beam 22 by making the volume of the photoconductive material 18 surrounding the transmission pathway 28 opaque to the transmission of the terahertz light beam 26.
  • the optical light beam 22 defines the transmission pathway 28 that allows the terahertz light beam 26 to travel through only that portion of the photoconductive material 18.
  • the opaque properties of the photoconductive material 18 are manipulated by the optical light beam 22 to make portions of the photoconductive material 18 opaque to the terahertz light beam 26, rather than transparent in order to allow transmission of a terahertz light beam 26 only through the transparent pathway 28 defined by the optical light beam 22.
  • the transmission of the terahertz light beam 26 through the photoconductive material 18 is allowed by the normal transparent state of the photoconductive material 18 to light beams in the terahertz frequencies since the photoconductive material 18 is made from a material that is transparent to the terahertz light beam 26 unless manipulated by a light beam of a different frequency, such as an optical light beam, to make portions of the photoconductive material 18 opaque to the terahertz light beam 26.
  • the optical light beam 22 interacts with the photoconductive material 18, free carriers are generated which absorb and phase-shift terahertz radiation, thereby preventing transmission of the terahertz light beam 26 through that portion of the photoconductive material 18.
  • the exposure of the photoconductive material 18 to the optical light beam 22 drives the photoconductor properties of the photoconductive material 18 from being terahertz-transparent to terahertz-opaque that prevents transmission of the terahertz light beam 26 through the
  • photoconductive material 18 to revert back to a terahertz-transparent state as the lifetimes of the free carriers expire.
  • the photoconductive material 18 is silicon
  • such a photoconductor material has a long free carrier lifetime, so a low optical power source 12 may be used and still drive strong terahertz radiation opacity because the free carrier diffuse a long way in their longer lifetime which begins to blur the transmission pathway 28 created by the optical light beam 22.
  • silicon is not 100% opaque to the optical light beam 22, any sample being scanned must be protected from the transmitted optical light beam 22.
  • the photoconductive material 18 may be placed in direct contact with the sample if desired.
  • gallium arsenide such a photoconductor material has a very short free carrier lifetime, therefore a high optical power source 12 is required to drive the photoconductive material 18 into an opaque state to a terahertz light beam 26.
  • the free carriers do not diffuse very far in the carrier's short lifetime so the transmission pathways 28 defined by the optical light beam 22 are not blurred by diffusion.
  • low temperature gallium arsenide is very opaque to the optical light beam 22 so a very thin layer may be used as the photoconductive material 18 without having issues related to the optical light beam 22 leaking through the material 18.
  • gallium arsenide is not chemically inert, and therefore an inert coating may be applied to the photoconductive material 18 in order to protect the sample being scanned.
  • the photoconductive material 18 is regular gallium arsenide
  • such a photoconductor material has properties that lie between silicon and low temperature gallium arsenide, such as having medium free carrier lifetime and medium blurring of the transmission pathway 28.
  • Regular gallium arsenide is very opaque and not chemically inert.
  • the opaque properties of the photoconductive material 18 are manipulated in a manner that creates the transmission pathway 28 through the photoconductive material 18 for allowing the transmission of the terahertz light beam 26, while the photoconductive material 18 is opaque to the transmission of the terahertz light beam 26 through other portions of the photoconductive material 18 that would otherwise be transparent to the transmission of the terahertz light beam 26.
  • the size (e.g., diameter or width) and configuration (e.g., round, oval, etc) of the transmission pathway 28 may be dictated by the configuration of the optical light beam 22 transmitted through the other portions of the photoconductive material 28. As such, the size and
  • configuration terahertz light beam 26 may also dictated by the size and configuration of the optical light beam 22 that manipulates the opaque properties of the photoconductive material 18 for establishing a transparent path through the transmission pathway 28.
  • transmission pathway refers to an optical pathway that is transparent to the transmission through the photoconductive material 18 by a light beam in the terahertz frequency.
  • the spatial light modulator system 10A may include an optical light source 12 that transmits an optical light beam 22 through a light filter 16 for converting the optical light beam 22 into a filtered optical light beam 24 that may be transmitted by the light filter 16 at different or concurrent times and along one or more pathways through the photoconductive material 18. This arrangement allows one or more transmission pathways 28 to be defined through the photoconductive material 18 at a particular time and location as controlled by the light filter 16.
  • the light filter 16 may be a Light Crystal Display (LCD) for filtering the optical light beam 22 into a filtered light beam 24 using the light modulating properties of liquid crystals that fill any number of pixels arrayed within the LCD of the light filter 16
  • a terahertz light source 14 may be in communication with the photoconductive material 18 for transmitting a terahertz light beam 26 in the terahertz frequency range through the photoconductive material 18.
  • the light filter 16 may also be a Digital Micromirror Device (DMD), which functions in a similar manner as an LCD, but is reflective rather than transmissive.
  • DMD Digital Micromirror Device
  • a sample 20 may be positioned on the opposite side of the photoconductive material 18 to be selectively illuminated by the terahertz light beam 26 through one or more transmission pathways 28, for example transmission pathways 28A, 28B, and 28C, defined through the photoconductive material 18 by the filtered optical light beam 24.
  • the filtered optical light beam 24 manipulates the opaque properties of the photoconductive material 18 from being normally transparent to the transmission of the terahertz light beam 26 based on the pattern of the filtered optical light beam 24 through the photoconductive material 18.
  • terahertz spatial light modulator system 10A may further include an imaging lens 17 positioned between the light filter 16 and the
  • the LCD 16 may be used to create a spatially-variable pattern of opacity and transparency through the photoconductive material 18 by the filtered optical light beam 24 to selectively illuminate the sample 20 with the terahertz light beam 26.
  • the transmission pathways 28 may be generated at different sequences and locations through the photoconductive material 18 as controlled by the LCD 16.
  • the combination of the LCD 16 and optical light source 12 act to generate dynamic apertures by converting the optical light beam 22 into a filtered optical light beam 28 and focusing the filtered optical light beam 24 through the photoconductive material 18 to produce transmission pathways 28 at different times and/or in various locations along the photoconductive material 18.
  • any number of transmission pathways 28 may be generated by the LCD 16. This procedure for manipulating the opaque properties of the photoconductive material 18 allows the sample 20 to be completely scanned by the terahertz light beam 26 without the use of structural components to perform a raster scan or similar mechanical scanning operation since any sequence of transmission pathways 28 may be generated in order to illuminate the sample 20 with the terahertz light beam 26.
  • the terahertz spatial light modulator system 10 may include a sensor head 11 having a housing 15 defining a window 33 with a photoconductive material 18 disposed within the window 33.
  • the sensor head 11 may be in operative communication with an optical light source 12 for providing an optical light beam 22 through a fiber 32.
  • One end of the fiber 32 is disposed within a chamber 29 defined by the housing 15 for transmitting an optical light beam 22 through a light filter, such as an LCD 16.
  • the LCD 16 converts the optical light beam 22 into filtered optical light beam 24 to be transmitted through the photoconductive material 18 to define one or more respective transmission pathways 28.
  • a first imaging lens 21 may be in communication with the end of the fiber 32 for focusing the optical light beam 22 onto the LCD 16, while a second imaging lens 23 is positioned between the LCD 16 and photoconductive material 18 for focusing the filtered optical light beam 24 from the LCD 16 onto the photoconductive material 18.
  • the sensor head 11 may be in operative communication with a terahertz light source 14 that transmits a terahertz light beam 26 through an fiber 34 having one end disposed inside the chamber 29 of the housing 15 and oriented to transmit the terahertz light beam 26 through the photoconductive material 18.
  • the terahertz light source 14 may transmit a terahertz light beam 26 through third imaging lens 25 that focuses the terahertz light beam 26 to contact a beam splitter 31 for transmission of the terahertz light beam 26 through the fiber 34.
  • a fourth imaging lens 27 may be in communication with the opposite end of the fiber 34 for focusing the terahertz light beam 26 onto the photoconductive material 18 such that portion(s) of the terahertz light beam 26 may be transmitted through one or more transmission pathways 28 defined through the photoconductive material 18.
  • the LCD 16 may generate a filtered optical light beam 24 that manipulates the opacity of the
  • the LCD 16 may generate a filtered optical light beam 24 for forming any respective number of transmission pathways 28 in any sequence for completely scanning a sample 20.
  • the sensor head 11 may be positioned to illuminate the sample 20 with the terahertz light beam 26 that is transmitted through the transmission pathways 28 formed through the photoconductive material 18 by the filtered optical light beam 24.
  • the illuminated sample 20 generates a terahertz light beam 26 that may travel back through the same respective transmission pathway 28 of the photoconductive material 18 for transmission back through the fiber 34 for detection by a terahertz detector 13 that is directed by the beam splitter 31.
  • the terahertz detector 13 may be photoconductive antennae or electro-optic sampling, which would provide spectrally-resolved information.
  • bolometers or pyroelectric detectors could be used that provide calorimetric measurements.
  • an embodiment of the terahertz spatial light modulator system may include a terahertz transmitter 17 in operative communication with an optical light source 12 that transmits an optical light beam 22 that is converted into a filtered optical light beam 24 for forming one or more transmission pathways 28 (e.g., FIG. 2) through the photoconductive material 18 by causing other portions of the photoconductive material 18 to become opaque to the terahertz light beam 26.
  • a terahertz light source 14 is in operative communication with the transmitter 17 for transmitting a terahertz light beam 26 through the one or more transmission pathways 28 defined through the photoconductive material 18 by the filtered optical light beam 24.
  • the terahertz light beam 26 illuminates a sample 20.
  • the illuminated sample 20 than radiates terahertz light beams 26 that are then detected by a terahertz detector 13.
  • the sample 20 should be relatively close to the photoconductive material 18 (e.g., less than a terahertz wavelength) since a large enough gap between the photoconductive material 18 and the sample 20 can adversely affect image resolution (e.g., less than -300 microns for 1 terahertz).
  • image resolution is determined by the size of the transmission pathway 28 which can be ⁇ 1 micron or -300 times better resolution.
  • a flow chart illustrates a method for adaptive near-field imaging using the spatial light modulator system 10.
  • the method includes providing a spatial light modulator system 10 having a first light source 12 for transmitting an optical beam 22, a second light source 14 for transmitting a terahertz beam 26, a filter 16 in

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Abstract

A spatial light modulator system for adaptive near-field imaging having an optical source for transmitting an optical beam through a filter which is controlled to convert the optical light beam into a filtered optical light beam to define one or more transmission pathways through a photoconductive material is disclosed. The system further includes a terahertz light source for transmitting a terahertz beam through the one or more transmission pathways defined by the filtered optical light beam through the photoconductive material for illuminating and scanning the sample without the use of moving structural components.

Description

TERAHERTZ SPATIAL LIGHT MODULATOR SYSTEM FOR ADAPTIVE NEAR-FIELD IMAGING
RELATED APPLICATIONS
[0001] This application claims priority to U.S. Patent Application No. 61 /425,007, filed December 20, 201 0, and entitled TERAHERTZ SPATIAL LIGHT MODULATOR SYSTEM FOR ADAPTIVE NEAR-FIELD IMAGING, the entire contents of which are incorporated herein by reference.
FIELD
[0002] This document relates to a terahertz spatial light modulator system, and in particular to a terahertz spatial light modulator system for adaptive near-field imaging.
BACKGROUND
[0003] The lowest frequency vibration motions of many large biological molecules are in the terahertz frequency band. Terahertz radiation is also non-ionizing making it a good choice to study delicate biological systems like cells and tissue. However, the long wavelength of terahertz radiation limits the spatial resolution in diffraction-limited microscopes to a few hundred microns.
[0004] A near-field terahertz imaging system has been demonstrated to improve spatial resolution by positioning a sub-wavelength fixed aperture between the sample and either the terahertz radiation source or the terahertz radiation detector. The near-field imaging system then mechanically raster scans a sample with the terahertz radiation through the fixed aperture. In this type of arrangement, spatial resolution is determined by the aperture size rather than the terahertz wavelength. Accordingly, the combination of micron- scale spatial resolution and terahertz frequency can match particular characteristic sizes and spectra of many important biological systems to be imaged.
[0005] However, as noted above, existing terahertz near-field imaging systems must mechanically raster scan the sample, thereby requiring moving structural components to accomplish scanning of the sample. As such, there is a need in the art for a terahertz spatial light modulator system for adaptive near-field imaging that overcomes the limitations of prior art systems by scanning a sample without the need for a fixed aperture and/or moving structural components to accomplish the same.
SUMMARY
[0006] In an embodiment, a spatial light modulator system may include a first light source for transmitting a first light beam having a first frequency and a second light source for transmitting a second light beam having a second frequency, wherein the first frequency of the first light beam is greater than the second frequency of the second light beam. A photoconductive material having opaque properties is in communication with the first light source and the second light source such that the first light beam is transmitted by the first light source through the photoconductive material to manipulate the opaque properties of the photoconductive material to define one or more transmission pathways by the first light beam through the photoconductive material that permit the second light beam to be transmitted only through one or more transmission pathways defined through the photoconductive material.
[0007] In another embodiment, a computer-controlled adaptive imaging for a spatial light modulator system may include spatial light modulator system having a first light source for transmitting an optical beam, a second light source for transmitting a terahertz light beam, a filter in communication with the first light source, and a photoconductive material having opaque properties in communication with the first light source and the second light source. The filter converts the optical beam into a filtered light beam to be transmitted through the photoconductive material to manipulate the opaque properties of the photoconductive material such that one or more transmission pathways are defined by the filtered optical beam, wherein the terahertz light beam is transmitted only through one or more transmission pathways defined through the photoconductive material. A processor may control the filter to convert the optical beam into the filtered optical beam to define the one or more transmission pathways.
[0008] In yet another embodiment, a sensor system may include a sensor head having a first light source for transmitting an optical beam and a second light source for transmitting a terahertz light beam. A filter is in communication with the first light source and a photoconductive material having opaque properties is in communication with the first light source and the second light source. The filter converts the optical beam into a filtered optical beam to be transmitted through the photoconductive material such that one or more transmission pathways are defined by the filtered optical beam. The terahertz beam is transmitted only through the one or more transmission pathways defined through the photoconductive material to illuminate a sample with a detector in communication with the sample for detecting the terahertz beams radiated by the sample.
[0009] In one embodiment, method for adaptive near-field imaging for a spatial light modulator system may include:
providing a spatial light modulator system having:
a first light source for transmitting an optical beam and a second light source for transmitting a terahertz beam,
a filter in communication with the first light source, and a photoconductive material having opaque properties in
communication with the first light source and the second light source;
transmitting the optical beam from the first light source through the filter;
controlling the filter to convert the optical beam to a filtered optical beam such that the filtered optical beam defines one or more transmission pathways through the photoconductive material by the filtered optical beam; and
transmitting the terahertz beam from the second light source to the photoconductive material such that the terahertz beam is transmitted only through the one or more transmission pathways defined through the photoconductive material
[00010] Additional objectives, advantages and novel features will be set forth in the description which follows or will become apparent to those skilled in the art upon examination of the drawings and detailed description which follows. BRIEF DESCRIPTION OF THE DRAWINGS
[00011 ] FIG. 1 is a simplified illustration showing one embodiment of the terahertz spatial light modulator system;
[00012] FIG. 1A is a simplified illustration of a photoconductive material used in the terahertz spatial light modulator system of FIG. 1 that forms a transmission pathway through the photoconductive material using a light source;
[00013] FIG. 2 is a simplified illustration showing another embodiment of the terahertz spatial light modulator system;
[00014] FIG. 2A is a simplified illustration of the photoconductive material used in the embodiment of the terahertz spatial light modulator system of FIG. 2 that forms a plurality of transmission pathways through the photoconductive material using an optical light source;
[00015] FIG. 3 is a simplified illustration showing an embodiment of the terahertz spatial light modulator system directed to a sensor head arrangement;
[00016] FIG. 4 is a simplified illustration showing an embodiment of the terahertz spatial light modulator system having a transmitter and detector arrangement; and
[00017] FIG. 5 is a flow chart illustrating a method for adaptive near-field imaging using the spatial light modulator system.
[00018] Corresponding reference characters indicate
corresponding elements among the view of the drawings. The headings used in the figures should not be interpreted to limit the scope of the claims.
DETAILED DESCRIPTION
[00019] In physics, terahertz radiation refers to electromagnetic waves propagating at frequencies in the terahertz range. It has been known that the lowest vibration motions of many large biological molecules are in this terahertz frequency range, thereby making this frequency range suitable for studying delicate biological systems. However, the long wavelength of terahertz radiation limits the spatial resolution in diffraction-limited
microscopes to only a few hundred microns. To address this limitation, near- field terahertz imaging systems have been developed to improve spatial resolution by positioning a sub-wavelength fixed aperture between the sample and either a terahertz radiation source or terahertz radiation detector.
Although near-field terahertz imaging systems have improved spatial resolution, such imaging systems require that the sample be mechanically scanned to completely scan the entire sample, therefore requiring moving structural components to accomplish the scanning process.
[00020] As such, embodiments of the terahertz spatial light modulator system as set forth herein include particular components, properties and characteristics that address issues related to image resolution and scanning capability of a near-field terahertz imaging systems. The terahertz spatial light modulator described herein includes an optical light source that manipulates the opaque properties of a photoconductive material for defining one or more transmission pathways to permit transmission of a terahertz light beam only through the one or more transmission pathways for scanning a sample with the terahertz light beam without any issues inherent to existing terahertz near-field imaging systems that require mechanical scanning of the sample. Further details of the terahertz spatial light modulator system are discussed in greater detail below.
[00021 ] Referring to the drawings, various embodiments of the terahertz spatial light modulator system are illustrated and generally indicated as 10 in FIGS. 1-5. In general, as shown in FIG. 1 the spatial light modulator system 10 may include a first light source 12 that transmits a first light beam 22 having a first frequency and a second light source 14 that transmits a second light beam 26 having a second frequency with the first frequency of the first light beam 22 being greater than the second frequency of the second light beam 26. A photoconductive material 18 having opaque properties is in communication with the first light source 12 and the second light source 14 such that the first light beam 22 is transmitted onto the photoconductive material 18 to manipulate the opaque properties of the photoconductive material 18 for defining a transmission pathway 28 by the first light beam 22 to permit the second light beam 26 to be transmitted only through the
transmission pathway 28 defined through the photoconductive material 18 by the first light beam 22.
[00022] In an embodiment, the photoconductive material 18 may be silicon, although in other embodiments the photoconductive material 18 may be made from regular gallium arsenide or a low temperature-grown gallium arsenide.
[00023] In one embodiment, the first light source 12 may be an optical light source that transmits an optical light beam 22 in the optical frequency range, while the second light source 14 may be a terahertz light source 14 that transmits a terahertz light beam 26 in the terahertz frequency range. If the photoconductive material 18 is silicon, the optical light beam 22 may have a wavelength of between -200 to -1100 nanometers; however, if the photoconductive material is gallium arsenide, the optical light beam 22 may have a wavelength of between -200 to -930 nanometers. In an embodiment, the terahertz light beam 26 may have a very large frequency range between 0.1 to 10 THz.
[00024] In one arrangement, the optical light beam 22 may be transmitted through the photoconductive material 18 such that the opaque properties of the photoconductive material 18 are manipulated to form a particular transparent path established by optical light beam 22 by making the volume of the photoconductive material 18 surrounding the transmission pathway 28 opaque to the transmission of the terahertz light beam 26. As such, the optical light beam 22 defines the transmission pathway 28 that allows the terahertz light beam 26 to travel through only that portion of the photoconductive material 18. In other words, the opaque properties of the photoconductive material 18 are manipulated by the optical light beam 22 to make portions of the photoconductive material 18 opaque to the terahertz light beam 26, rather than transparent in order to allow transmission of a terahertz light beam 26 only through the transparent pathway 28 defined by the optical light beam 22. Otherwise, the transmission of the terahertz light beam 26 through the photoconductive material 18 is allowed by the normal transparent state of the photoconductive material 18 to light beams in the terahertz frequencies since the photoconductive material 18 is made from a material that is transparent to the terahertz light beam 26 unless manipulated by a light beam of a different frequency, such as an optical light beam, to make portions of the photoconductive material 18 opaque to the terahertz light beam 26.
[00025] When the optical light beam 22 interacts with the photoconductive material 18, free carriers are generated which absorb and phase-shift terahertz radiation, thereby preventing transmission of the terahertz light beam 26 through that portion of the photoconductive material 18. As such, the exposure of the photoconductive material 18 to the optical light beam 22 drives the photoconductor properties of the photoconductive material 18 from being terahertz-transparent to terahertz-opaque that prevents transmission of the terahertz light beam 26 through the
photoconductive material 18. However, these free carriers have a finite lifetime during which the free carriers diffuse through the photoconductive material 18, thereby blurring the opaque pattern that defines the transmission pathway 28 induced by a patterned optical light beam 22. As such,
terminating the transmission of the optical light beam 22 allows the
photoconductive material 18 to revert back to a terahertz-transparent state as the lifetimes of the free carriers expire.
[00026] When the photoconductive material 18 is silicon, such a photoconductor material has a long free carrier lifetime, so a low optical power source 12 may be used and still drive strong terahertz radiation opacity because the free carrier diffuse a long way in their longer lifetime which begins to blur the transmission pathway 28 created by the optical light beam 22. In addition, since silicon is not 100% opaque to the optical light beam 22, any sample being scanned must be protected from the transmitted optical light beam 22. Finally, since silicon is inert, the photoconductive material 18 may be placed in direct contact with the sample if desired.
[00027] When the photoconductive material 18 is a low
temperature gallium arsenide, such a photoconductor material has a very short free carrier lifetime, therefore a high optical power source 12 is required to drive the photoconductive material 18 into an opaque state to a terahertz light beam 26. However, the free carriers do not diffuse very far in the carrier's short lifetime so the transmission pathways 28 defined by the optical light beam 22 are not blurred by diffusion. As such, low temperature gallium arsenide is very opaque to the optical light beam 22 so a very thin layer may be used as the photoconductive material 18 without having issues related to the optical light beam 22 leaking through the material 18. In contrast to silicon, gallium arsenide is not chemically inert, and therefore an inert coating may be applied to the photoconductive material 18 in order to protect the sample being scanned. When the photoconductive material 18 is regular gallium arsenide, such a photoconductor material has properties that lie between silicon and low temperature gallium arsenide, such as having medium free carrier lifetime and medium blurring of the transmission pathway 28. Regular gallium arsenide is very opaque and not chemically inert.
[00028] As shown in FIGS 1 and 1 A, when the optical light beam 22 is transmitted through the photoconductive material 18, the opaque properties of the photoconductive material 18 are manipulated in a manner that creates the transmission pathway 28 through the photoconductive material 18 for allowing the transmission of the terahertz light beam 26, while the photoconductive material 18 is opaque to the transmission of the terahertz light beam 26 through other portions of the photoconductive material 18 that would otherwise be transparent to the transmission of the terahertz light beam 26. In one embodiment, the size (e.g., diameter or width) and configuration (e.g., round, oval, etc) of the transmission pathway 28 may be dictated by the configuration of the optical light beam 22 transmitted through the other portions of the photoconductive material 28. As such, the size and
configuration terahertz light beam 26 may also dictated by the size and configuration of the optical light beam 22 that manipulates the opaque properties of the photoconductive material 18 for establishing a transparent path through the transmission pathway 28. As used herein, the term
"transmission pathway" refers to an optical pathway that is transparent to the transmission through the photoconductive material 18 by a light beam in the terahertz frequency. [00029] Referring to FIG. 2, another embodiment of the terahertz spatial light modulator system, designated 10A, is illustrated. The spatial light modulator system 10A may include an optical light source 12 that transmits an optical light beam 22 through a light filter 16 for converting the optical light beam 22 into a filtered optical light beam 24 that may be transmitted by the light filter 16 at different or concurrent times and along one or more pathways through the photoconductive material 18. This arrangement allows one or more transmission pathways 28 to be defined through the photoconductive material 18 at a particular time and location as controlled by the light filter 16. In one embodiment, the light filter 16 may be a Light Crystal Display (LCD) for filtering the optical light beam 22 into a filtered light beam 24 using the light modulating properties of liquid crystals that fill any number of pixels arrayed within the LCD of the light filter 16 In addition, a terahertz light source 14 may be in communication with the photoconductive material 18 for transmitting a terahertz light beam 26 in the terahertz frequency range through the photoconductive material 18. In another embodiment, the light filter 16 may also be a Digital Micromirror Device (DMD), which functions in a similar manner as an LCD, but is reflective rather than transmissive.
[00030] As shown in FIGS. 2 and 2A, a sample 20 may be positioned on the opposite side of the photoconductive material 18 to be selectively illuminated by the terahertz light beam 26 through one or more transmission pathways 28, for example transmission pathways 28A, 28B, and 28C, defined through the photoconductive material 18 by the filtered optical light beam 24. The filtered optical light beam 24 manipulates the opaque properties of the photoconductive material 18 from being normally transparent to the transmission of the terahertz light beam 26 based on the pattern of the filtered optical light beam 24 through the photoconductive material 18. In one embodiment, terahertz spatial light modulator system 10A may further include an imaging lens 17 positioned between the light filter 16 and the
photoconductive material 18 for imaging the filtered optical light beam 24 through selected portions of the photoconductive material 18.The LCD 16 may be used to create a spatially-variable pattern of opacity and transparency through the photoconductive material 18 by the filtered optical light beam 24 to selectively illuminate the sample 20 with the terahertz light beam 26. The transmission pathways 28 may be generated at different sequences and locations through the photoconductive material 18 as controlled by the LCD 16. As such, the combination of the LCD 16 and optical light source 12 act to generate dynamic apertures by converting the optical light beam 22 into a filtered optical light beam 28 and focusing the filtered optical light beam 24 through the photoconductive material 18 to produce transmission pathways 28 at different times and/or in various locations along the photoconductive material 18. Although the present embodiment shows that three transmission pathways 28A, 28B, and 28C may be defined, any number of transmission pathways 28 may be generated by the LCD 16. This procedure for manipulating the opaque properties of the photoconductive material 18 allows the sample 20 to be completely scanned by the terahertz light beam 26 without the use of structural components to perform a raster scan or similar mechanical scanning operation since any sequence of transmission pathways 28 may be generated in order to illuminate the sample 20 with the terahertz light beam 26.
[00031 ] In one embodiment, the terahertz spatial light modulator system 10 may include a sensor head 11 having a housing 15 defining a window 33 with a photoconductive material 18 disposed within the window 33. The sensor head 11 may be in operative communication with an optical light source 12 for providing an optical light beam 22 through a fiber 32. One end of the fiber 32 is disposed within a chamber 29 defined by the housing 15 for transmitting an optical light beam 22 through a light filter, such as an LCD 16. The LCD 16 converts the optical light beam 22 into filtered optical light beam 24 to be transmitted through the photoconductive material 18 to define one or more respective transmission pathways 28. In an embodiment, a first imaging lens 21 may be in communication with the end of the fiber 32 for focusing the optical light beam 22 onto the LCD 16, while a second imaging lens 23 is positioned between the LCD 16 and photoconductive material 18 for focusing the filtered optical light beam 24 from the LCD 16 onto the photoconductive material 18.
[00032] In addition, the sensor head 11 may be in operative communication with a terahertz light source 14 that transmits a terahertz light beam 26 through an fiber 34 having one end disposed inside the chamber 29 of the housing 15 and oriented to transmit the terahertz light beam 26 through the photoconductive material 18. In an embodiment, the terahertz light source 14 may transmit a terahertz light beam 26 through third imaging lens 25 that focuses the terahertz light beam 26 to contact a beam splitter 31 for transmission of the terahertz light beam 26 through the fiber 34. A fourth imaging lens 27 may be in communication with the opposite end of the fiber 34 for focusing the terahertz light beam 26 onto the photoconductive material 18 such that portion(s) of the terahertz light beam 26 may be transmitted through one or more transmission pathways 28 defined through the photoconductive material 18. For example, the LCD 16 may generate a filtered optical light beam 24 that manipulates the opacity of the
photoconductive materials 18 to form three respective transmission pathways 28A, 28B and 28C that are transparent to the transmission of the terahertz light beam 26 to travel through the photoconductive material 18; however, the LCD 16 may generate a filtered optical light beam 24 for forming any respective number of transmission pathways 28 in any sequence for completely scanning a sample 20.
[00033] In one embodiment, the sensor head 11 may be positioned to illuminate the sample 20 with the terahertz light beam 26 that is transmitted through the transmission pathways 28 formed through the photoconductive material 18 by the filtered optical light beam 24. Once the sample 20 is illuminated by a terahertz light beam 26, the illuminated sample 20 generates a terahertz light beam 26 that may travel back through the same respective transmission pathway 28 of the photoconductive material 18 for transmission back through the fiber 34 for detection by a terahertz detector 13 that is directed by the beam splitter 31. In one embodiment, the terahertz detector 13 may be photoconductive antennae or electro-optic sampling, which would provide spectrally-resolved information. In the alternative, bolometers or pyroelectric detectors could be used that provide calorimetric measurements.
[00034] As shown in FIG. 4, an embodiment of the terahertz spatial light modulator system, designated 10B, may include a terahertz transmitter 17 in operative communication with an optical light source 12 that transmits an optical light beam 22 that is converted into a filtered optical light beam 24 for forming one or more transmission pathways 28 (e.g., FIG. 2) through the photoconductive material 18 by causing other portions of the photoconductive material 18 to become opaque to the terahertz light beam 26. A terahertz light source 14 is in operative communication with the transmitter 17 for transmitting a terahertz light beam 26 through the one or more transmission pathways 28 defined through the photoconductive material 18 by the filtered optical light beam 24. The terahertz light beam 26 illuminates a sample 20. The illuminated sample 20 than radiates terahertz light beams 26 that are then detected by a terahertz detector 13. In this arrangement, the sample 20 should be relatively close to the photoconductive material 18 (e.g., less than a terahertz wavelength) since a large enough gap between the photoconductive material 18 and the sample 20 can adversely affect image resolution (e.g., less than -300 microns for 1 terahertz). In contrast, when the distance between the photoconductive material 18 and the sample 20 is less than one terahertz wavelength, the image resolution is determined by the size of the transmission pathway 28 which can be ~1 micron or -300 times better resolution.
[00035] Referring to FIG. 5, a flow chart illustrates a method for adaptive near-field imaging using the spatial light modulator system 10. At block 1000, the method includes providing a spatial light modulator system 10 having a first light source 12 for transmitting an optical beam 22, a second light source 14 for transmitting a terahertz beam 26, a filter 16 in
communication with the first light source 12, and a photoconductive material 18 in communication with the first light source 12 and the second light source 14. At block 1002, transmitting the optical beam 22 from the first light source 12 through the filter 16. At block 1004, controlling the filter 16 to define a filtered optical light beam 24 for generating one or more transmission pathways 28 through the photoconductive material 18. At block 1006, transmitting the terahertz beam 26 from the second light source 14 to the photoconductive material 18 such that the terahertz beam 26 is transmitted through the one or more transmission pathways 28 defined through the photoconductive material 18 to illuminate a sample 20.
[00036] It should be understood from the foregoing that, while particular embodiments have been illustrated and described, various modifications can be made thereto without departing from the spirit and scope of the invention as will be apparent to those skilled in the art. Such changes and modifications are within the scope and teachings of this invention as defined in the claims appended hereto.

Claims

CLAIMS What is claimed is:
1 . A spatial light modulator system comprising:
a first light source for transmitting a first light beam having a first
frequency;
a second light source for transmitting a second light beam having a second frequency, wherein the first frequency of the first light beam is greater than the second frequency of the second light beam, and
a photoconductive material having opaque properties in communication with the first light source and the second light source such that the first light beam is transmitted by the first light source through the photoconductive material to manipulate the opaque properties of the photoconductive material to define one or more transmission pathways by the first light beam through the photoconductive material that permit the second light beam to be transmitted only through the one or more transmission pathways defined through the photoconductive material.
2. The spatial light modulator system of claim 1 , further comprising:
a filter positioned between the first light source and the
photoconductive material for converting the first light beam into a filtered first light beam to be transmitted onto the
photoconductive material for manipulating the opaque properties of the photoconductive material to define the one or more transmission pathways.
3. The spatial light modulator system of claim 2, further comprising:
a processor for controlling the filter to convert the first light beam into the filtered first light beam to define one or more transmission pathways through the photoconductive material such that the opaque properties of the photoconductive material are manipulated by the filtered first light beam.
4. The spatial light modulator system of claim 2, wherein the filter is a light crystal display.
5. The spatial light modulator system of claim 2, further comprising:
an imaging lens for imaging the first light beam onto the
photoconductive material.
6. The spatial light modulator system of claim 1 , wherein the photoconductive material is silicon, gallium arsenide, or a low temperature gallium arsenide.
7. The spatial light modulator system of claim 1 , further comprising:
a sample in communication with the photoconductive material that is illuminated by the second light beam transmitted through the one or more transmission pathways defined through the
photoconductive material by the second light beam.
8. The spatial light modulator system of claim 1 , further comprising:
a detector in communication with the photoconductive material for detecting the second light beam illuminated by the sample.
9. The spatial light modulator system of claim 1 , wherein the first light beam is an optical light beam.
10. The spatial light modulator system of claim 1 , wherein the second light beam is a terahertz light beam.
1 1 . The spatial light modulator system of claim 3, wherein a location of each
respective one or more transmission pathways defined through the
photoconductive material is determined by the processor converting the first light beam.
12. The spatial light modulator system of claim 1 , wherein the photoconductive material is normally transparent to the second light beam.
13. The spatial light modulator system of claim 12, wherein the first light beam causes the photoconductive material to become opaque to the transmission of the second light beam through the photoconductive material.
14. The spatial light modulator system of claim 1 , wherein the first light beam has a wavelength range between 200-1 1 00 nanometers.
15. The spatial light modulator system of claim 1 , wherein the second light beam has a range in frequency between 0.1 -10 terahertz.
16. A computer-controlled adaptive imaging for a spatial light modulator system comprising:
a first light source for transmitting an optical beam;
a second light source for transmitting a terahertz beam, a filter in communication with the first light source,
a photoconductive material having opaque properties in communication with the first light source and the second light source, wherein the filter converts the optical beam into a filtered optical beam to be transmitted through the photoconductive material to manipulate the opaque properties of the photoconductive material such that one or more transmission pathways are defined by the filtered optical beam, wherein the terahertz beam is transmitted through the one or more transmission pathways defined through the photoconductive material, and
a processor for controlling the filter to convert the optical beam into the filtered optical beam to define the one or more second transmission pathways.
17. The computer-controlled adaptive imaging for a spatial light modulator system of claim 16, wherein the photoconductive material is silicon, gallium arsenide, or a low temperature gallium arsenide.
18. The computer-controlled adaptive imaging for a spatial light modulator system of claim 16, further comprising:
a detector for detecting the terahertz beam transmitted through the photoconductive material.
19. The computer-controlled adaptive imaging for a spatial light modulator system of claim 16, wherein a location of the one or more transmission pathways defined through the photoconductive material is controlled by the processor.
20. The computer-controlled adaptive imaging for a spatial light modulator system of claim 16, wherein the filter is a light crystal display.
21 . A sensor system comprising:
a sensor head comprising
a first light source for transmitting an optical beam and a second light source for transmitting a terahertz beam, a filter in communication with the first light source,
a photoconductive material having opaque properties in
communication with the first light source and the second light source, wherein the filter is controlled to convert the optical beam into a filtered optical beam to be transmitted through the photoconductive material such that one or more transmission pathways are defined by the filtered light beam, wherein the terahertz beam is transmitted through one or more transmission pathways defined through the photoconductive material; and
a detector in communication with a sample for detecting the terahertz beams radiated by the sample.
22. The sensor apparatus of claim 21 , further comprising:
a beam splitter in communication with the second light source for transmitting the terahertz beam through the photoconductive material and transmitting the portion of the terahertz beam onto the detector.
23. The sensor apparatus of claim 22, further comprising:
a first lens in communication with the second light source and the beam splitter for focusing the terahertz beam onto the beam splitter.
24. The sensor apparatus of claim 22, further comprising:
a cable for transmitting the terahertz beam from the beam splitter; and a second lens in communication with the cable for focusing the
terahertz beam onto the photoconductive material in one direction and for focusing the terahertz beam back through the cable in an opposite direction.
25. The sensor apparatus of claim 21 , further comprising:
a processor in communication with the filter for controlling the filter to convert the optical beam into the filtered optical beam to define the one or more transmission pathways.
26. A method for adaptive near-field imaging for a spatial light modulator system comprising:
providing a spatial light modulator system comprising:
a first light source for transmitting an optical beam and a second light source for transmitting a terahertz beam,
a filter in communication with the first light source, and a photoconductive material in communication with the first light source and the second light source;
transmitting the optical beam from the first light source through the filter;
controlling the filter to convert the optical beam to a filtered optical beam such that the filtered optical beam defines one or more transmission pathways through the photoconductive material by the filtered optical beam; and
transmitting the terahertz beam from the second light source to the photoconductive material such that the terahertz beam is transmitted through the one or more transmission pathways defined through the photoconductive material.
27. The method for adaptive near-field imaging of claim 26, further comprising:
providing a sample for illumination by the portion of the terahertz beam transmitted through the one or more transmission pathways defined through the photoconductive material.
28. The method for adaptive near-field imaging of claim 27, further comprising:
providing a detector for detecting the portion of the terahertz beam that illuminates the sample. The method for adaptive near-field imaging of claim 27, further comprising: controlling the liquid crystal display such that the sample is illuminated by the terahertz beam transmitted through the one or more transmission pathways defined through the photoconductive material along a predetermined scanning path, wherein the predetermined scanning path may be a single transmission pathway or multiple transmission pathways.
PCT/US2011/065734 2010-12-20 2011-12-19 Terahertz spatial light modulator system for adaptive near-filed imaging Ceased WO2012087875A1 (en)

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