Abstract
An apparatus has a transducer with a storage phosphor that is chargeable to emit light of a first wavelength in response to an excitation light of a second wavelength from an object scene, wherein the second wavelength is longer than the first wavelength. A digital light sensor is disposed to accumulate energy from the emitted light of the transducer and to generate a signal according to the accumulated energy. A charging illumination source is configured to direct a pulsed charging illumination of a third wavelength, shorter than the first wavelength, to the storage phosphor. A control logic processor is in signal communication with the digital light sensor and the charging illumination source and controls synchronization of the timing of pulsed charging illumination and energy acquisition and readout of the digital light sensor.
Claims
1. An apparatus comprising: a) a transducer comprising a storage phosphor that is chargeable to emit light of a first wavelength in response to an excitation light of a second wavelength from an object scene, wherein the second wavelength is longer than the first wavelength; b) a digital light sensor disposed to accumulate energy from the emitted light of the transducer and to generate a signal according to the accumulated energy; c) a charging illumination source that is configured to direct a pulsed charging illumination of a third wavelength, shorter than the first wavelength, to the storage phosphor; and d) a control logic processor that is in signal communication with the digital light sensor and the charging illumination source and that controls synchronization of the timing of pulsed charging illumination and energy acquisition and readout of the digital light sensor.
2. The apparatus of claim 1 wherein the first wavelength has the range from 400 to 1000 nm, wherein the second wavelength is longer than 1000 nm, and wherein the third wavelength is shorter than 700 nm.
3. The apparatus of claim 1 further comprising an external gating device in signal communication with the control logic processor for synchronization timing.
4. The apparatus of claim 1 further comprising an optical filter disposed to block light of the first wavelength from the object scene.
5. The apparatus of claim 4 wherein the optical filter is part of the transducer.
6. The apparatus of claim 1 further comprising a wavelength band selector for selectively removing the transducer from between the object scene and the digital light sensor.
7. The apparatus of claim 1 further comprising a dichroic mirror that is disposed to reflect the charging illumination of the third wavelength toward the storage phosphor and to transmit emitted light of the first wavelength.
8. The apparatus of claim 1 further comprising a dichroic mirror that is disposed to transmit the charging illumination of the third wavelength toward the storage phosphor and to reflect emitted light of the first wavelength toward the digital light sensor.
9. The apparatus of claim 1 further comprising a dichroic mirror that is disposed to transmit the charging illumination of the third wavelength toward the storage phosphor and to reflect light of the second wavelength toward the digital light sensor.
10. The apparatus of claim 1 wherein the phosphor layer is coated onto the digital light sensor.
11. The apparatus of claim 1 further comprising a temperature control device coupled to the transducer.
12. The apparatus of claim 1 further comprising a temperature control device coupled to the transducer and to the digital light sensor.
13. The apparatus of claim 11 wherein the temperature control device is a thermoelectric cooler.
14. The apparatus of claim 1 wherein the digital light sensor and control logic processor are within a housing and wherein the transducer is external to the housing.
15. The apparatus of claim 1 wherein the digital light sensor is a charge-coupled device.
16. An apparatus for infrared imaging comprising: a) a transducer comprising a storage phosphor that is chargeable to emit light of a first wavelength in response to an excitation light of a second wavelength from an object scene, wherein the second wavelength is longer than the first wavelength; b) a pattern forming optic that directs light from the object scene to the transducer; c) an image forming optic that directs emitted light from the transducer to a digital light sensor; d) the digital light sensor disposed to accumulate energy from the emitted light of the transducer and to generate a signal according to the accumulated energy; e) a charging illumination source that is configured to direct a pulsed charging illumination of a third wavelength, shorter than the first wavelength, to the storage phosphor; f) a control logic processor that is in signal communication with the digital light sensor to obtain the generated signal and with the charging illumination source, wherein the control logic processor is programmed with instructions to control synchronization of the timing of pulsed charging illumination and energy acquisition and readout from the digital light sensor; and g) a display in signal communication with the control logic processor for display of the acquired emitted light content from the digital light sensor.
17. A method for infrared imaging comprising: a) forming a transducer comprising a storage phosphor that is chargeable to emit light of a first wavelength in response to an excitation light of a second wavelength from an object scene, wherein the second wavelength is longer than the first wavelength; b) disposing a digital light sensor in the path of the emitted light of the transducer; c) repeating a process of: (i) gating the digital light sensor, during a charging period, to momentarily suspend energy accumulation; (ii) during the charging period, directing a pulsed charging illumination to the storage phosphor, wherein the charging illumination is of a third wavelength, shorter than the first wavelength; and (iii) suspending the charging period and accumulating energy from the emitted light of the transducer, during a photocharge acquisition period; and d) obtaining a readout signal generated by the digital light sensor according to the accumulated energy.
18. The method of claim 17 further comprising displaying an image formed according to the accumulated energy from the digital light sensor.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] For a fuller understanding of the nature and objects of the invention, reference should be made to the following detailed description, taken in connection with the accompanying drawings, in which:
[0031] FIG. 1A shows a schematic of a digital infrared detection apparatus according to an embodiment of the present disclosure wherein the digital light sensor is gated directly;
[0032] FIG. 1B shows a schematic of a digital infrared detection apparatus according to another embodiment of the present disclosure wherein the digital light sensor is gated indirectly;
[0033] FIG. 2A shows a schematic of a digital infrared detection apparatus according to still another embodiment of the present disclosure that includes an optical filter, discrete from the phosphor layer, for blocking non-infrared light;
[0034] FIG. 2B shows a schematic of a digital infrared detection apparatus according to still another embodiment of the present disclosure that includes an optical filter, integrated with the phosphor layer, for blocking non-infrared light;
[0035] FIG. 2C shows a schematic of a digital infrared detection apparatus according to still another embodiment of the present disclosure that includes a wavelength band selector for extended range detection shown configured for infrared detection;
[0036] FIG. 2D shows a schematic of a digital infrared detection apparatus according to still another embodiment of the present disclosure that includes a wavelength band selector for extended range detection shown configured for non-infrared detection;
[0037] FIG. 3A shows a schematic of a digital infrared detection apparatus according to still another embodiment of the present disclosure that includes a dichroic cold mirror for reflecting optical charging illumination towards the phosphor layer while transmitting the emitted light from the phosphor layer towards the digital light sensor;
[0038] FIG. 3B shows a schematic of a digital infrared detection apparatus according to still another embodiment of the present disclosure that includes a dichroic cold mirror for reflecting optical charging illumination towards the phosphor layer while transmitting the infrared light pattern towards the phosphor layer;
[0039] FIG. 3C shows a schematic of a digital infrared detection apparatus according to still another embodiment of the present disclosure that includes a dichroic hot mirror for transmitting optical charging illumination towards the phosphor layer while reflecting the emitted light from the phosphor layer towards the digital light sensor;
[0040] FIG. 3D shows a schematic of a digital infrared detection apparatus according to still another embodiment of the present disclosure that includes a dichroic hot mirror for transmitting optical charging illumination towards the phosphor layer while reflecting the infrared light pattern towards the phosphor layer;
[0041] FIG. 4 shows a schematic of a digital infrared detection apparatus according to still another embodiment of the present disclosure wherein the phosphor layer is directly coated over the digital light sensor;
[0042] FIG. 5 shows a schematic of a digital infrared detection apparatus according to still another embodiment of the present disclosure that includes an optical filter for blocking non-infrared light wherein the phosphor layer is directly coated over the digital light sensor;
[0043] FIG. 6A shows a schematic of a digital infrared detection apparatus according to still another embodiment of the present disclosure that includes a temperature control device for controlling the temperature of the phosphor layer;
[0044] FIG. 6B shows a schematic of a digital infrared detection apparatus according to still another embodiment of the present disclosure that includes a temperature control device for controlling the temperature of both the phosphor layer and the digital light sensor wherein the phosphor layer is directly coated over the sensor;
[0045] FIG. 7 shows a schematic of a digital infrared detection apparatus according to still another embodiment of the present disclosure whereby the phosphor layer is an external component of the apparatus;
[0046] FIG. 8 shows a timing diagram according to a method of the present disclosure for image capture; and
[0047] FIG. 9 shows a timing diagram according to a method of the present disclosure for video capture.
DETAILED DESCRIPTION OF THE INVENTION
[0048] The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention. The following is a detailed description of the preferred embodiments of the invention, reference being made to the drawings in which the same reference numerals identify the same elements of structure in each of the several figures.
[0049] Figures shown and described herein are provided in order to illustrate key principles of operation and component relationships along their respective optical paths according to the present disclosure and are not drawn with intent to show actual size or scale. Some exaggeration may be necessary in order to emphasize basic structural relationships or principles of operation. Some conventional components that would be needed for implementation of the described embodiments, such as various types of optical mounts, for example, are not shown in the drawings in order to simplify description of the invention itself. In the drawings and text that follow, like components are designated with like reference numerals, and similar descriptions concerning components and arrangement or interaction of components already described are omitted. Where they are used, the terms “first”, “second”, and so on, do not denote any ordinal or priority relation, but are simply used to more clearly distinguish one element from another.
[0050] In the context of the present disclosure, an optically-chargeable phosphor is the type of storage phosphor described previously in the background section that is charged with light energy from a higher energy (shorter wavelength) charging light source, in order to allow subsequent emission at lower energy (longer wavelength) light levels, upon receiving light energy from an excitation light source that is also at lower energy than the charging light source.
[0051] In the context of the present disclosure, the term “optics” is used generally to refer to lenses and other refractive, diffractive, and reflective components or apertures used for shaping and orienting a light beam. An individual component of this type is termed an optic.
[0052] In the context of the present disclosure, the general terms “wavelength” and “wavelength band” may be used equivalently to refer to light wavelengths within the specified spectral range.
[0053] Applicants have recognized a need for an apparatus for digital infrared detection based on an optically-chargeable phosphor layer and that provides an effective countermeasure against the discharging of the optically-chargeable phosphor layer.
[0054] Referring to FIG. 1A, an overall design of an embodiment of an apparatus of the present disclosure has a digital light sensor 10, for example an interline-transfer charge-coupled device sensor, a frame-transfer charge-coupled device (CCD) sensor, a full-frame charge-coupled device sensor, or a complementary metal-oxide-semiconductor (CMOS) sensor. A transducer 22 has an optically-chargeable phosphor layer 20 for generating, in response to incident light of infrared wavelengths outside the sensitivity range of light sensor 10, visible or NIR light energy that lies within the sensitivity range of digital light sensor 10. In various embodiments, the emitted light is shorter in wavelength than the incident excitation light. According to an embodiment of the present disclosure, emitted light from transducer 22 is in the range from 400 to 1000 nm and the incident excitation light from the object scene is longer than 1000 nm. A pulsed charging illumination source 30 is provided for repetitively recharging phosphor layer 20 in synchronization with image capture timing. The goal of gating is to synchronize charging and detection so that sensor 10 detects only the desired image content that results from incident infrared light from object scene A and ignores the charging energy from illumination source 30 as well as any intrinsic phosphorescence or autofluorescence energy simulated solely by the optical charging illumination and not emitted in response to the incident infrared light.
[0055] Gating synchronization, a function controlled through a control logic processor 60, operates as follows: during pulse intervals when phosphor layer 20 is being charged, image energy is not obtained by digital light sensor 10. During alternate pulse intervals when phosphor layer is not being charged, digital light sensor 10 is gated to accumulate or capture image content resulting from infrared light that is incident on phosphor layer 20. For methods that are based on integrating multiple exposures, one during each pulse interval, image noise can be significantly reduced, since there is only a single readout of the light sensor 10, rather than multiple readout events.
[0056] The gating of digital light sensor 10 may be carried out in a number of ways familiar to those skilled in the art. One gating approach uses direct control of the sensor, for example in the case of an interline-transfer charge coupled device (CCD), by electronically controlling the charge-drain facility on the CCD component as described by Mitchell et al. in “Measurement of nanosecond time-resolved fluorescence with a directly gated interline CCD camera”, J. Microscopy, 206, 233-238 (2002). Using sensor gating, digital light sensor 10 accumulates the photocharge generated corresponding to the visible or NIR light pattern that is present only during those intervals when pulsed illumination source 30 is not charging phosphor layer 20, and further discards the photocharge generated during those intervals when pulsed illumination source 30 is charging phosphor layer 20.
[0057] Alternatively, the gating of digital light sensor 10 may be carried out indirectly by other means external to sensor 10 and known in the art. External gating mechanisms can include, for example a mechanical shutter or chopper wheel, a movable mirror or digital micromirror device such as a digital light processor (DLP) from Texas Instruments, Dallas, Tex., a liquid crystal device, or an image intensifier such as a proximity-focused intensifier that incorporates a microchannel plate electron multiplier that can be gated by pulsing the voltage between the light-sensitive photocathode and the front face of the microchannel plate, or alternatively by switching the voltage across the microchannel. Using such an external mechanism, digital light sensor 10 accumulates the photocharge that has been generated corresponding to the visible or NIR light pattern that is present only during those intervals when pulsed illumination source 30 is not charging phosphor layer 20. When pulsed illumination source 30 is directed to phosphor layer 20 for charging, image content is not available to sensor 10. Furthermore, the gating of digital light sensor 10 may include a delay for compensating some interval of afterglow of phosphor layer 20 immediately following charging. Afterglow can occur, for example, due to intrinsic phosphorescence or autofluorescence simulated only by the optical charging illumination and not in response to incident infrared illumination. Afterglow effects can tend to diminish or contaminate the desired signal content, providing unwanted background artifacts. Delay can help to reduce effects of intrinsic phosphorescence decay.
[0058] Illumination source 30 used for charging can be any of a number of types of light source known in the art, such as a light emitting diode, laser, laser diode, or lamp, for example. Illumination source 30 may be pulsed directly, for example by an electrical circuit, or pulsed by external mechanisms, such as by a mechanical shutter or chopper. Furthermore, illumination source 30 may have any suitable physical configuration, for example a spotlight or ringlight. Illumination source 30 may include a number of illuminating elements; and may have any suitable physical arrangement and supporting optical components for charging phosphor layer 20 during a charging interval. Illumination source 30 generates light in the ultraviolet (UV) or visible light, in the wavelength range below about 700 nm. Charging illumination for a particular configuration can be dependent on the phosphor that is used.
[0059] FIG. 1A shows a schematic of a digital infrared detection apparatus 1000 according to an embodiment of the present disclosure. Scene A provides infrared (IR) light, represented by longer wavy arrows. For example, the infrared light provided by scene A may be the result of emission, reflection, transmission, scattering, or diffraction. The infrared light provided by scene A is projected onto phosphor layer 20 as a pattern B. A pattern forming optic 40 is shown for forming infrared pattern B.
[0060] In subsequent schematics of the various embodiments, the pattern forming optic 40 is shown as a single lens that simply reverses the image of scene A. More generally, any pattern forming optic as known in the art, such as monolithic or multi-element lenses, mirrors, plenoptic arrays, prisms, diffraction gratings, interferometers, and combinations thereof, may be used, and the projected infrared pattern may be the result of light conditioning by any such pattern forming optic. Furthermore, certain applications, for example beam visualization, may not require a pattern forming optic. Illumination source 30 is repetitively pulsed for repetitively recharging phosphor layer 20, using timing described in more detail subsequently.
[0061] In FIG. 1A, illumination source 30 is shown positioned to illuminate the side of phosphor layer 20 from an oblique angle, with the charging illumination incident opposite to the side on which the infrared light is incident. Alternatively, illumination source 30 may be positioned to illuminate the same side of phosphor layer 20 on which the infrared light is incident, or illumination source 30 may be positioned to simultaneously illuminate both sides of phosphor layer 20 during the charging interval.
[0062] When charged, phosphor layer 20 emits a pattern of visible or NIR light, represented by a shorter wavy sinusoidal curve, that corresponds to the pattern of infrared light that is incident upon phosphor layer 20 from object scene A. An image forming optic 50 forms an image C of the visible or NIR light emitted by phosphor layer 20, which is in the object space of image forming optic 50, onto digital light sensor 10. Digital light sensor 10 may be any digital light sensor known in the art, for example a charge-coupled device (CCD) sensor, a complementary metal-oxide-semiconductor (CMOS) sensor, or other sensor that is capable of detecting the visible or NIR light emitted from phosphor layer 20. A control logic processor 60 is in signal communication with digital light sensor 10. Control logic processor 60 triggers the image or video capture by digital light sensor 10, triggers the repetitive pulsing of illumination source 30, repetitively directly gating digital light sensor 10 in synchronization with repetitively pulsed illumination source 30 during capture, and delivers digital image or video data D to a display 70 that is in signal communication with control logic processor 60. Alternatively the image or video capture by digital light sensor 10 may be externally triggered, for example by one or more events related to scene A. Also alternatively, control logic processor 60 may be triggered by illumination source 30, for example by a direct electrical signal from illumination source 30 or by indirect detection using a photosensor (not shown). Also the digital image or video data may be saved, printed, displayed, stored, or transmitted by control logic processor 60 to an external processor or storage device.
[0063] Control logic processor 60 can be any of a number of types of logic processing devices including, for example, a microprocessor, dedicated processor, or computer system, including a networked computer device. Control logic processor 60 is programmed with instructions to control and coordinate the timing of transducer charging, signal acquisition, and readout, and to provide at least some measure of image processing for preparation and display or for transmission or storage of the acquired image data.
[0064] FIG. 1B shows a schematic of a digital infrared detection apparatus 1010 according to another embodiment of the present disclosure. Apparatus 1010 is similar to apparatus 1000 shown in FIG. 1A except that, instead of directly gating digital light sensor 10, control logic processor 60 indirectly gates digital light sensor 10 by means of an external synchronizer such as an indirect gating device 80, for example a mechanical shutter, a chopper wheel, a movable mirror, a digital micromirror device, a liquid crystal device, or an image intensifier.
[0065] FIG. 2A shows a schematic of a digital infrared detection apparatus 1020 according to another embodiment of the present disclosure. Scene E provides infrared (IR) light. Scene E also provides non-infrared light within the sensitivity range of digital light sensor 10, represented by the shorter wavy sinusoidal curve, such as UV, visible, or NIR light, for example. If this light were allowed to reach, and fall within the sensitivity range of, digital light sensor 10, the non-infrared light could add unwanted background, and hence contaminate, the desired infrared image signal. Furthermore, if the non-infrared light were allowed to reach phosphor layer 20, portions of the non-infrared light could charge phosphor layer 20 in an undesirable way. For example, the light could charge phosphor layer 20 in a non-uniform manner that may degrade the image quality of the infrared image. Apparatus 1020 is similar to apparatus 1000 shown in FIG. 1A except that an optical filter 90, discrete from phosphor layer 20, is included for substantially transmitting infrared light and substantially blocking non-infrared light. FIG. 2A shows filter 90 substantially reflecting the non-infrared light. Alternatively, filter 90 may substantially absorb, or partially absorb and partially reflect, the non-infrared light. FIG. 2A shows filter 90 positioned immediately in front of phosphor layer 20 so as to block the non-infrared light from being incident upon phosphor layer 20 and, because phosphor layer 20 may be at least partially transparent to the non-infrared light, from also being incident upon digital light sensor 10. Alternatively, filter 90 may be positioned anywhere between scene E and phosphor layer 20, or furthermore, anywhere in front of digital light sensor 10.
[0066] FIG. 2B shows a schematic of a digital infrared detection apparatus 1030 according to another embodiment of the present disclosure. Apparatus 1030 is similar to apparatus 1020 shown in FIG. 2A with optical filter 95 additionally integrated with phosphor layer 20. For example, phosphor layer 20 can be coated onto one side of a transparent substrate, with filter 95 coated onto the other side.
[0067] Alternatively, phosphor layer 20 and filter 95 may each be coated on individual substrates, and the two substrates cemented together. Integration of filter 95 with phosphor layer 20 as part of transducer 22 may provide a compact and efficient use of space.
[0068] FIGS. 2C and 2D show schematics of a digital infrared detection apparatus 1040 according to another embodiment of the present disclosure. Apparatus 1040 is similar to apparatus 1030 shown in FIG. 2B with phosphor layer 20, with integrated filter 95, mounted in a wavelength band selector 100. The wavelength band selector may have the form of a rotatable wheel that includes a zone for infrared detection, in which phosphor layer 20 is mounted, and at least one additional zone for non-infrared detection, for example an empty aperture 102, as shown in FIGS. 2C and 2D. Alternatively wavelength band selector 100 may have the form of a translatable panel, or generally any mechanism capable of exchanging between a first configuration with phosphor layer 20 inserted into the detection optical path for infrared detection and a second configuration where the detection optical path is capable of non-infrared detection, such as visible light sensing for example. Wavelength band selector 100 may be controlled by control logic processor 60, or alternatively may be independently controlled.
[0069] FIG. 2C shows apparatus 1040 configured for infrared detection with pattern forming optic 40 forming infrared pattern B onto phosphor layer 20, which is in the object space of image forming optic 50 so that image C of the emission of phosphor layer 20 is formed and delivered as digital image or video data D. FIG. 2D shows apparatus 1040 configured for non-infrared detection with pattern forming optic 40 forming non-infrared pattern F into aperture 102, which is also in the object space of image forming optic 50, so that image G of non-infrared pattern F is formed and delivered as digital image or video data H.
[0070] FIGS. 3A, 3B, 3C, and 3D show schematics of digital infrared detection apparatus 1050, 1060, 1070, and 1080, respectively, that make use of various dichroic mirrors, also known as cold mirrors and hot mirrors, for evenly directing charging illumination towards phosphor layer 20 according to further embodiments of the present disclosure.
[0071] FIG. 3A shows a schematic of apparatus 1050 which is similar to apparatus 1000 shown in FIG. 1A except that a dichroic cold mirror 110, that transmits infrared light and reflects light having wavelengths shorter than infrared, is included between phosphor layer 20 and image forming optic 50. Illumination source 30 in this configuration, through mirror 110, directs charging illumination at a normal to phosphor layer 20. Charging illumination is from the side of phosphor layer 20 that faces towards digital light sensor 10.
[0072] FIG. 3B shows a schematic of apparatus 1060 which is similar to apparatus 1050 shown in FIG. 3A except that dichroic cold mirror 110 is spatially disposed between pattern forming optic 40 and phosphor layer 20. The charging illumination from illumination source 30 reflects from dichroic cold mirror 110 to illuminate phosphor layer 20 at a normal, along the side opposite digital light sensor 10.
[0073] FIG. 3C shows a schematic of apparatus 1070 which is similar to apparatus 1050 shown in FIG. 3A but has a different mirror configuration for charging illumination. Instead of a dichroic cold mirror 110, a dichroic hot mirror 112 that reflects infrared light and transmits light having wavelengths shorter than infrared, is used. Mirror 112 transmits the charging illumination from illumination source 30 to illuminate the rear side of phosphor layer 20 at a normal.
[0074] FIG. 3D shows a schematic of apparatus 1080 which is similar to apparatus 1070 shown in FIG. 3C. In apparatus 1080, however, dichroic hot mirror 112 is disposed so that the charging illumination from illumination source 30 normally illuminates the front side of phosphor layer 20.
[0075] FIG. 4 shows a schematic of digital infrared detection apparatus 1090 according to another embodiment of the present disclosure. Apparatus 1090 is similar to apparatus 1000 shown in FIG. 1A except that phosphor layer 20 of transducer 22 is directly coated over digital light sensor 10. Visible or NIR light emitted by phosphor layer 20 is directly incident and spatially resolved by digital light sensor 10 without need of an image forming optic. Illumination source 30 is shown to illuminate the front side of phosphor layer 20.
[0076] FIG. 5 shows a schematic of a digital infrared detection apparatus 1100 according to another embodiment of the present disclosure. Scene E provides both infrared (IR) light and non-infrared light. Digital light sensor 10 is sensitive to the non-IR light, for example, UV, visible, or NIR light. If this non-IR light were allowed to reach digital light sensor 10, it could add unwanted background artifacts, and hence contaminate, the desired infrared image. Furthermore, if the non-IR light were allowed to reach phosphor layer 20, the non-IR light could itself charge phosphor layer 20 in an undesirable manner, for example, with a non-uniform energy distribution. This unwanted effect could degrade the image quality of the infrared image. Apparatus 1100 is similar to apparatus 1090 shown in FIG. 4 with the addition of optical filter 90, discrete from phosphor layer 20. Optical filter 90 substantially transmits infrared light and substantially blocks non-infrared light. FIG. 5 shows filter 90 substantially reflecting the non-infrared light. Alternatively, filter 90 may substantially absorb, or partially absorb and partially reflect, the non-infrared light. FIG. 5 shows filter 90 positioned immediately in front of phosphor layer 20 so as to block non-IR incidence upon phosphor layer 20 and, because phosphor layer 20 may be at least partially transparent to the non-infrared light, also upon digital light sensor 10. Alternatively, filter 90 may be positioned anywhere between scene E and phosphor layer 20, including in physical contact with phosphor layer 20.
[0077] FIG. 6A shows a schematic of a digital infrared detection apparatus 1110 according to another embodiment of the present disclosure. Apparatus 1110 is similar to apparatus 1000 shown in FIG. 1A, with phosphor layer 20 of transducer 22 thermally coupled to a temperature control device 120 for controlling the temperature of phosphor layer 20. Temperature control device 120 may include a cooling mechanism, for example a thermoelectric cooler, for cooling phosphor layer 20 to reduce thermal energy. Unwanted thermal energy could otherwise cause spontaneous emission and resulting unwanted background artifacts detected by digital light sensor 10, due to trapped electrons escaping from their traps. Also, temperature control device 120 may include a heating mechanism, for example a resistive heater. A heating mechanism can temporarily heat phosphor layer 20 during periods when digital light sensor 10 is insensitive to, or gated to not detect, light. Added heat can help to accelerate afterglow or the escape of electrons from shallow traps to help reduce unwanted background artifacts that would otherwise contaminate the signal detected by digital light sensor 10 during image capture. Generally, temperature control device 120 could include both cooling and heating mechanisms for optimizing the thermal processing of phosphor layer 20 to minimize the unwanted background that would otherwise contaminate the signal detected by digital light sensor 10 during image capture.
[0078] FIG. 6B shows a schematic of a digital infrared detection apparatus 1120 according to another embodiment of the present disclosure. Apparatus 1120 is similar to apparatus 1090 shown in FIG. 4 with both phosphor layer 20 and digital light sensor 10 thermally coupled to temperature control device 130. This arrangement helps to control the temperature of both phosphor layer 20 and digital light sensor 10. Temperature control device 130 may include a cooling mechanism, for example a thermoelectric cooler, for cooling phosphor layer 20 to reduce thermal energy. Excessive thermal energy could otherwise cause spontaneous emission, and the resulting unwanted background detected by digital light sensor 10, due to trapped electrons escaping from their traps. Cooling of digital light sensor 10 can also help to reduce dark current inherent to digital light sensor 10. Also, temperature control device 130 may include a heating mechanism, for example a resistive heater. A heating mechanism can help for temporarily heating phosphor layer 20 during periods when digital light sensor 10 is insensitive to light, or gated to block light detection. This can help to accelerate afterglow or the escape of electrons from shallow traps for reducing unwanted background noise that would otherwise contaminate the signal detected by digital light sensor 10 during image capture. Heat can also help for temporarily accelerating the depletion of residual image that may accumulate in digital light sensor 10. Generally, temperature control device 130 could include both cooling and heating mechanisms for optimizing the thermal processing of phosphor layer 20. This arrangement can help to reduce unwanted background noise that would otherwise contaminate the signal detected by digital light sensor 10 during image capture, as well as to improve the performance of digital light sensor 10 itself.
[0079] FIG. 7 shows a schematic of a digital infrared detection apparatus 1130 according to another embodiment of the present disclosure. Apparatus 1130 is similar to apparatus 1000 shown in FIG. 1A and is shown in a housing 32, with transducer 22 and its phosphor layer 20 outside the housing 32 as an external component of the apparatus. As such, infrared light may be incident upon phosphor layer 20 from any direction in order to form an infrared pattern J.
[0080] FIG. 8 shows a timing synchronization diagram coordinated and controlled by control logic processor 60 (FIGS. 1A-7) for still image capture according to a method of the present disclosure. A “Start trigger” signal from control logic processor 60 to digital light sensor 10 triggers the start of an image frame capture. An “Optical Charging Light” signal defines the timing of a momentary charging period for energizing repetitively pulsed illumination source 30 for recharging phosphor layer 20. Once charging is suspended, a “Photocharge acquisition” signal defines each photocharge acquisition period during which digital light sensor 10 acquires accumulated photocharge from the visible or NIR pattern provided by phosphor layer 20 of transducer 22. As the relative timing synchronization shows, optical charging and photocharge acquisition cannot happen at the same time. A gating mechanism, as described previously, is used to control this synchronization between transducer charging and reading the digital light sensor “photocharge” signal resulting from external field excitation of the transducer by light from the object scene. Digital light sensor 10 is repetitively gated with alternating timing with respect to repetitively pulsed illumination source 30, so that digital light sensor 10 accumulates image data from the object scene only during intervals when it is not being charged. The number of time periods allowed for a complete image acquisition can be programmable or triggered by a stop trigger signal. An “Accumulated photocharge readout as image frame” signal shows readout timing for the accumulated photocharge and delivery to control logic processor 60 at completion of image capture.
[0081] Synchronization is similarly implemented for video capture. FIG. 9 shows a timing diagram according to a method of the present disclosure for video capture. Control logic processor 60 generates a “Start trigger for video frame” signal to trigger the start of capture of each video frame from digital light sensor 10. An “Optical Charging Light” signal defines the timing of a momentary charging period for energizing repetitively pulsed illumination source 30 for recharging phosphor layer 20. After suspending the charging period, a “Photocharge acquisition” signal then defines each photocharge acquisition period during which digital light sensor 10 acquires photocharge corresponding to the visible or NIR light pattern provided from phosphor layer 20. As was described for the timing synchronization diagram of FIG. 8, optical charging of the transducer and photocharge acquisition from the transducer cannot happen at the same time. A gating mechanism is used to control synchronization between charging the transducer and obtaining the transducer signal resulting from external field excitation. Digital light sensor 10 is repetitively gated with alternating timing with respect to repetitively pulsed illumination source 30, so that digital light sensor 10 accumulates image data from the object scene only during intervals when it is not being charged. The number of time periods allowed for a complete image capture may be programmable or triggered by a stop trigger signal. A “Photocharge from each exposure readout to video frame” signal shows readout timing for each exposure and delivery to control logic processor 60 for each video frame.
[0082] It is therefore clear that an object of this disclosure is to advance the art of infrared imaging by providing an apparatus for digital infrared imaging, comprising a gateable digital light sensor, an optically-chargeable transducer with a phosphor layer for transducing an infrared light pattern incident upon the phosphor layer into a visible or NIR light pattern that is imageable by the digital light sensor, and a repetitively pulsed light source for repetitively recharging the phosphor layer, wherein the digital light sensor is repetitively gated opposite to the repetitively pulsed light source during image or video capture.
[0083] The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the scope of the invention as described above, and as noted in the appended claims, by a person of ordinary skill in the art without departing from the scope of the invention.
