The invention relates to a lens system and in particular to a telecentric zoom lens system at finite conjugate distances for use with a scintillator light source.
Optic systems are known in the art to convey optic signals from a source to a camera or other recording or viewing screen. The source of the optic signals can be any source, but one example field of use is for experiments or generated phenomena that are generated by a signal source. One example of a signal source is a chamber or other containment vessel in which an event may occur. The event may be a high-energy pulsed radiographic x-ray source. In this source, a rod-pinch x-ray diode, or other source, produces a point source having a diameter, such as for example, 1 mm diameter. The x-rays are directed at a target object. In such a source, the target object is placed at a distance, such as 1.5 meter, from the x-ray source, and a large scintillator is placed at a further distance, such as at 2.4 meters. The scintillator type may be a LYSO scintillator LYSO (Lu1.8Y0.2SiO5(Ce)) or any other type material or configuration.
It is contemplated that different-sized or type objects may be imploded within the containment vessel and the event recorded. To record the events, a lens system directs optic signals from the event to a camera or other recording or observation device. Prior art lenses and capture devices suffer from several drawbacks. One such drawback was that the existing lenses do not meet a telecentric requirement. The telecentric condition occurs when light rays emitted from any of the field points of the emitter are all parallel to each other. Prior art lenses collect light rays at various angles from different field points of an emitter. Prior art lenses collect good images from a surface emitter but do not work well with a volume emitter. Another drawback is that normal lenses have no zoom capability. Thus, when different scintillators and/or cameras are used with normal lenses, optimal resolution is not collected from the scintillator. This is a significant drawback and results in the camera being either under filled or over filled.
Another drawback to prior art lens system was that the resolution was less than desired and light collection and transmission left the resulting image light starved. Prior art lenses also resulted in undesirable signal to noise statistics of the recorded image. The innovation described below overcomes these drawbacks in the prior art.
To overcome the drawbacks of the prior art, a system is disclosed for recording an event comprising a scintillator located to receive energy from the event. A lens group that includes two or more lenses, receives the light from the scintillator and directs the light to a camera. The camera is configured to capture and record the light directed through the lens group from the scintillator to thereby record an image of one or more aspects of the event. The lens group includes two or more lenses and at least one lens is movable, relative to another of the two or more lenses, to enable a change in magnification of the image represented by the camera.
In one embodiment the event comprises generation of x-ray energy. In one configuration a mirror presented at an angle to direct the light from the scintillator to the lens group. The mirror may be a pellicle mirror. It is contemplated that the lens group may comprise a first lens group configured to receive the light from the pellicle such that the first lens group comprising one or more lenses, and a first doublet lens configured to receive the light from the first lens group and a second doublet lens configured to receive the light from the first lens group, such that the first doublet lens can move relative to the second doublet lens.
The system may further comprise a shutter configured to selectively establish an aperture to electively pass and block light traveling from the lens group to the camera. The shutter may comprise a mechanical shutter. The scintillator may comprises a LYSO scintillator or a Csl(Tl) scintillator. Csl is sesium iodide (thallium doped). In addition, the lens group may be telecentric.
Also disclosed is a method for recording an event comprising the steps of receiving energy from an event at a scintillator, the scintillator converting the energy to a light at a visible wavelength. Then, receiving the light along an light path axis at a first lens group such that the first lens group comprises one or more fixed lenses and then presenting the light from the first lens group to first zoom lens element and a second zoom lens element. At least one of the first zoom lens element or a second zoom lens element is movable in the direction the light path axis. The light is then received at an image plane of a camera and the light forms an image on the image plane such that the movement of the first zoom lens element or a second zoom lens element adjusts the size of the image on the image plane. The camera can then record the image at a selected magnification.
In one embodiment, the energy comprises x-ray energy and the scintillator converts the x-ray energy to a visible wavelength. The scintillator may comprise or consist of a LYSO scintillator or a Csl(Tl) scintillator. This method of operation may further comprise reflecting the light from the scintillator into the first lens group with a pellicle mirror. It is optional to actuate a shutter to selectively present the light to the camera.
Also disclosed is an imaging system for use with a pulsed radiographic x-ray source that includes a first lens group configured to receive light in the form of x-ray energy. A second lens group is also present and it has zoom capability, the second lens group having at least one lens that is moveable in relation to one or more other lenses in the second lens group. A shutter is configured to selectively pass the light to a camera which is configured to capture the light to form an image such that the image represents x-rays from the radiographic x-ray source.
In one embodiment, the light is generated by a scintillator which generates light in response to contact by x-ray radiation. The camera may comprise a 62 mm CCD camera and is movable along an axis, the axis parallel to the direction of the light from the second lens group. It is contemplated that the first lens group and the second lens group may establish a telecentric lens system.
Other systems, methods, features and advantages of the invention will be or will become apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description, be within the scope of the invention, and be protected by the accompanying claims.
The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. In the figures, like reference numerals designate corresponding parts throughout the different views.
A large pellicle 124 deflects the scintillator light out of the x-ray path into a zoom lens array 112, 116 coupled to a CCD camera 130. In one other embodiment, other mirrors may be utilized other than a pellicle 124, or the lens system 112 may align directly with the chamber. In one embodiment the camera 130 comprises a CCD type camera but in other embodiments any type camera may be used. In this embodiment, an eleven-element zoom lens system 112 is selected, but in other embodiment, other number of lenses may be used.
In this embodiment, the zoom lens 112 and camera 130 are as close as possible to the scintillator to maximize light collection, but in other embodiments the distance may vary. As a benefit of this embodiment, the lens system 112 is a telecentric lens design configured to minimize image blur from a volume source. To maximize the resolution of objects of different sizes, the scintillator 120 and zoom lens 112 are translated along the x-ray axis to change the zoom lens magnification.
Additional support structure is shown to support and secure the scintillator 120, pellicle 124, lens assembly 112, and the camera 130. Any support structure may be used as is discussed herein and as such, the support structure is not described in detail.
In this embodiment, the lenses weight 60 lb and are located in a 340 lb mechanical structure which is orientated vertically as shown in
In this configuration the zoom magnification is changed when different-sized recording cameras are used, such as for example a 50 or 62 mm square format camera. In other embodiments, other camera sizes may be adopted for use.
In this embodiment, the scintillator 120, which may be a LYSO type scintillator, measures 200×200 mm and is 5 mm thick. In other embodiments other sizes and thicknesses of scintillator 120 may be used, or another medium other than a scintillator may be placed between the event and the pellicle or lenses. The pellicle 124 should be considered an optional element. In this embodiment, the scintillator 120 produces blue light peaking at 435 nm, so lens materials tailored to this wavelength is preferred. In other embodiments, other wavelengths may be used and different corresponding lens material utilized. For example, the zoom lens can also use a Csl(Tl) scintillator that produces green light centered at 540 nm.
This configuration has the benefit of at least one new lens element and at least one lens may be configured to move. All lenses in both wavelength bands may have antireflective (AR) coating.
In this configuration, there are two sets of doublet lenses 208A, 208B, and a stop lens 212. These lens elements 208A, 212, 208B and the camera 130 are configured to move during zoom operations. One doublet (208A or 208B) may be configured with XY compensation. A set of lenses 216 resides between the doublet lens 208A and the pellicle 124. The lens group 216 may use fused silica for radiation damage control.
Also shown in
In one embodiment the rail system for moving the optical components makes use of a magnetic encoder 313 that doesn't require power to maintain its value. In other embodiments other automatic or manual rail systems may be used. In one example environment of use of the zoom lens system described herein is configured to allow for a 20° temperature difference between winter and summer operations. This may affect system design and tolerances.
In this configuration, zoom positions 1 and 2 show a square scintillator material 404A having measurements of 200 mm by 200 mm. A 10 mm thick calibration zone 412A is provided while a 220 mm diameter object field of view 416A is available to be imaged. For zoom positions 3 and 4, shown is a square scintillator material 404B having measurements of 160 mm by 160 mm. A 10 mm thick calibration zone 412B is provided while a 180 mm diameter object field of view 416B is available to be imaged. For zoom positions 5 and 6, shown is a square scintillator material 404C having measurements of 120 mm by 120 mm. A 10 mm thick calibration zone 412C is provided while a 140 mm diameter object field of view 416C is available to be imaged. For zoom positions 7 and 8, a square scintillator material 404D having measurements of 85 mm by 85 mm is shown. A 10 mm thick calibration zone 412D is provided while a 105 mm diameter object field of view 416D is available to be imaged.
Another novel aspect of this design is that it is a telecentric zoom lens. This means that the light is collected along the trajectory that the x-ray makes upon passing through the scintillator. Each x-ray generates light continuously along its track through the scintillator. A telecentric lens allows for light collection from a volume emitter without loss of resolution. A volume emitter is a scintillator that has thickness greater than the depth of focus of its light collecting lens. Normal lenses collect light at different angles from an object. With a prior art lens there will be image blur if the object light source is too thick. This occurs because prior art lenses work poorly when the scintillator thickness increases. Because pulsed x-ray imaging of dense targets may be starve for light, thicker scintillators are desirable. The zoom feature of this innovation means that different-sized scintillators and/or different-sized CCD cameras can be used, whereas this was not possible in the prior art.
As part of the design process and improvements, several considerations were made regarding how many lenses would be required to achieve the design constraints. For example, it was considered whether aspheric lenses be used to reduce the number of elements. Another design challenge was determining the number of elements required to move during the zoom operation when the magnifications were changed.
Turning now to
In this figure, movable doublets are lens elements 608 and 612. The mechanical shutter 512 does not move. The zoom lens operation occurs such that the movement of the magnifier lens group 608 changes image magnification for different scintillators, while movement of the adjuster lens group 612 compensates for aberration induced by the magnification change. In this configuration the stop size and position are also allowed to vary but in other embodiment these elements could be fixed. The camera is allowed to refocus through movement on rails or other movement or focusing means.
In one embodiment, the two moving doublets 608, 612 may have their elements cemented together to improve resolution performance. However, cementing large optical elements together may result in differing thermal expansion of these dissimilar large glasses which may undo the cement resulting in both exposed glue and uncoated surfaces causing deteriorated optical performance.
In one embodiment, an LED and divergent lens is positioned under the far corner of the pellicle mount and is pointing to the center of the scintillator 1012. The LED may be a blue LED or another color. This will be used during dry runs of the recording equipment without the Cygnus x-ray source. An array of resolution bars and step wedge features may line the outside of the field of view, as described in
In another embodiment, four LEDs are attached to the frame of lens 1010. Their light reflects off the pellicle and onto the scintillator and its calibration features. This provides a light source for dry runs of the imaging system without use of the Cygnus pulsed x-ray source.
It was determined that the LYSO scintillator has a peak emission at 440 nm while the Csl(Tl) has its peak emission at 540 nm. In order to accommodate future uses of this zoom lens, one or more optical elements may be AR (anti-reflectivity) coated for 390-700 nm wavelengths, with the peak transmission at 500 nm.
The lens system has several benefits over the prior art. When the x-rays are emitted from a point source of the Cygnus machine the light rays are nearly collimated passing through the thickness of the LYSO scintillator. Light is continuously produced along each x-ray track as it passes through the scintillator. However, the prior art lens system collects light at an angle to the x-ray axis. As the scintillator thickness increases, there is increased blurring of the collected image. To overcome this drawback in the prior art, use of telecentric zoom lens collects light along the direction of the x-ray axis. The prior art lens has a fixed working distance from the scintillator to its first optical element. Thus, there is a fixed magnification for the prior art imaging system, which does not provide the benefits of a zoom lens system. For example, prior art lens systems collected light from a 150 mm diameter scintillator and imaged it onto a 50 mm diameter CCD camera. But, if it is desired to use a higher-resolution CCD camera that has a 62 mm diameter, you will collect light into only 50 mm of the 62 mm diameter area available. Thus the prior art lens system was not using the available resolution of the camera. Through use of a zoom lens as proposed herein, the magnification can be changed, allowing many different camera sizes to be used.
Turning to
In one embodiment, correct focus adjustments for the telecentric zoom lens system were optimized. To set the focus correctly for a volume emitting scintillator, a special calibration plate could be inserted into the scintillator holder. This holder is designed to swap scintillators and calibration plates and still maintain correct tip/tilt alignments with the x-ray axis. These calibration plates contained an array of small Air Force resolution patterns which are used to measure resolution at different locations across the scintillator area. Different thicknesses of Sapphire windows were laid on top of some of these Air Force resolution patterns. The different thickness Sapphire windows simulated different planes of focus within the scintillator. Sapphire has almost the same index of refraction as the LYSO or Csl(Tl) scintillators. Using this technique, the CCD camera could be precisely focused at the middle of the scintillator volume emitter. After best focus was optimized using the calibration plate, the plate was exchanged for the proper scintillator.
To prove the benefit of the telecentric light collection lens versus prior art lenses, a dense target with a matrix of very small holes was inserted into chamber 108. Cygnus x-rays passed through this target to produce a matrix of very small light emitting spots at the volume emitting scintillator. Images of these dots recorded from the telecentric zoom lens were compared to images recorded on a prior art lens. For the prior art lens, the ellipticity of the dots increased as the position of the dot changed from the scintillator center to the scintillator edge. The telecentric lens system showed no change in ellipticity for any of the dots from the center position to the edge of the scintillator. If the scintillator were very thin, both the telecentric lens system and the prior art lens would both show uniform circular dots across the field of view. However, as the thickness of the scintillator increases, the prior art lens would show increasing ellipticity of the dot images at the edge of the scintillator.
The zoom lens proposed herein is much larger and capable than the prior art lens. The prior art lens shared the same vacuum as the CCD camera. This shared vacuum seal between these two components did not allow any focus adjustment in the prior art system. In the embodiment disclosed herein, the zoom lens is completely detached from the CCD camera, allowing for focus adjustments. In other embodiment, it could share the same vacuum, but that would prevent focusing.
While various embodiments of the invention have been described, it will be apparent to those of ordinary skill in the art that many more embodiments and implementations are possible that are within the scope of this invention. In addition, the various features, elements, and embodiments described herein may be claimed or combined in any combination or arrangement.
This application claims priority to and the benefit of U.S. Provisional Patent Application No. 61/780,669 filed on Mar. 13, 2013.
This invention was made with government support under Contract No. DE-AC52-06NA25946 and was awarded by the U.S. Department of Energy, National Nuclear Security Administration. The government has certain rights in the invention.
Number | Date | Country | |
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61780669 | Mar 2013 | US |