 |
Claims  |
|
|
I claim:
1. A method of illuminating a treated or untreated deposition of material
for forensic examination, comprising the steps of:
(a) generating light having a wide range of wavelengths;
(b) directing said light toward a reflective diffraction grating;
(c) repeatedly scanning through a range of output light bandpass
wavelengths by adjusting the relative position between an exit slit and
said grating to result in passage through said exit slit of different
desired bands of wavelengths of output light from portions of said light
reflected by said grating; and
(d) directing the scanned wavelength output light through a filter, having
a pass characteristic which substantially passes the desired bands and
blocks light having a wavelength in an expected range of fluorescence of
the deposition, toward said deposition to be examined.
2. A method as in claim 1, wherein said direction of output light is
achieved through the use of a flexible optic waveguide with an input end
coupled to said exit slit and an output end which is oriented to
illuminate said deposition.
3. A method as in claim 2, wherein said filter is attached to said output
end.
4. A method as in claim 3, wherein said flexible optic waveguide comprises
a liquid optic member.
5. A method as in claim 4, wherein said adjustment of the relative
positions of said exit slit with respect to said grating is achieved by
rotation of said grating.
6. A method as in claim 1, wherein said adjustment of the relative
positions of said exit slit with respect to said grating is achieved by
rotation of said grating.
7. A method as in claim 1 wherein said movement is controlled by an
electronic control and a hand held remote control pad.
8. A method as in claim 1 further comprising the step of detecting
fluorescence of said deposition through an emission filter.
9. A method as in claim 8 wherein a long pass filter is used as said
emission filter.
10. Apparatus for illuminating a deposition of material and causing it to
fluoresce for forensic examination, comprising:
(a) a light source emitting light having a range of wavelengths;
(b) a reflective diffraction grating formed in high temperature epoxy and
positioned to receive light from said light source;
(c) a first optical coupler, coupled to said light source, positioned and
configured to couple said light to said reflective diffraction grating;
(d) an exit slit;
(e) support structure supporting said optical coupler, grating and exit
slit to continuously scan through a plurality of selectable relative
positions to pass through said slit a desired band of wavelengths of
output light from portions of said light reflected by said grating; and
(f) a filter positioned to receive said output light and allow a portion
thereof to pass through said filter, said filter having a band
characteristic substantially passing said desired band and rejecting light
at wavelengths of expected fluorescence of the deposition.
11. Apparatus in claim 10, further comprising:
(g) a bendable second optical coupler coupled to said exit slit and
directing said output light through an output end toward said deposition
to be examined.
12. Apparatus as in claim 11, wherein said bendable second optical coupler
comprises a fiber optic member.
13. Apparatus as in claim 12, wherein said optic member comprises a liquid
optic member.
14. Apparatus as in claim 10, wherein said support structure comprises a
rotatable support for rotatably supporting said grating.
15. Apparatus as in claim 10, further comprising an electronic control and
a hand held remote control pad coupled to said support structure and
controlling said support structure.
16. Apparatus as in claim 15, wherein said pad has a number of preset
wavelength selections.
17. Apparatus as in claim 8, wherein said exit slit may be varied in width
to select a number of different bandpass widths.
18. Apparatus as in claim 11, wherein said bendable second optical coupler
is a flexible light guide and said filter is a short pass filter with a
cut off wavelength of 500 nm or 550 nm with at least 10.sup.-8 blocking in
the fluorescence range, said filter being mounted at the end of said
flexible light guide.
19. Apparatus as in claim 11, wherein said filter located at said output is
a short pass filter.
20. Apparatus as in claim 11, wherein said filter is located at said output
end and comprises a pair of band pass filter members arrayed in cascade.
21. Apparatus as in claim 20, wherein said band pass filter members have
substantially the same center wavelength and different bandwidths.
22. Apparatus as in claim 10, further comprising a filter for filtering
light from said light source before it falls on said grating.
23. Apparatus as in claim 10, further comprising a viewing filter for
receiving light from said deposition, said viewing filter having a pass
characteristic which results in passage of light at an expected emission
wavelength.
24. Apparatus as in claim 10 wherein fluorescence of said deposition is
detected through an emission filter.
25. Apparatus as in claim 24 wherein said emission filter is a long pass
filter.
26. A method of illuminating a deposition of material whose location is
unknown for forensic examination, comprising the steps of:
(a) generating light having a wide range of wavelengths;
(b) directing said light toward a wavelength selecting member;
(c) repeatedly scanning said wavelength selecting member through a range of
output light wavelengths by adjusting the relative position between an
exit port and said wavelength selecting member to result in passage
through said exit port of different desired bands of wavelengths of output
light from portions of said light output by said wavelength selecting
member; and
(d) directing the scanned wavelength output light through a filter, having
a pass characteristic which substantially passes the desired bands and
blocks light having a wavelength in an expected range of fluorescence of
said deposition and directing the scanned filtered wavelength output light
toward a plurality of sites in order to detect and illuminate said
deposition to be examined.
27. A method as in claim 26 further comprising the step of detecting
fluorescence of said deposition through an emission filter.
28. A method as in claim 27 wherein a long pass filter is used as said
emission filter.
29. Apparatus for illuminating a deposition of material and causing it to
fluoresce for forensic examination, comprising:
(a) a light source emitting light having a range of wavelengths;
(b) a wavelength selecting member formed in high temperature epoxy and
positioned to receive light from said light source;
(c) a first optical coupler, coupled to said light source, positioned and
configured to couple said light to said wavelength selecting member;
(d) an exit port;
(e) support structure supporting said optical coupler, wavelength selecting
member, and exit port to continuously scan through a plurality of
selectable relative positions to pass through said port a desired band of
wavelengths of output light form portions of said light output by said
wavelength selecting member; and
(f) a filter positioned to receive said light from said light source and
allow a portion thereof to pass through said filter and fall on said
wavelength selecting member, said filter having a pass characteristic
substantially passing said desired band and rejecting light at other
wavelengths to minimize the generation and transmission of noise in the
apparatus.
30. Apparatus as in claim 29 wherein fluorescence of said deposition is
detected through an emission filter.
31. Apparatus as in claim 30 wherein said emission filter is a long pass
filter.
32. Apparatus for illuminating a deposition of material and causing it to
fluoresce for forensic examination, comprising:
(a) a light source emitting light having a range of wavelengths;
(b) a wavelength selecting element formed in light temperature epoxy and
positioned to received light from said light source;
(c) a first optical coupler, coupled to said light source, positioned and
configured to couple said light to said wavelength selecting member;
(d) an exit port;
(e) support structure movably supporting said optical coupler, wavelength
selecting member and exit port to select one of a plurality of selectable
relative positions to pass through said port a desired band of wavelengths
of output light from portions of said light output by said wavelength
selecting member; and
(f) a filter positioned to receive said output light and allow a portion
thereof to pass through said filter, said filter having a pass
characteristic substantially passing said desired band and rejecting light
at wavelengths of expected fluorescence of the deposition.
33. Apparatus as in claim 32, wherein fluorescence of said deposition is
detected through an emission filter.
34. Apparatus as in claim 33 wherein said emission filter is a long pass
filter.
35. Apparatus as in claim 34, wherein said emission filter comprises a pair
of goggles. |
|
 |
|
 |
Claims |
|
|
|
Description |
|
|
TECHNICAL FIELD
The present invention relates to a method for the examination of surfaces
for fingerprints, blood, hair or other forensic materials for the purpose
of developing evidence relating to the past history of the surface.
BACKGROUND
Starting at the end of the nineteenth century, crime fighters began to use
and develop what has grown into a substantial body of technological tools
designed to detect and/or enhance physical evidence. One of the earliest
techniques of this kind to receive widespread application is the dusting
of fingerprints. Light sources were also among the first tools used in
this field. Hence the classic icon of the gumshoe, flashlight in hand,
searching for evidence at the dimly lit crime scene.
When a fingerprint is fresh, the oil which forms the print generally
follows the pattern of the fingerprint ridges in the finger which made the
print. If a fine dust is applied to the surface of a fresh print, the dust
tends to adhere to the oils in the fingerprint, thus forming a pattern
which generally reveals the pattern of the fingerprint.
Fingerprint dusts were initially selected for their color contrasting
qualities as compared to the background. Thus white dust was used to
enhance a fingerprint on a black object and vice versa. Even where the
oils of a fingerprint have lost their tackiness due to aging or other
phenomena, the amino acids into which they break down do cause a minute
etching of many surfaces. While this etching is often not visible to the
naked eye, and may not become visible with the application of a colored
powder, extremely fine fluorescent dusting powders will reveal the
fingerprint pattern when illuminated under high intensity light. Today,
many materials, such as dyes, in addition to fluorescent dusting powders
are used. Inspection of the evidence is done with specialized light
sources. These light sources usually comprise a high intensity source and
a filter which passes light having a limited range of wavelengths.
Depending upon the material used, which material may be either a
fluorescent dusting powder, dye, or other marker material, light having a
wavelength which substantially coincides with a known excitation
wavelength of the marker is employed. The characteristic of the marker is
that, upon illumination with light at one of its excitation wavelengths,
it will fluoresce, or emit light. Such fluorescence is typically at a
longer wavelength as compared to the excitation wavelength.
Examination of evidence is also enhanced through the use of color filtering
glasses or barrier filters, whose color filtering characteristics are
tuned to maximize the image to be detected. As noted above, the excitation
wavelength is varied through the use of filters at the source. While such
devices are very efficient in filtering light, every filter has its own
fixed characteristics. These include its center wavelength, bandwidth and
transmission coefficient. Thus, if one wishes to have flexibility, it is
necessary to have a wide range of filters having different center
wavelengths and different bandwidths. This is both cumbersome and
expensive. Moreover, as new dyes and powders are introduced, old filters
can become obsolete or unnecessary.
In an attempt to provide convenience and flexibility, some light sources
used for forensic examination come with a mechanical filter assembly,
which allows the introduction of one of about a half dozen filters into
the path of the light source to provide the desired wavelength
illumination. While this does solve the problem of providing a convenient
and easy way to use a light source, obsolescence and limited wavelength
and bandwidth selection remain.
In an attempt to overcome some of these disadvantages, earlier forensic
illumination systems have attempted to achieve a measure of tunability by
mounting an interference filter for angular rotation. Generally, such
angular rotation results in a change in angle of incidence with respect to
the filter input and a relatively small variation in the encountered path
length between the functional layers in the interference filter for light
passing through the filter in a fixed direction. In accordance with
Bragg's Law, this results in different wavelengths being passed by the
filter.
In the above-referenced disclosure of Purcell, a system is disclosed which
provided a high intensity light source which is continuously adjustable to
vary the center frequency of a band of wavelengths. At the same time, the
flexibility of varying the bandwidth of this band was also possible. The
same was done with a single light source and a single filtering apparatus.
At the same time that was achieved with a mechanical configuration that is
both reliable and rugged. Finally, that system was easily portable, and
capable of outputting light sufficient for close up analysis of surfaces
bearing such material as oils, semen, blood and so forth.
In that system, a method and apparatus for illuminating a deposition of
organic material such as, blood, sweat or oil for forensic examination was
also provided. A light source emitted light having a range of wavelengths.
A first optical coupler or light pipe was positioned and configured to
reflect the light toward a reflective diffraction grating. A supportable
structure supported, at a selectable relative position, an exit slit and
the grating to pass a desired band of wavelengths of output light from
portions of the light reflected by the grating. A bendable second optical
coupler was coupled to the exit slit and directed the output light toward
the deposition to be examined. The bendable second optical coupler
comprised a liquid fiber optic member. The support structure rotated the
grating. An electronic control and a hand held remote control pad was
coupled to the support structure and controlled the support structure.
As can be seen from the above, numerous advantages are provided in such a
continuously adjustable diffraction grating based system. Naturally, it is
desirable to have the possibility of the highest possible intensity output
light at the selected wavelength. However, such a brute force approach
results in increased power consumption and excessive heat energy,
stressing the rest of the system. In an attempt to achieve better results
without aggravating this problem, the above disclosure of Purcell utilizes
an IR blocking filter to filter the light source thus allowing only
filtered and relatively low intensity light to fall on the grating. This,
however, also has an adverse impact on the amount of energy output by the
forensic light source, particularly in the UV range. In addition, the use
of the filters, because they are exposed to a high intensity source,
results in there being another element subject to deterioration and
replacement.
SUMMARY OF THE INVENTION
The invention, as claimed, is intended to provide a remedy. It solves the
problem of how to provide an improved forensic light source by having a
continuously adjustable output wavelength. The light output is capable of
generating an image having an improved signal-to-noise ratio. At the same
time, this is achieved with long component life while providing the
flexibility of also being able to select a conventional filter-based
output.
In accordance with the preferred embodiment, this is achieved by using a
low noise light source for illuminating a treated or untreated deposition
of material for forensic examination. A light having a wide range of
wavelengths is generated. The light is directed toward a reflective
diffraction grating. The relative position between an exit slit and the
grating is repeatedly adjusted resulting in passage of different desired
bands of wavelengths of output light from portions of the light reflected
by the grating through the exit slit. The output light is directed through
a filter, toward the deposition to be examined. The filter has a pass
characteristic which substantially passes the desired bands and blocks the
light that has a wavelength in an expected range of fluorescence of the
deposition.
BRIEF DESCRIPTION OF THE DRAWINGS
One way of carrying out the invention is described in detail below with
reference to drawings which illustrate only one specific embodiment of the
invention and in which:
FIG. 1 is a front plan view of a forensic illumination system constructed
in accordance with the present invention;
FIG. 2 is a side view of the system illustrated in FIG. 1;
FIG. 3 is top plan view of layout of the components of the system
illustrated in FIGS. 1 and 2;
FIG. 4 is rear plan view of a preferred monochromator section of the
embodiment of FIGS. 1-3;
FIG. 5 is a view along lines 5--5 of the monochromator section of FIG. 4;
FIG. 6 is a top plan view of a mirror assembly for providing visible and
infrared light outputs for the inventive system;
FIG. 7 is a view of the mirror assembly along lines 7--7 of FIG. 6;
FIG. 8 is a view in cross-section of the output light port of the inventive
system;
FIG. 9 is a view along lines 9--9 of FIG. 8.
FIG. 10 is a view of the output port and filter holder of the light output
cable of the inventive system;
FIG. 11 is a graph illustrating output energies and band pass
characteristics for using the inventive system;
FIG. 12 is a graph illustrating fluorescent energies and detector band pass
characteristics; and
FIG. 13 is a perspective view of filter goggles used in the method and
apparatus of the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
A forensic lighting system 10 constructed in accordance with the present
invention is illustrated in FIGS. 1-3. System 10 comprises a housing 12
and a carrying handle 14. Ventilation is provided by a pair of ventilation
fan openings 16 and 18.
Light output from system 10 is provided via a flexible hose-like
monochromator light output cable mounting assembly 20 (FIG. 1), which is
adopted to mate with the end of a liquid optic coupling cable 22 as
illustrated in FIG. 4. Cable 22 is typically two meters long and has a
diameter of eight millimeters, and is of known construction. Manipulation
of bandwidth and center wavelength is achieved through a remote control
box which is coupled to system 10 by a cable such as that described in the
above application of Purcell. As can be seen in FIGS. 1-3, the housing,
which takes the shape of a rectangular box and is easily portable, is
completed by a plurality of rubber feet 24, which serve to support the
inventive system 10 while it is in use resting on a floor, table or the
like.
With reference to FIG. 3, system 10 generally comprises a light source 26
which comprises an inner light source housing 28, which houses a lamp and
reflector. The housing of light source 26 is provided with a ventilation
opening 30. The chamber 32 defined by housing 28 of light source 26
communicates with the ambient through ventilation openings 34 to which it
is coupled by a pipe 38, shown in cross section. Ambient air is admitted
to conduit 38 by ventilation openings 34 causing a flow in the directions
indicated by arrows 40 and 42. This air flow is powered by a fan 44.
Because this air flow is limited to an isolated space consisting of the
insides of pipe 38, chamber 32, and fan 44, any environmental dust or the
like entrained by fan 44 is isolated from the rest of the system.
Light source 26 is designed around a conventional 300 Watt xenon short arc
lamp. Source 26 is of the type manufactured as a complete subassembly by I
L C Technology of Sunnyvale, Calif. under catalog number R300-3. A similar
unit is available from O R C Corporation of Freehold, N.J. The light from
lamp 50 is focused and concentrated by the combination of a built-in
reflector and other standard optics, including a lens 46.
Wavelength selection is provided by a monochromator grating assembly 48,
shown in greater detail in FIG. 4. Referring to FIG. 4, monochromator
assembly 48 comprises a concave focussing holographic grating 50. Grating
50 has a groove density of 1200 grooves per millimeter and is blazed at
450 nanometers. This grating is replicated in a high temperature epoxy
which is deposited on a Pyrex concave substrate. Grating 50 has a radius
of curvature of about 112.1 millimeters and a side square dimension of 32
millimeters. This grating is available from Instruments SA, Inc. of
Edison, N.J.--USA under part number 524-00.120. Naturally, other gratings
may be used, provided that they cover the desired wavelength for the
system. To the extent economical, larger gratings are preferred, because
they are able to collect more output light.
Grating 50 is positioned within monochromator assembly 48 and oriented to
be co-planar with a plane perpendicular to the front face 52 of housing
12. Generally, in order to accommodate different wavelengths, the plane of
the grating is maintained perpendicular to front face 52 while being
rotated in the directions indicated by arrow 54. Referring to FIGS. 4 and
5, light 56 is input into the system along path 58 in the direction
indicated in FIG. 4. Light enters the system through an inlet slit 60,
having a height 62 equal to 13 millimeters, and a width 64 of 9
millimeters.
Depending upon the position of grating 50, reflected output light 56 has a
wavelength ranging about any desired value within the parameters of
grating 50. In the illustrated example, this means a range from a low of
300 nm to a high of 800 nm. Output light 66 passes through outlet slit 68.
The dimensions of outlet slit 68 are substantially the same as inlet slit
60. Output light 66 is then passed through a lens 70 which has a diameter
of about 1.88 centimeters and a focal length of about 28 millimeters. This
results in focussing light toward cable mounting assembly 20 which is
mounted on the outside surface 72 of the top plate 74 of housing 12.
Wavelength variation can be achieved through two alternative mechanisms
provided in accordance with the present invention. More particularly,
referring to FIGS. 4 and 5, automatic wavelength variation is achieved
using a stepper motor 76, whose output shaft 78 is coupled to a pulley 80.
As the motor is activated, pulley 80 is rotated, resulting in transferring
power to a second pulley 82 by means of a coupling belt 84. Pulley 82
drives a rotatable mount upon which grating 50 is mounted, using a
mechanism such as that illustrated in U.S. Pat. No. 5,192,981, of Slutter
issued Mar. 9, 1993.
As an alternative to the rotation of the grating through the use of stepper
motor 76, the grating may be manually rotated by rotation of a knob 86
which is coupled to a shaft 88 and one of the gears 90 of the gear train
illustrated in FIGS. 4 and 5. Shaft 88 is mounted within a ball bearing
mounting 89.
In the case of automatic wavelength selection, absolute wavelength
selection can be achieved by an initial sequence in which stepper motor 76
moves the grating to a known position and then counts from that known
position the required number of steps to achieve a desired wavelength.
Alternatively, the wavelength indicated by the calibrated counter coupled
to knob 86 may be entered into the microprocessor motor control through
the remote control key pad. Thereafter, wavelength selection may be made
by moving a known number of step displacements from the last known
wavelength position. Insofar as the coupling mechanism between pulley 82
and the support for grating 50 linearly varies the output wavelength of
light 66 in accordance with the number of steps with which the stepper
motor is activated, such relative wavelength calculations are
straightforward and the control mechanism is thus simple and reliable.
In the case of manual selection of wavelength, a switch 92 is used to
disconnect power from the automatic drive circuitry for motor 76, thus
allowing knob 86 to be rotated to vary wavelength. While the selection of
wavelength can be controlled well in this mode, the relative variation of
wavelength may be the primary concern, insofar as use in this mode
contemplates illumination of a desired deposition with the light output of
the monochromator followed by rotation of the knob until a desired image
appears, after which the contrast is visually maximized by rotation of
knob 86. Typically, photography would then be performed under the
wavelength visually determined to result in maximum contrast. In this
respect, it is contemplated that a person may use colored goggles (FIG.
13) or look through a camera filter whose color response is substantially
matched to that of a filter through which the camera will take a picture
of the desired deposition.
The monochromator assembly is cooled by the provision of an exhaust fan 94
(FIG. 3) which exhausts air in the direction indicated by arrow 96. Input
air is provided to the system in the direction indicated by arrow 98
through a venting grid 100. The provision of separate isolated air flows
for lamp cooling and cooling of the monochromator and other components
inside housing 12 results in minimizing the flow of possible entrained
particles through the exposed optical components. It is noted that while
grating 50, for example, is not directly exposed to the flow of air, a gap
102 between a top plate 104 and the main part of the monochromator
subhousing 106 ensures the escape of hot air as is illustrated most
clearly in FIG. 5. If desired, one or more sides of the monochromator
housing 106 may be removed or made perforated to improve the cooling
effect of air input through the vent 100. In addition, vent 100 may be
provided with a filter in order to minimize the input of entrained
particles from the air.
As can be seen from the above, means are provided for directly outputting
light from light source 26 onto grating 50, for selection of a narrow band
of colored light useful for exciting particular materials and allowing for
inspection and photography. For some purposes, however, simple infrared or
visible light may be desired. Referring to FIGS. 3, 6 and 7, the same can
be achieved by introducing a mirror assembly 110 into the space between
the lens 46 and inlet slit 60 of the monochromator. This is in contrast to
the function of the instrument when in the position illustrated in FIG. 3
where mirror assembly 110 is positioned out of the path between lens 46
and inlet slit 60 of grating assembly 48.
Referring to FIGS. 6 and 7, mirror assembly 110 comprises a support bracket
112 to which a monorail cylindrical bar 114 is secured by a pair of bolts
116. Also secured to support bracket 112 is a key comprising a cylindrical
bar 118 which is held in position by a pair of bolts 120. Support bracket
112 is secured to the bottom plate 122 of housing 12 by a pair of bolts
124.
A mirror support plate 126 is mounted on a monorail follower pipe 128 which
is slidably mounted on bar 114. A key engagement follower 130 having a
hole 132 is rigidly secured to pipe 128 in order to provide for a
rotational stability of pipe 128 and the mirror support plate 126 secured
thereto by bolts 134.
As can be seen with particular reference to FIGS. 3 and 6, an infrared
reflecting mirror 136 is mounted on plate 126 by a mirror mounting bracket
138 which is secured to plate 126 by bolts 140. Infrared reflecting mirror
136 reflects infrared light incident on it as indicated by light 56 in the
direction indicated by arrow 142.
While infrared light is reflected by mirror 136 in the direction indicated
by arrow 142, visible light continues through mirror 136 and is caused to
fall in the same direction upon mirror 144. Mirror 144 is a simple
silvered surface which reflects all wavelengths of visible light incident
on it, causing the light to proceed in the direction indicated by arrow
146. As can be seen in FIG. 6, mirror 144 is mounted on a bracket 148
which is secured by bolts 150 to plate 126.
As can be seen particularly with reference to FIG. 7, pipe 128 is secured
to an operator arm 152 which has a manual gripping knob 154 and a stop 156
mounted on it.
In the position illustrated in FIGS. 6 and 7, infrared and visible light
are provided along the paths indicated by arrows 142 and 146. This causes
light to fall upon infrared output port 152 which receives infrared light
reflected by mirror 136. At the same time, visible light is reflected
along the path indicated by arrow 146 to visible light output port 154
also located on the front face 52 of housing 12.
If one is not desirous of obtaining infrared or visible light and wishes,
instead to obtain the output of the monochromator at a particular narrow
band of wavelengths, knob 154 is pulled forward bringing the mirror
assembly from the position illustrated in FIGS. 6 and 7 to the position
illustrated in FIG. 3. Movement of the mirror assembly in the directions
indicated by arrow 156 is achieved because pipe 128 is slidably mounted
for such movement on bar 114. Movement is limited by stop 156 which, in
the furthest forward position, butts against front face 52 of housing 12,
as illustrated in FIG. 3. At the same time, follower 130 slides along bar
or key 118 which passes through hole 132. The rearward position of the
mirror assembly illustrated in FIG. 6 is maintained by a plunger ball
assembly 158 which mates with an annular detente groove 160 in bar 114. A
groove may also be provided for the frontmost position of the mirror
assembly.
The construction of ports 152 and 154 is illustrated in FIGS. 8, 9 and 10.
Light 162 falling on the fiber mount assembly port 152 is focussed by a
lens 164 for coupling to a fiber optic member 166 illustrated by phantom
lines in FIG. 8. Fiber optic member 166 includes a fiber optic receiving
port 168 which mounts in locator assembly 170. A positive engagement
between fiber optic member 166 and locator assembly 170 is provided by a
ball and plunger assembly 172 which engages an annular groove 174 on a
locking rod 176 which is a part of the conventional fiber optic light
guide used. The locator assembly 170 is secured to the front face 52 of
housing 12 by a pair of bolts 178. Fiber optic member 166 includes an
elongated fiber optic coupling cable 180.
As illustrated in FIG. 10, at the other end of fiber optic cable 180 is an
output coupling filter holder assembly 182 which includes a ball and
plunger assembly 184 for maintaining the fiber optic cable 180 in
position. The ball and plunger assembly provides for the mounting of
filters. The coupling filter holder assembly 182 includes a substantially
cylindrical housing 188 which is formed with a bore 190 which may receive
one or two filters 192 which may be held in position by set screws 194 or
any other suitable means. Filters may be changed by simply removing one
assembly 182 and replacing it with another having a filter of desired
characteristics, such as those detailed below. In addition, two such
filters may be used at the same time to obtain sharper skirt
characteristics, sharper cut-off and higher blocking in the band reject
region on the order of 10.sup.-9.
In use, the inventive system functions as a versatile and effective light
source. It has all of the advantages of prior art filter based systems and
a monochromator based output of superior quality. In particular, with the
mirror assembly 110 located in the position illustrated in FIG. 3, the
light output of the 300 watt xenon source 26 falls directly on grating 50
causing the selective release through outlet slit 68 of a narrow band of
wavelengths. The upper and lower limits of the light output from the
system and thus the color of the output light may be varied by rotation of
knob 86. Knob 86 is also coupled to a counter 200, which is of the type
well known and widely available on the market and sold by such companies
as Veeder Root. Counter 200 is coupled to knob 86 which in turn is coupled
by a series of gears to a rotatably mounted grating support 202 through
the sine wave characteristic coupling mechanism described in U.S. Pat. No.
5,192,981 of Slutter.
Linear rotation of knob 86, coupled by such a coupling mechanism results in
a linear variation in wavelength output by the system. Such linear
wavelength variation is extremely precise and thus allows the counter to
directly read the wavelength in nanometers, for example, with the gear
reduction ratio selected for a one-to-one correlation in a 0-999
mechanical counter, for example. Thus, once the position of the grating is
adjusted to correspond to the number on the counter, the counter is an
extremely accurate and reliable indicator of output wavelength for the
monochromator.
Likewise, the gear train between stepper motor 76 and the grating support
may be adjusted for a gearing ratio which corresponds to a one-to-one
correspondence between output wavelength in nanometers and a single step
of the stepper motor.
Insofar as all mechanical gear train systems include a certain amount of
backlash, accurate wavelength indications in both the automatic stepper
motor mode or in the manual mode may be achieved by always stopping at the
desired wavelength when the system is moving in one direction or the
other, for example, when the system is moving in the direction of
increasing wavelength. If one is increasing wavelength, it is thus is
merely necessary that the system be adjusted until the desired wavelength
is reached. However, if one is decreasing wavelength, the procedure
followed in both the automatic and manual modes is to reduce wavelength to
a value slightly below, for example 5 nanometers below, the desired
wavelength and then reverse the direction of dial movement or motor
movement and approach the desired wavelength from a smaller wavelength.
As noted above, fingerprint detection and related detection of smears of
organic or inorganic materials may be done using a wide of variety of
techniques ranging from direct detection of the substance under intense
light of a particular color, white light, or the like. Where the
characteristics of the system are known, the user may select the desired
wavelength from the monochromator using the automatic motorized mode or he
may do the same using knob 86.
As an alternative, the system may be controlled using a conventional
electronic microprocessor based system to scan through a desired range of
wavelengths and stop at desired increments of wavelength for any desired
period of time. Such operation may be automatically or manually repeated.
Such automatic repeats of a scan may be used when one wishes to repeatedly
check different areas for deposits. Such wavelength scans are of
particular value where an area has the possibility of numerous emissions
of unknown characteristics. A crime scene may be the subject of
undisturbed detection with one simply looking for materials which may
fluoresce when excited with light of an unknown wavelength. For example,
the perpetrator of a crime may have visited a site where a particular
material was located and such material may be contained on the soles of
his shoes or on his hands and remnants of that material may be left
behind. These remnants can often be detected by generally scanning a wide
range of wavelengths in a wide range of places at the crime scene.
Because of the automatic nature of repeated scans at a wide range of
wavelengths, which scans can be repeated quickly and efficiently, a wide
range of new search operations become possible and practical using the
inventive system.
With the monochromator assembly of the present invention, it is
contemplated that wavelength scans and outputs will be limited to the
ultraviolet and visible ranges. Thus, a liquid light waveguide member is
appropriate. It is also possible that if one wishes to perform searching
in the infrared range, to use a fiber optic light guide, or no waveguide
at all.
Detection of weak emissions may be compounded by the pr | | |
