Note: Descriptions are shown in the official language in which they were submitted.
848S
~ield of the Invention
The present invention relates to optical instru-
ments, more particularly, to selective interference
light filters and optical instruments, in which they
are used,
The invention may be advantageously used in spect-
roscopy, lighting engineering, laser and optical instru-
ment making and also in space exploration.
Background Art
There are known interference light filters comp-
rising two or more groups of alternating layers of di-
electric material with different refractive index,
which have an optical thickness equal to a quarter wave
of luminous flux directed to said light filter (cf. SU,
A, 539,284; SU, A, 881,647).
Production of such filters generally involves un-
wanted complexities. Moreover, the necessary protective
coatings further complicate the manufacturing pro-
cess and impair optical properties of said filters,
that is, transmission of radiation.
Also, chemically pure materials may be required
in production of the afore-mentioned filtersO
In the known light filters a wavelength may be
continuously changed only within narrow limits.
~here are also known selective interference
light filters having a layer structure wherein each
layer reflects lurninous flow directed to said light
- 2
2~ 3s
filter. The layer structure is formed with a dielect-
ric layer deposited on a metal base and having a
phase hal~-width multiple of ~ and with an even number
of alternating quarter-wave layers of two dielectric
5 materials with high and low refractive index. Such a
combination of layers is topped with an absorbing
metal film whose thickness is much smaller than the
operating wavelength (cf. Optika i spec~roskopiya,
Volume ~0, 1976, Nauka publishers, ~eningrad,
Goldina N,D. and ~roitsky J~.~., pp 935 - 938~.
Such a light filter reflects not only the select-
ed wavelength but also other wavelengths beyond the
reflection band, which are treated as interference.
Moreover, said light filters have essentially the same
disadvantages as the light filters discussed pre-
viously.
Briei De~cription of the I~vention
It is an object of the present invention tocreate ~ selective interference light filter which
would make it possible to continuously adjust, within
wide limits, the operating wavelength in the event
of variations of the angle of incidence of luminous
flux.
Another object of the invention is to provide
essentially without change, as compared with the
prior art, the lightfilter spectral bandwidth, reflec-
tion factor and contrast.
2 ~ 8 S
Still another object of the invention is to de-
crease incident radiation background.
Yet another object of the invention is to increase
further the continuous adjustment range.
A further object of the invention is to orovide
a light filter capable of identifying a radiation spec-
trum of various substances.
One more object of the invention is to create a
light filter separating several spectral bands with dif-
10 ferent wavelengths at the same time.
There is provided a selective interference light
filter having a layer structure wherein each layer
reflects luminous radiation direc'ed to the light
fillter, in which, according to the invention, the
15 layers comprised in the layer structure are equidis-
tant with the refractive index varyinp~ periodically in
depth and are formed by exposing to at least one mono-
chromatic radiation at a predetermined wavelength an
element made of a light-sensitive material transpa-
20 rent to said radiation and placed in front of a mirroronly during the emission of radiation.
As distinct from the known interference light
filters formed by vacuum deposition of plane-parallel
layers of pure materials, the proposed light filter
25 allows continuous adjustment of the operating wave-
length within fairly wide limits.
The layer structure reflects different wavelengths,
-- 4
s
depending on the angle of incidence of light directed
to said structure.
The adjustment range of a wavelength reflected
from the layer structure depends on effective refrac-
tive index of said structure. More specifically, thegreater is the refractive index, the narrower is the
adjustment range. On the other hand, the greater the
number of layers forming the structure and the
greater the dif~erence between their refractive
indexes, the higher i9 the refractive index and the
narrower is the spectral band.
The irradiated element may be fabricated from
photoemulsion based on salts of silver or bichromized
gelatin or a photorecording polymeric medium or a
photopolymerizing composition of materials.
~ ormed by vacuum deposition are normally not
more than 30 to 40 layers. A further increase in the
number of layers re~ults in more defects. ~herefore,the
reflection factor will not be increased and the spect-
ral band will not be narrower. To obtain agreat ref-
lection factor and a narrow spectral band with a small
number of layers, use should be made of materials
characterized by a great difference between refractive
indexeq n1 and n2. Since n1 may not be less
than 1.3, n2 normally exceeds 2. As a result, the
effective refractive index is about 2 or greater.
A method of manufacturing the proposed light
-- 5
s
filterJ permits obtaining light filters with a greater
number of layers, more specifically, with some 100 to
200 layers, the thickness thereof (equal to half a
waveleneth) being provided automatically to a desired
accuracy, The effective refractive index of the layer
system remains close to the refractive index of the
source light-sensitive material (about 1.5 in the case
of photoemulsion based on salts of silver~. A greater
number of layers ensures, at a low modulation level
of the refractive index, a high reflection factor and
a narrow spectral band (essentially similar to that
of filters made by deposition), whereas a low effec-
tive refractive index provides for a wide wavelength
adjustment range.
It is preferable that the light filter accord-
ing to the invention should comprise a base accommo-
dating a layer structure. The light filter with a base
accommodating a layer structure has the following
advantages over the known light filter without a base:
greater strength due to the base strength, a higher
reflection factor, a narrower spectral band and
better contrast due to exclusion from interference
of a beam reflected from the air-layer structure
interface. Depending on the material of the base and
the operating wavelength range, the base may be used
to suppress interlerence pec~ks of orders higher than
the first working order of interference.
~r~ 85
The base may comprise at least one prism with
a layer structure disposed on its reflecting face
and luminous radiation directed to any free face
thereof. Also, the base may represent at least one op-
5 tical wedge with a layer structure arranged on its oneface and luminous radiation directed to the other face
thereof. In another embodiment of the invention the
base may be an element in the form of a lens.
The light filter comprising a base in the form
10 of a prism increases the operating wavelength adjust-
ment range.
An advantage of the light filter having a base
formed with an optical filter over the light filter
having a flat base is that the beam reflected from the
15 air-base interface is separated from interfering beams
linearly and, in addition, has another direction, as
in the ca~e of a base in the form of a prism. On the
other hand, the light filter cDmprising a wedge has
the 3ame advantage as the light filter having a flat
20 b~se, more specifically, smaller d~nensions and corres-
pondence of inpu~ and output faces.
The light filter comprising a base in the fo~n
of a lens acts both as an optical filter element and
a focusing ele~ent.
When an element of a light-sensitive material is
e~po~ d to two or more monochromatic radiations with
different wavelengths, the layer structure may have,
2~
respectively, two or more combinations of equidistant
layers, each of which corresponds to the natural wave-
length of said monochromatic radiation.
Such a light filter is polychromatic. It reflects
simultaneously two or more wavelengths, each of which
is readjusted after a change in the angle of incidence
of radiation affecting said light filter.
It is of advantage that combinations of equidis-
tant layers in the layer structure should be arranged
successively along luminous radiation directed to said
layer structure. It is also advantageous that said
layers should be spatially aligned.
Production of the proposed light filter is sub-
stantially simplified as compared with the prior art
light filter. Spatial alignment of combinations of
equidistant layers makes it possible to obtain to a
higher accuracy the relation between Preset wavelengths
upon reflection since different combinations of layers
are formed simultaneously.
It is also advantageous that two or more combina-
tions of equidistant layers should be formed by paral-
lel beams of monochromatic radiation, while the layer
structure contains separate sections comprising combi-
nations of equidistant layers corresponding to sepa-
rate sections of the wave front of luminous radiation
directed to said layer structure.
Spatially separated beams of different wavelengths
2~ s
are produced by such a light filter upon reflection.
It i~ further advantageous that the layer struc-
ture should comprise layers made equidistant in a
cross-section of said layer structure in a plane
5 which is, at the same time, perpendicular to any layer
and to the thickness variation direction thereof and
is formed by radiation characterized by a continuous
spectrum.
Such a light filter makes it possible to adjust
the wavelength both by changing the angle of incidence
of light directed to the light filter and by displacing
said light filter linearly in the vicinity of a slit
diaphragm. The proposed light filter is characterized
by fairly simple production techniques, which is an
apparent advantage over the known wedge light filter
made by wedge vacuum deposition of layers of material.
The layer structure may include a compression
means providing for a linear change in the thickness
of equidistant layers along said layer structure.
Therefore, in production of the light filter
provision is made for changing the refractive index
by fairly simple means.
The prism may have a rhomboidal section with
identical layer structures being disposed on its two
symmetrical side faces.
The prism may also have two pairs of syrnmetrical
side faces with a common symmetry ~lane. Each side
2~ s
face of one paix may accommodate layer structures.
Such a light filter is selective, as regards
the wavelength and the angle of incidence. It ref-
lects luminous radiation at only one wavelength in a
predetermined direction. Moreover, said light filter
may have smaller dimensions and reduced w~ht due to
omission of inoperative parts of the rhomboid.
To provide for accurate setting of a filtered
wavelength and monitoring of the angle of incidence
Of light directed to the layer structure, it is ad-
visable that the light filter according to the inven-
tion should comprise a case whose walls are provided
with two holes adapted, respectively, to pass radia-
tion to the layer structure and to release the filter-
ed radiation.
The layer structure may be installed in thecase in a manner allowing its turn and/or linear
displacement relative to the emitted radiation.
~ Vith such an arrangement, the outgoing filter-
ed radiation is not restricted to said hole in thecase, a feature being of appreciable importance in
embodiments of the light filter characterized by
spatial displacement of filtered radiation.
~urthermore, the light filter forming the sub-
ject of the present invention may comprise a case,one wall of which is formed by an input face of the
prism or optical wedge, while the opposite wall of
s
said case accommodates a diaphragm suited to pass
radiation to the layer structure, the layer structure
and the diaphragm being disposed in a manner allowing
relative turn and/or linear displacement.
Such filters permit scanning and/or directing
the beRm and/or adjusting the reflected wavelength.
The proposed light filter ensures continuous
variation of the operating wavelength and is charac-
terized by a narrow spectral band, high contrast and
high reflection factor.
Brief Description o$ the Drawings
Other object~ and features of the invention will
become apparent from the description of preferred
embodiment thereof, taken in col~junction with the ac-
companying drawings, wherein:
~ igure 1 shows a selective interference lightfilter according to the invention;
~ igure 2 showæ the same light filter comprising
a base in the form of a prism according to the inven~
tion;
~ igure 3 shows the same light filter comprising
a base in the form of an optical wedge according to
the invention;
~ 'igure 4 shows the same light filter comprising
a base in the form of a lens according to the in-
vention;
~igure 5 depicts a light filter incorporating
1 1
2 ~ 8 S
several prisms according to the invention;
~ igure 6 depicts a light filter comprising
several optical wedges according to the invention;
Figure 7 shows a light filter with combinations
of layers disposed successively in the direction of
radiation according to the invention;
~ igure 8 shows a light filter with spatially
separated combinations of layers according to the
invention;
~igure 9 shows a light filter with spatially
aligned combinations of layers according to the
invention;
~ igure 10 shows a light filter enabling conti-
nuou~ adjustment of a filtered radiation wavelength
according to the invention;
~ igure 11 depicts a light filter comprising
means for compressing a layer structure according to
the invention;
71'igure 12 shows the same light filter with comp-
ressed layers according to the invention;
~ igure 13 shows a light filter with a basehaving a rhomboida]. section according to the inven-
tion;
~ i~ure 1~ shows a light filter comprising a
base whose section represents an isosceles triangle
according to the invention;
~igure 15 sh~ws a light filter with an intrica-
_ 12
X~ 'lB5
tely shaped base according to the invention;
Figure 16 shows a light filter comprising acase according to the invention; and
Figure 17 shows another embodiment of the light
filter comprising a case according to the invention.
Detailed Description of the Invention
Referring to the drawings the selective inter-
ference light filter forming the subject of the pre-
sent invention comprises a layer structure 1 (Figure 1)
made up of equidistant layers 2, 3, ~ and 5 with re-
fractive index periodically varying in depth. Produc-
tion of such a light filter-is diagrammatically illu~qt-
rated in ~igure 1. A parallel lu~inous flux G is
directed to an element of a suitable transparent ligh~
-sensitive material through an optical system 7, said
flux comin~ from a light source 8. ~uring the emission
of radiation, the irradiated element is Dlaced in
front of a metallic mirror 9 which is removed on
comDletion of the radiation process. Said element is
exposed to at least one monochromatic radiation at a
predetermined wavelength ~ ,
The wave of the luminuous flux 6 reflected from
the mirror 9 interferes with the incident wave whereby
standing waves are formed. The refractive index of the
light-sensitive material changes differently at
crests 10 and nodal points 11 of the standing waves.
After ex~osure to radiation, said element of
- 13
2~ 5
li~ht-sensitive material acquires the layer structu-
re 1. The crests 10 of said waves located equidistant-
ly in the irradiated element at a distance ~0~2n
from one another (where n is the re~ractive index
of the material) correspond to the equidistant layers
2 through 5 in the layer structure 1. So, the perio-
dicity of the layers 2 through 5 and, consequently,
the layer thickness d = ~ (1). Vertical lines
2n
mark schematically a plane 12, in which variations
of the refractive index of the light-sensitive mate-
rial are maximal, The number N of the layers 2
through 5 in the layer structure 1 depends on thick-
ness D of the irradiated element and on thickness d
of each layer 2 through 5 and is defined by the
equation
D D-2n
N = - Jlc (2~
Each layer 2 through 5 partially reflects lumi-
nous radiation directed to the layer structure. In-
terference of the beams reflected from the layers 2
throug~ 5 is maximal at a predermined wavelength
equal to the dif~erence between lengths of interfer-
ing beams, Radiation at said wavelength is filtered
by the proposed light filter upon reflection.
The irradiated element is made of a suitable
transparent light-sensitive material which may be
- 14
Z ~ 5
photoemulsion based on salts of silver or bichromi-
zed gelatin or a photorecording polymeric medium or
a photopolymerizing composition of materials,
The layer structure 1 comprises a base formed
with a prism 13 (~igure 2~ or an optical wedge 14
(~igure 3) or a lens 15 (~igure 4~.
In the prism 13 (~'igure 2~, the layer structure
1 is disposed on a reflective face 16, while luminous
radiation 17 is directed to any free face 18. ~iltered
10 radiation 19 comes out through another face 20 of the
prism 13.
Similarly, the layer structure 1 is arranged on
a face 21 (~igure 3) of the optical ~edge 14, the
luminous radiation 17 is directed to its face 22, and
15 the filtered radiation 19 comes out through the same
face 22.
When use is made of the lens 15 (~igure 4), the
light filter is designed in a manner similar to that
described above, It doe~ not only filter the radiation
20 17 but also brings it into a focus 23 of the lens 15
if the luminuous radiation 17 is collimated.
In all the embodiments described, radiation
24 (~igures 2 through 4~ reflected from the environ-
ment-light filter interface has a direction diffe-
25 rent from that of the filtered radiation 19.
The base may comprise more than one prism 13 orwedge 14, as illustrated in ~igures 5 and 6. Prisms
- 15
;~G~ ~8'
13' (and wedges 14'~ are arranged along the structu-
re 1 and their number depends on the length of the
structure 1. Each prism 13' has dimensions and,
consequently, weight much smaller than those in the
embodiment of ~igure 2, wherein only one prism 13 is
utilized. The weight and dimensions of all the prisms
13' are smaller than the weight and dimensions of the
prism 13.
Therefore, overall dimensions and total weight
of the light filter of Figure 5 are substantially
smaller than those in the embodiment of ~igure 2~ It
may be asserted that the construction of the entire
light filter is quasi-flat. The light filter is de-
signed in much the same manner in another embodiment
comprising a plurality of wedges 14' t~igure 6).
The irradiated element may be exposed to two or
more radiations at different wavelengths. Combi.na-
tions of equidistant layers corres~onding to said
wavelengths are formed in the element. Said combina-
tions of layers in the layer structure may be ar-
ranged differently to suit particular functions and
applications of the fabricated light filter.
Turning now to Figure 7 combinations 25 and
26 of the layers 2 through 5 and 2', 3', 4', 5' are
arranged successively in the direction of the radia-
tion 17 (~igure 2). The pro~osed light filter has
two ~lass bases 27 (Yigure 7) and 2~.
_ 16
Referring to ~igure 8 combinations 29, 30 and
31 are spatially separated along the layer structu-
re 1 made up of separate sections. Spatially separat-
ed are, accordingly, radiations 32, 33 and 3~ at
respective wavelengths ~ 2 and J 3
filtering by each combination 29 through 31, said
radiations bein~ derived due to the effect cf the
incident radiation on each secti~n of the structure l.
In ~igure 9 combinations 29', 30' and 31' of
said layers are spatially aligned. Spatially aligned
will be also radiations at respective wavelengths
~ 2 and /~3 after filtering by said combi-
nations.
~igure 10 shows diagramatically another embodi-
ment of the light filter whose production involves
exposure of said element to a continuous radiatlon
spectrum. In a layer structure 35, layers 2", 3", ~"
and 5" are arranged equidistantly in a cross-section
formed by a plane 36 perpendicular to one of the
layers 2" through 5" and to the direction, in which
the thickness of the layers 2" through 5" changes.
The thicXness of the layers 2" through 5" changes in
a monotone marner alon~ the layer structure 35. Such
a filter permits obtaining the a~alyzed radiation sEectrum
and continuously adjusting the wavelength of the
filtered radiation 17 (~i~ure 2~ by Moving it in
- 17
2~ 8
front of a slit diaphragm (not shown in the draw-
ing).
In another embodiment of the invention the light
filter having essentially the same capabilities comp-
rises the layer structure 1 (Figure 11) with a means37 for compressing said layer structure. Said compres-
sing means includes a cramp 38 and a screw 39 changing
the compressive force of the cramp 38. The layer
structure 1 is made of an elastic compressive mate-
rial, say bichromized gelatin.
After the layer structure 1 is compressed, itslayers 2" through 5" are equidistant (~igure 12) only
in a cross-section, similarly to the embodiment of
~igure 10.
In compliance with the invention the section of
the prism may represent a rhomboid 40 (~igure 13) or
anisosceles triangle 41 (~igure 14), which is a par-
ticular case of the rhomboid and is notj therefore,
considered. Two symmetrical side faces 42 (~igure 13)
and 43 of the rhomboid 40 accommodate two layer
structures 1 and ~4. The luminous radiation 17 is
directed to a free face 45, while the filtered ra-
diation 19 reflected successively from the layer
structures 1 and 44 comes out of another free face
46. An angle ~ between the free faces 45 and 46 is
chosen as follows:
_ 18
= 2~ if ~ ~ 90~
(3)
~ = 360 - 2~ if ~ ~90
where ~ is the angle between the faces 42 and 43
accommodating the layer structures 1 and 44, respec-
tively.
In a general case a prism 47 (~igure 15) i9 intri-
cately shaped and comprises at least two pairs of
respectively symmetrical side faces 48, 49 and 50, 51
with a common symmetr~ p~ane. One pair of said faces
48, 49 accommodates the layer structures 1, 44, and
the angles ~ and ~ between said pairs of the faces
48, 49 and 50, 51, respectively, are chosen by refe-
rence to equation (3). The luminous radiation 17
coming to the free face 50 is successively reflected
from the layer structures 44 and 1. The filtered ra-
diation 19 comes out of the free face 51.
Turning now to ~igure 16 the illustrated light
filter comprising the layer structure 1 disposed on
the prism 13 has a case 52 having an input hole 53
to pass the radiation 17 and a hole 54 al]o~ing exit
of the filtered radiation 19. The input hole 53 in
conjunction with holes 55 and 56 forms a di&phragm
which may be, for example,any light guide.
The layer structure 1 is arranged relative to
the emitted radiation 17 so tlat it may turn with
respect to the case 52 and also move linearly inde-
- 19
2~ 5
pendently or simultaneously. ~o accomplish this, the
prism 13 accommodating the layer structure includes
a turning mechanism comprising, for example, a worm-
-and-worm gear 57, 58 and a handle 59. The prism 13
5 is secured to the gear 57 of the worm set 57, 58. More-
over, the prism is linearly displaced by a screw 60
interacting with the gear 57 loaded with a spring 61.
The radiation 17 is transmitted through said
diaphragm formed by the holes 5~, 55, 56 to the prism
10 whereupon the filtered radiation comes out of the hole
54 on the opposite wall of the case 52.
The case 52' (~igure 17~ may be located beyond
the light filter, one of its walls serving as the
input face 16 of the prism 13. Arranged on the opposi-
15 te wall of the case 52' is the diaphragm formed bythe system comprising the holes 53, 55 and 56 in a
sleeve 63. ~he mechanism enabling linear displace-
ment of the prism 13 comprises a screw 64 and a spring
65, which interact with the sleeve 63 of the diaphragm
20 to provide for relative linear displacement of the
diaphragm and the prism 13. This is done to change
the angle of incidence of the radiation 17 directed
to the layer structure 1. The prism 13 secured to a
rotary base 66 is turned by changing the shape of the
25 case 52' representing bellows. The filtered radiation
19 comes out of the light filter through the face 20.
The selective interference light filter forming
- 20
2~ ~8 ~ S
the subject of the present invention operates in the
following manner.
The luminuous radiation 17 is directed to the
light filter and each layer 2 through 5 (Figure 2)
5 comprised in the layer structure 1 reflects a small
portion of said radiation. The reflected radiation
19 consists of a multitude of light beams characteriz-
ed by a constant difference in length, which depends
on the layer thickness d, the refractive index n
and the angle of incidence ~C of light directed to
the layer structure 1. The result of interference is
such that its peak is attainable only for the wave-
length ~ satisfying the following condition:
A = 2dn cos~C (4)
The wavelength of the reflected radiation 1
m~y be varied by changing the angle of incidence /~
of light directed to the light filter.
The light-sensitive material of the irradiated
element is chosen to be practically transparent to
radiation at the predetermined wavelength ~1O. The
refractive index of said material may vary slightly
under the action of light and its resolution should
be sufficient to provide for formation of a layer
structure (internal homogeneities within the material
should be smaller than /l/15).
- 21
In the light filter comprising a base, the ra-
diation 21 reflected from the air-filter interface is
linearly separated from the radiation 19 reflected
from the layers 2 through 5 or even has another direc-
tion. Hence, it does not interfere with the radiation19. Consequently, the interference pattern will not
be impaired.
If the base i9 a prism or an optical wedge, the
radiation 24 reflected from the air-filter interface
10 is separated angularly and the wavelength adjustment
range is wider than in the case of a plane-parallel
base.
When the lens 15 (~igure 4) is u~ed, the reflect-
ed radiation 19 has a peak at one wavelength, mono-
15 chromatic light being focused at the focal point23 of the lens 15 if a plane-parallel light beam is
incident on the light filter.
When the radiation 17 characterized by a conti-
nuous spectrum is incident on the light filter compris-
20 ing the combinations 25, 26, 29, 30 and 31 of saidlayers, it reflects two or more wavelengths. The wave~
may be spatially aligned (29', 30', 31'~ or separat-
ed (29, 30, 31).
When the radiation 17 is incident on different
25 sections of the light filter of ~igure 8 with layers
var~ing in thickness, different wavelengths ~ 1
/~ 2~ ~l3 are reflected.
The wavelength /1 of reflected light changes
z~ s
as the light filter and the incident beam of lumi-
nous radiation are displaced relative to each other
over a distance x without varying the angle of in-
cidence of the radiation directed to said light filter.
It is also possible to change the wavelength of reflec-
ted light by varying the angle of incidence of light
directed to said light filter. The light filter illust-
rated in ~igures 11 and 12 permits changing the value
d/l/dx, that is, di~persion thereof.
If the light filter o~ Figures 13 and 13 is affec-
ted by luminous radiation characterized by any spect-
rum and transmitted at any angle, said light filter
will reflect only one wavelength solely in case when
said wave affects the light filter at a predetermined
angle (parameters of the prism are chosen so as to
provide for separation of the radiation incident on
the light filter at right angles to the input face 31)~
The light filter of Figures 15, 16 and 17 gives
off solely the light incident thereon at right angleq
since the diaphragm (~`igures 16 and 17) does not
pass oblique beams. The light filter filters the
light at only one wavelength with the diaphragm and
the layer structure 1 relatively disposed in a prede~
termined manner. The light filter may be tuned to any
25 wavelength within a preset range by changing relati~e
position of said diaphragm and the layer structure 1.
~he orientation of the light filter is changed to
- 23
effect angle scanning, that is, to determine the
direction to the source of light (not shown in the
drawing) at a predetermined wavelength.
Given below are examples illustrating the use of
the preferred embodiments of the light filter.
Example 1
The selective interference light filter has a
layer structure of photoemulsion containing silver
bromide. The layer structure is 18 ~ thick. It con-
sists of at least 85 layers. The refractive index va-
ries from 1.52 to 1,60. Said layer structure is form-
ed by light emitted by a helium-neon (~e-Ne) laser at
the wavelength /~0 = 633 nm. The filtered radiation
has the wavelength A in the range from 480 to 633 nm.
The reflection factor is up to 40~o in the green
spectrum. The spectral bandwidth is within 8 - 10 nm
within the entire wavelength adjustment range.
Example 2
The selective interference light filter compris-
es a layer structure of bromated gelatin (with ammo-
nium bichromate). The layer structure is 10 ~ thick.
It consists of at least 60 layers. The re~ractive
index varies from 1.50 to 1.60. Said layer structure
is formed by light from an argon (Ar+) laser at the
wavelength /lo = 488 nm. The filtered radiation has
a wavelength in the range from 380 to 488 nm. The
- 2~ -
X ~ 85
reflection factor i9 Up to 70~o in the blue and greenregions of the spectrum. The spectral bandwidth is
within 5 - 6 nm.
xample 3
The selective interference light filter compris-
es a layer structure of a photorecording polymeric
medium representing an oxidizable recording medium
with anthracene. The layer structure is 1 mm thick.
It consists of at least 4500 layers. Said layer struc-
10 ture is formed by light from a helium-neon (He-Ne)
laser at the wavelength A 0 = 633 nm. The filtered
radiation has a wavelength in the range from 475 to
633 nm. The reflection factor is up to 10% in the
green spectrum. The spectral bandwidth is within
0.1 - 0.2 nm.
ExamPle 4
The selective interference light filter comp-
rises a layer structure of a liquid polymerizing
compound. The compound contains a radically polyme-
rized vinyl monomer and a stabilizing additive. ~he
layer structure is 20JU thick. Said layer structure
is formed by light from a helium-cadmium (~e-Cd)
laser at the wavelength /lo = 442 nm and consists
of about 130 layers. The filtered radiation has a
wavelength from 350 to 442 ~m. The reflection factor
is 15~ ~nd the spectral bandwidth is within 3 - 4 nm.
- 25
Z~8i~5
Exam~le 5
The selective interference light filter comp-
rises a layer structure of photoemulsion containing
silver bromide. The layer 3tructure is 21JU thick. It
consists of at least 100 layers. Said layer structure
is formed by light from a helium-neon (He-Ne~ laser at
the wavelength /~O = 633 nm. Said layer structure is
dispo~ed on the ~o~nu~e fa~e of a triang~r p~sm with a~ ~ 90
45 and 45 . The filtered radiation has a wavelength
10 in the range from 360 to 610 nm. The reflection factor
iq 40% or more in the red and violet qpectra and up to
70% in the green spectrum. The spectral bandwidth is
within 8 - 10 nm.
Example 6
The ~elective interference light filter comprises
a layer structure of photoemulsion containing silver
bromide. The layer structure is 21)u thick. It con-
sists of at least 100 layers. Said layer structure is
formed by light from a helium-neon (Ne--Ne) laser at
the wavelength ~0 = 633 nm. Said layer ~qtructure i~
disposed on the face of an optical wedge with an angle
of 30. The filtered radiation has a wavelength in
the range from 570 to 633 nm. The reflection factor
is about 60~.
Example 7
The selective interference light filter comprises
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~ 85
a layer structure of photoemulsion containing silver
bromide. The layer structure is 21JU thick. Said lay-
er structure is formed by light from a helium-neon
(,~e-Ne) laser at the wavelength i~ 01 = 633 nm in
5 one part of the photoemulsion plate and by light from
an argon (Ar+~ laser at the wavelength ~02 = 488 nm
in the other part of said photoemulsion plate.
The layer structure is disposed on a flat base.
The filtered radiation has two wave~ hs in a beam
of adjacent waves. If a screen is placed in the way
of said filtered radiation, the spot on the screen
will comprise two parts of different colours. As the
; angle of incidence of luminous radiation directed to
the light filter varies from 0 to +35, both wave-
lengths will change. More specifically, the shorter
wavelength will change from 380 to 488 nm and the
longer wavelength from 570 to 633 nm.
Exam~le 8
The selective interference light filter com~ris-
es a layer structure of photoemulsion containing sil-
ver bromide. The layer structure is 42 ~ thick. Said
layer structure is formed by radiation emitted by two
lasers having the wavelengths ~lo = 633 nm and
Ro = 488 nm. The layers formed by the first laser
occupy the first half of the plate in thickness. Con-
versely, the layers formed by the second laser occupy
the second part of the plate in thickness. The first
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2~
combination of layers is disposed ahead of the second
combination of layers in the way of radiation inci-
dent on said light filter. An analysis of the filtered
radiation sho~rs that it has two wavelengths at one
angle of incidence on said light filter. As the angle
of incidence changes, the filtered radiation wave-
lengths vary from 570 to 633 nm and from 350 to 488 nm
for /lo and /10, respectively.
Example 9
The selective interference light filter comprises
a layer structure of photoemulsion containing silver
bromide. The layer structure is formed by radiation
at the wavelength /lo = 633 nm and is disposed on both
legs of a triangular prisnl with angles 90, 45 and 45,
said prism being a particular case of a rhomboid. The
light filter is exposed to radiation from a source
characterized by a continuous spectrum. The filtered
radiation has a wavelength of 449 nm and a s~ectral
bandwidth of 10 nm. The filtration occurs only when
the radiation is normal to said light filter, As the
angle of incidence changes by 1, the intensity of
the filtered radiation decreases twice. The light
filter does not practically pass luminous radiation
when the angle of incidence changes by 2.
The proposed light filter is a selective narrow-
band filter adjustable in wavelengt'ns. Its production
is substantially simplified and the range of its uses
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~ 8 5
i9 increased, which is an apparent advantage over
the prior art.
~ he adjustable light filter having an adjust-
ment range within 240 nm at a ~pectral bandwidth of
8 nm can replace 30 unadjustable light filters having
the same spectral bandwidth. Considering the cost of
one light filter the invention can be very effective
economically,
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