JPS6162001A - Narrow band pass optical absorption filter - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical filter, in particular for absorbing optical radiation having a particular selected frequency within a narrow band and for absorbing optical radiation having a particular selected frequency outside said narrow band, but not The present invention relates to narrowband filters for effectively transmitting optical radiation having frequencies within a wider frequency band around a narrowband. Typically, the width of the narrow band is about 5-20 cm-' and the width of the wider band is about 200-1000 c+n-'.

Certain substances, particularly certain diatomic or polyatomic molecular ions, are typically found in matrix-separated spectral bands (m
atrix 1solation 5pectral
It is known to have a number of bands called bands. These ions form another substance, a solid solvent (
When dissolved within a crystal of a solid solvent, these ions form an impurity in the crystal, which is referred to as a "matrix" for the "isolated" molecular ions.

Since the spectral spectrum of a matrix-separated impurity ion is similar to the spectrum of a free molecular ion, the matrix spacing of molecular ions in ml is useful for analyzing the spectral yield characteristics of a particular impurity. Thus, molecular ionic impurities in the crystal? Analysis of its spectral properties is easy when the spectral properties are resolved, and such analysis has been described extensively in the literature.

Until now, the 718 Nox corner^11 absorption properties of substances in crystals have been determined by the optical hk II IJit 7! #ImatsuC, I think it was used as 1-7.

One object of the invention is to absorb optical radiation having a selected frequency t1, but within a frequency band containing the selected frequency i1! ! (7) 77! An object of the present invention is to provide an optical absorption filter that transmits fil rays.

One object of the present invention is to provide such a filter that transmits a high proportion of optical radiation within the frequency band of interest.

Yet another object of the invention is to provide such a filter in which the absorption frequency of impurities can be adjusted to match a selected lla frequency stop.

Summary of the One Shot-Decoy The present invention provides for absorbing optical radiation at a selected frequency and transmitting radiation at other frequencies within a selected frequency band that includes the selected frequency. A method for manufacturing a narrowband absorption filter is provided. This manufacturing method involves selecting an impurity with narrow-band absorption in the pendulum around the selected frequency band; Select a crystalline material that has substantial transparency.

adjusting the lattice constant of the crystal, thereby adjusting the absorption frequency Φ11 of the impurity to match the selected frequency, and filtering the impurity in the lattice constant adjusted crystal. Manufacture.

In a particular embodiment of the invention, lattice constant adjustment is achieved by producing a mixed crystal of two selected crystalline materials. In one example, the two substances have the same anion,
In another example, the two substances have the same cation. The absorption frequency of impurities can be lowered by replacing them with heavier ions in the mixed crystal. The absorption frequency of impurities can be increased by replacing them with lighter ions in the mixed crystal. The impurity is preferably a polyatomic ion that is resonant and causes narrow band absorption.

According to the present invention, a filter designed by the following method is provided.

According to the present invention, 55 to 95 atom % of the first alkali halide, 5 to 45 atom % of the second alkali halide, and 0
．． A material composition is provided that includes a mixed crystal having 25 to 5 atomic % impurities.

The alkali halides forming the mixed crystal can have either the same cation or the same anion. The impurity is cyanate ion, which can preferably be present in the range 0.5 to 3 atomic %.
can be. Other suitable impurities are perrhenate and chloride, acid salts.

One particular example is 5 to 35 atom % potassium bromide and 6
It has a material composition with 5 to 95 atom % of rubidium bromide and 0.5 to 3 atom % of cyanate ions as an impurity.

According to the invention, a narrow band filter for absorbing optical radiation of a selected frequency and transmitting optical radiation of other frequencies within a selected frequency band including the selected frequency. is provided. This filter consists of a mixed crystal with component crystalline material having a low average optical density over the frequency band. The mixed crystal has an impurity having a selected crystal component ratio and a narrow band spectral absorption characteristic at a frequency near the selected frequency. The crystal component ratio is selected to adjust the lattice constant of the mixed crystal and thereby the spectral absorption properties of the impurity to the selected frequency.

The mixed crystal is preferably an alkali halide mixed crystal having either two components having the same anion or two components having the same cation. The impurities can be polyatomic ions such as cyanate or perrhenate ions.

According to the invention, fluorinated water with a wavelength of 2.911 μm
A narrow band filter is provided in the IP for absorbing radiation from the elementary laser and transmitting radiation in a surrounding frequency band with a high transmission ratio. The filter contains an alkali halonide crystal with optically incident and transmitting surfaces and an impurity of about 1 atomic percent cyanate ion.

Suitable alkali monophosphates for use in narrowband filters include potassium bromide, rubidium bromide, and potassium iodide. Crystal cores can be mixed crystals with multiple alkali halides, such as potassium bromide and potassium iodide, or potassium bromide and rubidium bromide.

According to the invention, a narrow band filter for absorbing radiation from a carbon dioxide laser with a wavelength of I O,59/I m and transmitting Ji (184 cotton) with a high transmission ratio in the surrounding frequency band is provided. The second filter is provided with an optically incident, one, and a transmitting surface) with an alkali halogenide crystal and about 1 atomic percent of an acid ion or an acid ion. Contains impurities.

A suitable alkali halide for this crystal: 1,
Contains thorium bromide, potassium bromide, and lithium bromide. This crystal is a mixed alkali halide crystal, such as potassium bromide and bromide l-1J or
-S117 and lithium bromide.

According to the invention, a narrow band is provided for selectively absorbing optical radiation of a desired frequency within the frequency band and transmitting optical waves of other frequencies within the frequency band. An absorption filter is provided. This filter consists of selected impurities within selected crystals. The impurity is narrowly isolated at the desired frequency within the crystal by 7-trisox absorption↑
'l and crystallize with substantial transparency within the selected frequency band.

The selected impurities can include minority atom elements such as oxygen 18 in the siebate ion impurity.

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the invention as well as other objects of the invention, the invention will now be further described with reference to the accompanying drawings. In addition, the scope of the present invention is indicated in the scope of claim 4 and claim + (i).

Optical Fatigue Figure 1 shows an optical system, such as an infrared detection system, using the filter 10 of the present invention. The system of FIG. 1 includes a detection device 12, such as an infrared camera, used for the detection of infrared radiation or other optical frequency radiation emitted from radiation-fi 14. FIG. 1 shows an apparatus 1 for detecting radiation from a radiation source 14.
Also shown is a laser 16 that emits laser radiation 20 that can seriously interfere with detection by 2. Filter 10 of FIG. 1 has optically incident and transparent surfaces and is adapted to transmit most of the relatively broadband radiation from radiation source 14, represented by wave 18, and to absorb single frequency radiation from the laser. It is designed to. Thus,
The use of the filter IO makes it possible to specifically filter out interfering laser radiation and to detect radiation within the same frequency band emitted by the radiation source 14.

/ To achieve the purpose of the filter 10 shown in FIG. 1, the filter must have the transmittance characteristics shown in the graph of FIG. For example, the radiation detection device 12 is configured to receive and receive infrared rays having a wave number of about 3300 to 3700 cm-'. Therefore, it is desirable to have a relatively flat and high transmittance over the frequency band shown by the flat top 22 of the transmittance curve shown in FIG. In order to filter out narrowband radiation from the laser 16, which is assumed to have a transmission frequency indicated by cotton 24 in FIG. have. Thus, most of the desired broadband radiation from the radiation source 14 is transmitted through the filter 10 and is received by the detection device 12, whereas the low frequency or narrow band radiation from the laser 16 is mostly absorbed by the filter 10. and does not interfere with the operation of the detection device W12.

As mentioned above, certain substances, among others cyanates, perrhenates, cyanides, nitrites, carbonates, bicarbonates, azides, hydrofluoride (HFz), hydroxides compound, ammonia compound (aIIlmoniate)
), boron hydrite,
Polyatomic ions such as chromate and borate are known to have narrow spectral absorption properties at individual frequencies that include the frequency of interest in the infrared spectrum. These frequencies are very often measured in isolation matrix measurements, in which case the spectral properties of an impurity such as an ion can be determined by comparing a small amount, e.g. 0.1 atomic %, of an impurity with another It is measured by placing it in a crystal of a substance. As used herein, the term ``atomic percent'' means the percentage of a particular substance in a crystal compared to the number of ions of a similar substance.Thus, the atomic percent of an alkali halide salt is By atomic percent of an ion is meant the ratio of the number of atoms of a particular type of ion, such as an anion or anion, to the total number of ions in the crystal. To date, such isolated 7-trinox measurements of crystalline impurities have been made for the purpose of scientific research and evaluation, and no practical application of such isolated matrix absorption properties is known.

The present invention (, 1, very often narrowband impurity isolation matrix absorption is received by the detection device 1) 1 ■ 1
It is a result of the inventors' discovery that narrowband filters can be used for another purpose, to filter out undesired interfering 1.1 lines from broadband radiation that is transmitted.

As an example, we have shown that interference radiation from a hydrogen fluoride (I(S)) laser with a wavelength of 2.911 μm (wavenumber 3435 cm-') can be filtered out from other radiation in the surrounding infrared spectrum. investigated the possibility of manufacturing a narrowband absorption filter for the purpose of HF lasers.As mentioned above, the desired transmission characteristics of such a filter for HF lasers are shown in the graph of FIG.

In researching materials for absorbing HF laser radiation, radiologists have discovered that cyanate ions (NGO-') have a desired wavenumber of 34.
It was found that the absorption characteristics are very close to 35 cm. Cyanate ion is 344% in potassium bromide crystals.
2 cm-', 3432 cm-' in rubidium bromide crystal
has an absorption line.

Although cyanate ions in pure crystals such as potassium bromide and rubidium bromide have sufficiently broad spectra with high impurity doping to give substantial absorption 1f+ at the frequencies of interest, the present invention We have discovered that by adjusting the lattice constant of the crystal, the absorbance of cyanate ions relative to the frequency of the hydrogen fluoride laser can be further improved. One way to adjust the lattice constant is through the use of mixed crystals, such as mixed crystals of rubidium bromide and potassium bromide, potassium bromide and potassium iodide, thallium bromide and thallium chloride, or cesium chloride and cesium bromide. Such mixed crystals allow adjustment of the lattice constant of the crystal, thereby adjusting the absorption frequency of impurities.

With respect to lattice constant adjustment, we have discovered that a larger average lattice constant, produced, for example, by substituting heavier ions within the crystal, lowers the absorption frequency of impurities. The natural result from Gore is also true.

That is, replacing lighter ions within the crystal gives a smaller lattice constant and increases the absorption frequency of the impurity.

The variation in lattice constant and absorption frequency of I cyanate at the frequency of interest is shown in graph 28 of FIG. This graph shows absorption frequencies for lattice constants corresponding to potassium chloride, potassium bromide, and potassium iodide. This figure shows 60 atom % potassium bromide, 39 atom % potassium iodide and approximately 1 atom % cyanate ion doping (1% replacement of bromine and iodine anions by cyanate ions). Also shown is the absorption frequency of the potassium bromide-potassium iodide mixed crystal. This mixed crystal has an absorption frequency exactly at the hydrogen fluoride Lely' frequency of interest.

EXAMPLE A mixed crystal consisting of 60 atom % potassium bromide, 39 atom % potassium iodide and 1 atom % cyanate ion was prepared as follows.

A mixture of molten potassium bromide and potassium iodide having a distribution ratio of - was mixed with potassium cyanate at a ratio of 1 atomic % to introduce cyanate ion impurities.

The crystal is grown using the Czochralski method. This crystal has a wavelength of 2.6 at a wave number of 3435 cm-', which corresponds to the radiation frequency of a hydrogen fluoride laser.
It had an optical density of /can. This crystal is 330
Approximately 90% over the frequency range from 0 to 3700 cm-'
It had an optical transmission ratio of .

Crystals were prepared consisting of 10 atom % potassium bromide, 89 atom % rubidium bromide and 1 atom % cyanate ion in the form of potassium cyanate.
The crystals were grown using the Alski method.

As a result of measuring the optical properties of the crystal, this crystal is 3435c
It had a sharp absorption line with an optical density of 2.6/cm for the radiation of m= and a transmission of about 92% over the frequency band of interest from 3300 to 3700 cn+-'.

Those skilled in the art will recognize that the transmittance of the crystals listed above can be improved by coating the crystals with suitable materials.

The ratio of the component crystalline materials for the mixed crystal is selected to tune the impurity absorption frequency to the desired frequency, as explained with respect to FIG. 3, but in the case of the alkali halide mixed crystal. A crystal having a component crystal ratio of a two-component crystal material in the ring part may have an adverse effect on the stability of the crystal, so it is preferable to use a cell. Thus, such alkali halide mixed crystals: 1, generally 55 to 95 atom % of the first
It is composed of a component crystalline material and 5 to 45 atom % of a second crystalline material. It is thought that the ratio of 5 atomic % of the ungrooved second crystal material has almost no tuning effect.

The optical density of the filter is largely determined by the amount of impurities introduced. As shown in the examples, an amount of 1 atomic % provides a good optical density at the absorption frequency (2, f', /cm).
Therefore, a filter with an optical density of 4 can be manufactured with a transmission length of less than 2 can.

If a lower optical absorption density is required, lower impurity percentages can be used, such as 0.25 or 0.5 atomic %. Higher impurity percentages give higher optical densities at absorption frequencies, but impurity percentages greater than 2 at.%, e.g. Broadens absorption lines that fall at other spectral absorption frequencies of impurities. Although this broadening can be beneficial if the absorption frequency is not exactly the desired frequency, or if more broadband interference is expected, it adversely affects the average optical transmission of the filter over the band in question.

Experiments have shown that increasing the amount of doping material to 5% causes broadening of the absorption frequency, which may adversely affect the broadband transmission characteristics of the filter.

The possibility of a similar narrowband absorption filter for absorbing carbon dioxide lasers at wavelengths of 10.59 μm was investigated. Research has shown that perrhenates are suitable for absorbing radiation at this frequency. Also,
Similarly, crystals for use with perrhenate ions include sodium bromide, potassium bromide J1, lithium bromide,
Contains potassium chloride and cesium chloride. Combination crystals with components of sodium bromide and potassium bromide, sodium bromide and lithium bromide, or potassium chloride and cesium chloride probably have a suitable lattice constant adjustment through the formation of mixed crystals. will give you the possibility. Other possible impurities for absorbing carbon dioxide laser radiation are bicarbonates, chromates.

I 0.59μm using chromate ion as impurity
An absorption filter for carbon dioxide laser radiation is shown in the example below.

Dashi Lian 1. U- A crystal consisting of 75 atom % of potassium chloride, 22.41 atom % of potassium bromide, 1.59 atom % of lead chloride, and 11 atom % of potassium J chromate was produced. Crystals were grown using the Czochralski method.

This crystal showed an optical absorption corresponding to an optical density of l/cm at I 0.59 μm and high transmittance at frequencies around that. In this crystal, lead chloride was added for crystal charge compensation to provide electrical balance and crystal stability. Absorbable impurities are chromate ion impurities.

1? In this embodiment, the adjustment of the absorption frequency is achieved by adjustment of the crystal lattice constant. Another possible regulation mechanism is to vary the isotopic content of the impurities.

Thus, by dissolving the isotopic cyanate 14N12cIIlo in the crystals of pure potassium chloride, 2. Q
ll, +rm If F l/- absorbent filter for cotton can be manufactured. This isocyanate has a minority oxygen 18 isotope and gives a different absorption frequency than the natural oxygen 16 isotope.

While research has so far focused on the absorption of special laser radiation within the infrared frequency spectrum, the principles of the present invention
It is applicable to the absorption of unwanted radiation at visible light frequencies through the use of electronic transition spectral absorption characteristics rather than the mechanical ion vibrational absorption spectral characteristics typical of the previously described infrared filters. Adjustment of the crystal lattice constant is thought to be done by adjusting the absorption number by changing the electric field environment of the impurity/f-on. A similar adjustment of the electric field environment of atomic impurities with suitable transition electron spectroscopic absorption properties, such as transition metals,
Perhaps it could be used to tune the absorption frequencies of impurity atoms with the aim of obtaining narrowband filters operating within the visible frequency band.

1) Although we have described what we believe to be the preferred embodiments of the present invention above, those skilled in the art will be able to make other changes and modifications to these embodiments without departing from the spirit of the invention. You will recognize that you can make the following changes. All such variations are intended to fall within the true scope of this invention.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a system using the filter of the present invention. FIG. 2 is a graph showing the spectral transmission characteristics of the filter of FIG. 1. FIG. It is a graph shown as a function of a constant. Brief explanation of the drawings 10... Filter 12... Detection device 14.
...Radiation source 16...Laser 18...Wave 20...Laser beam]' Continuation Amendment (Method) Showa year, month, day 1, case record 1975 patent application No. 18022
No. 6 2, Title of the invention Narrowband optical absorption filter 3, ? Relation to the case of the person making the request to stop the agency 4. Subject of the amendment to the agent Separate document certifying authority of representation Full drawings 18 7. Contents of the amendment An engraving of the drawings as shown in the attached sheet (no changes to the contents) - 〇－

Claims (41)

[Claims] (1) A method for making a narrow band absorption filter for absorbing optical radiation of a desired frequency and transmitting optical radiation of other frequencies within a selected frequency band that includes the desired frequency. selecting an impurity that has narrow band absorption in the crystal at a frequency near the desired frequency; and matrix isolation absorption characteristics for the impurity to have narrow band absorption above the desired frequency. selecting a first crystalline material having a matrix isolation absorption property for the impurity to have a narrow band absorption below the desired frequency; and selecting a second crystalline material having substantial transparency over the selected frequency band and crystal forming compatibility with the first selected crystalline material; selecting the ratio of the first crystal to the second crystal to adjust to a desired frequency; the selected ratio of the first crystal material to the second crystal material and the selected amount of the impurity; A manufacturing method consisting of a step of manufacturing a filter consisting of a mixed crystal of. (2) The manufacturing method according to claim (1), wherein the second crystal material selection step includes selecting a second crystal material having the same anion as the first crystal material. (3) The manufacturing method according to claim (1), wherein the second crystal material selection step includes selecting a second crystal material having the same cation as the first crystal material. (4) The production method according to claim (1), wherein the impurity is selected from the group consisting of polyatomic ions. (5) The manufacturing method according to claim (4), wherein the impurity ions are selected to have narrow band absorption properties consisting of mechanical resonance. (6) A filter manufactured by the method described in claim (1). (7) A substance consisting of a mixed crystal containing selected impurities, the mixed crystal comprising 55 to 95 atom % of a first alkali halide, 5 to 45 atom % of a second alkali halide, and 0.5 to 95 atom % of a second alkali halide.
25 to 5 atom % of said impurity. (8) The substance according to claim (7), wherein the first and second alkali halides have a common cation. (9) The substance according to claim (7), wherein the first and second alkali halides have a common anion. (10) The substance according to any one of claims (7) to (9), wherein the impurity is a cyanate ion. (11) The substance according to claim (10), which contains 0.5 to 3 atomic % of impurities. (12) The substance according to any one of claims (7) to (9), wherein the impurity is a perrhenate ion. (13) The substance according to any one of claims (10) to (12), wherein the impurity is a chromate ion. (14) A substance consisting of a mixed crystal and an impurity, the mixed crystal containing 5 to 15 atom% of potassium bromide, 85 to 95 atom% of rubidium bromide, and 0.5 to 3 atom% of impurities. A substance consisting of cyanate ions. (15) A substance consisting of a mixed crystal and an impurity, the mixed crystal comprising 55 to 65 atom% of potassium bromide and 35 to 45 atom% of potassium bromide.
of potassium iodide and 0.5 to 3 atom % of cyanate ions as impurities. (16) A substance consisting of a mixed crystal and an impurity, the mixed crystal comprising 69 to 80 atom% potassium chloride and 17 to 30 atom%
of potassium bromide and 0.5 to 3 atom % of chromate ions as impurities. (17) A material according to claim (16) which also contains up to 3 at. % lead chloride. (18) A narrow band filter for absorbing optical radiation at a desired frequency and transmitting optical radiation at other frequencies within a selected frequency band that includes the desired frequency, the filter comprising:
a mixed crystal having a component crystalline material having a low average optical density over the frequency band, a selected crystal component ratio, and an impurity within the crystal having narrowband spectral absorption characteristics at frequencies near the desired frequency; a narrow band filter that selects the crystal component ratio to adjust the lattice constant of the mixed crystal, thereby adjusting the impurity spectral absorption characteristic to the desired frequency. (19) The narrow band filter according to claim (18), wherein the component crystalline substance is an alkali halide. (20) The narrow band filter according to claim (18) or (19), wherein the component crystalline substances have the same anion. (21) A narrow band filter according to claim (18) or (19), wherein the component crystalline substances have the same cations. (22) The narrow band filter according to claim (18) or (19), wherein the impurities are polyatomic ions. (23) The narrow band filter according to claim (22), wherein the impurity is a perrhenate ion. (24) The narrow band filter according to claim (22), wherein the impurities are cyanate ions. (25) The narrow band filter according to claim (22), wherein the impurities are chromate ions. (26) A narrow band filter for absorbing radiation from a hydrogen fluoride laser at a wavelength of 2.911 μm and for transmitting radiation in an ambient frequency band with a high transmission ratio, comprising an optically incident and transmitting surface. a narrow band filter comprising an alkali halide crystal having a nitride and an impurity of about 1 atom % of cyanate ions. (27) The alkali halide crystal is made of an alkali halide selected from the group consisting of potassium bromide, rubidium bromide, and potassium iodide.
Narrowband filter described in ). (28) The narrow band filter according to claim (26), wherein the alkali halide crystal is a mixed alkali halide crystal having a plurality of component crystal substances. (29) A narrow band filter according to claim (28), wherein the component crystalline substance comprises potassium bromide and potassium iodide. (30) A narrow band filter according to claim (28), wherein the component crystalline substance comprises potassium bromide and rubidium bromide. (31) A narrow band filter for absorbing radiation from a carbon dioxide laser at a wavelength of 10.59 μm and for transmitting radiation in an ambient frequency band with a high transmission ratio, comprising a plurality of component crystalline materials and an optical A narrowband filter comprising a mixed alkali halide crystal having incident and transmitting surfaces and an impurity of about 1 atomic percent perrhenate ion. (32) A narrow band filter according to claim (31), wherein the component crystalline substance comprises potassium bromide and sodium bromide. (33) A narrow band filter according to claim (31), wherein the component crystalline substance comprises sodium bromide and lithium bromide. (34) A narrow band filter according to claim (31), wherein the component crystalline substance comprises potassium chloride and cesium chloride. (35) A narrow band filter for absorbing radiation from a carbon dioxide laser at a wavelength of 10.59 μm and for transmitting radiation in an ambient frequency band with a high transmission ratio, the filter having optical entrance and transmission surfaces. A narrow band filter containing an alkali halide crystal and an impurity of about 1 atom % of chromate ions. (36) The narrow band filter according to claim 35, wherein the alkali halide crystal is a mixed alkali halide crystal having a plurality of component crystal substances. (37) A narrow band filter according to claim (36), wherein the component crystalline substances are potassium chloride and potassium bromide. (38) The narrow band filter according to claim (37), wherein the alkali halide crystal also contains lead chloride. (39) within a selected crystal for selectively absorbing optical waves of a desired frequency within a selected frequency band and transmitting optical waves of other frequencies within the frequency band; a narrowband absorption filter comprising a selected impurity having a selected minority isotope element and a narrowband isolation matrix absorption at the desired frequency within the crystal; a narrowband absorbing filter having substantial transparency within the selected frequency band. (40) The narrow band filter according to claim (39), wherein the impurity is a cyanate having an oxygen-18 minority isotope. (41) Claim No. (41) wherein the crystals contain potassium chloride
40) The narrowband filter described in item 40).