JP4863174B2 - Light reflecting film and laser oscillation element using the same - Google Patents

Description

  The present invention relates to a light reflection film and a laser oscillation element using the same, and more particularly to a light reflection film using a cholesteric liquid crystal layer and a laser oscillation element using the same.

A cholesteric liquid crystal has a property of selectively reflecting light in a specific wavelength range, and selectively reflects light in a specific wavelength range when white light is incident. For this reason, the cholesteric liquid crystal layer can be used as a reflection plate of a liquid crystal display or a projection screen itself (see, for example, Patent Document 1).
JP 2005-106945 A

  By the way, when the cholesteric liquid crystal layer is used as a reflector of a liquid crystal display or the projection screen itself, the cholesteric liquid crystal layer is desired to reflect white light when white light is incident. However, in general, the wavelength range of light selectively reflected by the cholesteric liquid crystal layer does not cover the entire wavelength range of visible light. That is, the selective reflection bandwidth of the cholesteric liquid crystal layer is determined by the product of the helical pitch P and the birefringence Δn, and generally does not exceed 150 nm and does not reach about 400 nm in the visible light region of 400 nm to 800 nm. . Therefore, in order to realize a light reflecting film that selectively reflects the entire wavelength range of visible light, that is, a light reflecting film that reflects white light by incidence of white light, three or more kinds of cholesteric liquid crystal layers having different helical pitches are used. Need to be laminated.

  However, when such a cholesteric liquid crystal layer laminate is used as a light reflecting film, it is necessary to increase the thickness of each cholesteric liquid crystal layer in order to reflect a sufficiently strong white light. Will increase as a whole. On the other hand, when the thickness of the light reflecting film is decreased, the reflected light intensity is weakened.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a light reflecting film capable of reflecting white light with sufficient intensity even when thin, and a laser oscillation element using the same.

  In order to solve the above problems, the present invention includes a plurality of cholesteric liquid crystal layers including cholesteric liquid crystals and an isotropic layer provided between the adjacent cholesteric liquid crystal layers and made of an isotropic medium. The cholesteric liquid crystal layer in the cholesteric liquid crystal layer has a spiral pitch number of 2 or less and has the same handedness of the spiral, the cholesteric liquid crystal layers in the plurality of cholesteric liquid crystal layers have the same spiral pitch, and the cholesteric liquid crystal layer The selective reflection band has a central wavelength of 500 to 560 nm, and the thickness of the isotropic layer is greater than 0.3 μm.

  According to this light reflecting film, even when it is thin, white light can be reflected with sufficient intensity when white light is incident.

Usually, as in the light reflecting film having the above-described configuration, only light in a specific wavelength region is selectively reflected when the spiral pitch and spiral hand of the plurality of cholesteric liquid crystal layers are the same. Moreover, as described above, the wavelength band of selective reflection generally does not exceed 150 nm. Therefore, it should be difficult to reflect white light even if white light is incident on the light reflecting film having the above-described configuration. In addition, if the thickness of each cholesteric liquid crystal layer is reduced to reduce the thickness of the entire light reflecting film, the reflected light intensity from each cholesteric liquid crystal layer will decrease, so the reflected light intensity of white light should decrease. is there.

  However, according to the light reflecting film of the present invention, when white light is incident, it is possible to reflect white light even though the spiral pitch and spiral nature of each cholesteric liquid crystal layer are the same. . Specifically, according to the light reflecting film of the present invention, the selective reflection wavelength band centered on the blue wavelength, the selective reflection wavelength band centered on the red wavelength, and the selective reflection wavelength band centered on the green wavelength. And at least appear, and as a result, incident white light can be reflected as white light.

  Moreover, even if the thickness of each cholesteric liquid crystal layer is reduced, white light can be reflected with sufficient intensity.

  The reason why such an effect is obtained is not clear, but it is thought that the light reflecting film of the present invention acts as a one-dimensional photonic crystal having a defect mode as a whole by having the above configuration.

  In addition, when the number of spiral pitches of the cholesteric liquid crystal exceeds 2, coloring occurs. On the other hand, if the film thickness of the isotropic layer is 0.30 μm or less, the number of peaks in the reflection spectrum is reduced and whitening does not occur. Further, coloring occurs even when the central wavelength of the selective reflection band of the cholesteric liquid crystal itself of each cholesteric liquid crystal layer is out of 500 to 560 nm.

  In addition, the present invention provides a first and second light reflecting films disposed opposite to each other, and a different light medium provided with an anisotropic medium provided between the first light reflecting film and the second light reflecting film. An anisotropic medium layer, wherein the first and second light reflecting films are the light reflecting films, and the first light reflecting film, the anisotropic medium layer, and the second light reflecting film are At least one of the layers contains a dye that emits fluorescence by photoexcitation, and the peak in the reflection spectrum of the first light reflection film and the peak in the second reflection spectrum overlap in the wavelength region of visible light. A laser oscillation element in which the emission band of fluorescence emitted from the dye is in the wavelength region of visible light.

  According to this laser oscillation element, as the first light reflecting film and the second light reflecting film, a light reflecting film capable of reflecting white light with sufficient intensity even if thin is used. Accordingly, when the laser oscillation element is irradiated with light that excites the dye, three or more oscillation peaks can be observed in the wavelength region of visible light. For this reason, by using a filter that selectively cuts a specific wavelength, it is possible to extract light of an arbitrary wavelength among a plurality of wavelengths corresponding to three or more oscillation peaks even though it is a single laser oscillation element. The range of selection for the wavelength of light to be extracted can be expanded. According to the laser oscillation element, white light can also be laser-oscillated when three or more oscillation peaks are distributed in the vicinity of each of the blue wavelength, the green wavelength, and the red wavelength. Furthermore, according to the laser oscillation device of the present invention, the number of oscillation peaks can be adjusted by adjusting the irradiation energy of the light that excites the dye, and thereby the oscillation wavelength can be controlled. In this case, since it is not necessary to use a filter as described above, a wavelength tunable laser oscillation element can be realized with a simple optical system. Furthermore, even if the first light reflecting film and the second light reflecting film are thin, sufficient white light can be reflected. Therefore, the first light reflecting film and the second light reflecting film can be made thin, and thus the laser oscillation element can be made compact. Can be achieved.

  In this specification, “white” is indicated by coordinates inside a circle with a radius of 0.05 centered on the white origin (0.3127, 0.3290) in the D65 light source in the xy color coordinates. I will say things.

Further, in the present invention, in the spectrum obtained by measuring the transmission spectrum of the cholesteric liquid crystal with a microscope spectrum meter (ORC-made TFM-120AFT-PC), two wavelengths having a transmittance of 60% in the selective reflection band. The wavelength on the short wavelength side is the “short wavelength end of the selective reflection band”, the wavelength on the long wavelength side is the “long wavelength end of the selective reflection band”, and the value obtained by calculating the average of them is the This is called the center wavelength.

  ADVANTAGE OF THE INVENTION According to this invention, even if it is thin, the light reflection film which can reflect white light with sufficient intensity | strength, and a laser oscillation element using the same are provided.

  Hereinafter, embodiments of the present invention will be described in detail.

(Light reflecting film)
FIG. 1 is a side view showing a preferred embodiment of the light reflecting film according to the present invention. As shown in FIG. 1, the light reflecting film 10 of this embodiment includes two cholesteric liquid crystal layers 1 and 2, and an isotropic layer 3 is provided between adjacent cholesteric liquid crystal layers 1 and 2. . Specifically, the isotropic layer 3 is sandwiched between the cholesteric liquid crystal layers 1 and 2 and is in close contact with each of the cholesteric liquid crystal layers 1 and 2. The cholesteric liquid crystal layer 1 is provided with an alignment substrate 4 on the side opposite to the isotropic layer 3, and the alignment substrate 4 is in close contact with the cholesteric liquid crystal layer 1.

  In the cholesteric liquid crystal in the cholesteric liquid crystal layers 1 and 2, a spiral structure is formed by liquid crystal molecules. Specifically, the direction of the director of the liquid crystal molecules changes so as to spiral along the thickness direction of the cholesteric liquid crystal layers 1 and 2, in other words, along the direction perpendicular to the surfaces of the cholesteric liquid crystals 1 and 2. is doing. The cholesteric liquid crystal can selectively reflect light in a specific wavelength band due to this helical structure.

  Here, the spiral pitches of the cholesteric liquid crystals of the cholesteric liquid crystal layers 1 and 2 are the same, and the handedness of the spirals is also the same. Specifically, in the present embodiment, the palm of the cholesteric liquid crystal layers 1 and 2 is on the left. The spiral axes of the cholesteric liquid crystals of the cholesteric liquid crystal layers 1 and 2 are parallel to each other. The pitch of the spiral of the cholesteric liquid crystal is 2 or less, and the center wavelength of each selective reflection band of the cholesteric liquid crystal layers 1 and 2 is 500 to 560 nm.

  The isotropic layer 3 is composed of an isotropic medium. The isotropic medium is not particularly limited as long as it is an isotropic medium. However, the isotropic medium has a property that it can be dissolved in a solvent that does not dissolve the cholesteric liquid crystal layers 1 and 2 and can impart alignment ability to the cholesteric liquid crystal. It is preferably an optically isotropic material having a refractive index smaller than about 1.55. As such an isotropic medium, for example, polyvinyl alcohol (PVA) can be preferably used. This is because polyimide and the like are colored yellow due to absorption on the short wavelength side, whereas PVA is almost completely transparent and easily reflects white light.

  The thickness of the isotropic layer 3 is greater than 0.3 μm. The thickness of the isotropic layer 3 is preferably 0.35 to 1.5 μm because the number of reflection peaks is 3 or more.

  According to the light reflecting film 10, white light is vertically incident on the surface of the cholesteric liquid crystal layer 2 from the cholesteric liquid crystal layer 2 side, for example. Then, although the cholesteric liquid crystal layers 1 and 2 have the same spiral pitch and spiral hand, white light can be reflected. Specifically, according to the light reflecting film 10, the selective reflection wavelength band centered on the blue wavelength, the selective reflection wavelength band centered on the red wavelength, and the selective reflection wavelength band centered on the green wavelength. It appears at least and reflects the incident white light as white light.

  In addition, white light can be reflected with sufficient intensity even if the thickness of each cholesteric liquid crystal layer 1, 2 is reduced. In other words, when one of the cholesteric liquid crystal layers 1 and 2 is different from the spiral pitch of the other cholesteric liquid crystal layer while keeping the thickness of the light reflecting film 10 constant. In comparison, the incident white light can be reflected as white light having a sufficient intensity. Further, in the above embodiment, even if there are two cholesteric liquid crystal layers 1 and 2, the incident white light is reflected as white light. Therefore, the light reflecting film 10 of this embodiment is sufficient for thinning the light reflecting film. Can contribute.

  Next, the cholesteric liquid crystal layers 1 and 2 will be described in detail.

(Cholesteric liquid crystal)
The cholesteric liquid crystal contained in the cholesteric liquid crystal layers 1 and 2 is not particularly limited as long as the center wavelength of the selective reflection wavelength band is 500 to 560 nm. The liquid crystal materials constituting such cholesteric liquid crystals include high-molecular liquid crystal materials and low-molecular liquid crystal materials. Examples of high-molecular liquid crystal materials include various main-chain liquid crystal materials, side-chain polymer liquid crystal materials, Alternatively, a mixture thereof can be used.

  Main chain polymer liquid crystal materials include polyester, polyamide, polycarbonate, polyimide, polyurethane, polybenzimidazole, polybenzoxazole, polybenzthiazole, polyazomethine, polyesteramide, polyester carbonate Polymer liquid crystal substances such as polyester and polyesterimide, or mixtures thereof.

  Further, as the side chain type polymer liquid crystal substance, a substance having a skeleton chain of a linear or cyclic structure such as polyacrylate, polymethacrylate, polyvinyl, polysiloxane, polyether, polymalonate, polyester, etc. In addition, a polymer liquid crystal substance in which a mesogen group is bonded as a side chain, or a mixture thereof.

  Among these, a main chain type polymer liquid crystal substance is preferable from the viewpoint of easiness of synthesis and orientation, and among them, a polyester type is particularly preferable.

  Preferred examples of the polymer structural unit include aromatic or aliphatic diol units, aromatic or aliphatic dicarboxylic acid units, and aromatic or aliphatic hydroxycarboxylic acid units.

  Low molecular liquid crystal substances include saturated benzene carboxylic acid derivatives, unsaturated benzene carboxylic acid derivatives, biphenyl carboxylic acid derivatives, aromatic oxycarboxylic acid derivatives, Schiff base derivatives, bisazomethine compound derivatives, azo compounds. Derivatives, azoxy compound derivatives, cyclohexane ester compound derivatives, sterol compound derivatives, etc., a compound exhibiting liquid crystallinity introduced with a reactive functional group at the terminal, or a compound exhibiting liquid crystallinity among the above compound derivatives And a composition to which a functional compound is added.

(Oriented substrate)
The alignment substrate 4 is not particularly limited as long as it is transparent and can support the cholesteric liquid crystal layer 1. Examples of the alignment substrate 4 include polyimide, polyamide, polyamideimide, polyphenylene sulfide, polyphenylene oxide, polyphenylene oxide, and the like. Ether ketone, polyether ether ketone, polyether sulfone, polysulfone, polyethylene terephthalate, polyethylene naphthalate, polyarylate, triacetyl cellulose, epoxy resin, phenol resin film, etc., or uniaxially stretched or biaxially stretched of these films Examples thereof include a film or a glass substrate. Some of these films exhibit sufficient alignment ability with respect to the cholesteric liquid crystal used in the cholesteric liquid crystal layer 1 without performing processing for expressing the alignment ability again depending on the manufacturing method, but the alignment ability is not satisfactory. In the case where it is not sufficient or does not show orientation ability, if necessary, these films are stretched under appropriate heating, the film surface is rubbed in one direction with a rayon cloth or the like, or a so-called rubbing treatment is performed on the film. Provide an alignment film made of a known alignment agent such as polyimide, polyvinyl alcohol, silane coupling agent, etc. and perform rubbing treatment, oblique vapor deposition treatment of silicon oxide or the like, or appropriately combine these treatments You may use the film which expressed orientation ability. Various glass plates having regular fine grooves on the surface can also be used as the alignment substrate 4.

  Among these, the alignment substrate 4 is preferably formed by forming a rubbing alignment film (for example, polyvinyl alcohol) on a film.

(Method for producing light reflecting film)
Next, the manufacturing method of the said light reflection film 10 is demonstrated.

  First, a transparent alignment substrate 4 is prepared. As the alignment substrate 4, for example, a glass substrate on which a rubbing-treated alignment film is formed is used.

  Next, a cholesteric liquid crystal constituting the cholesteric liquid crystal layer 1 is mixed with a solvent to prepare a liquid crystal solution having a predetermined concentration, and this liquid crystal solution is applied onto the alignment film of the alignment substrate 4. Thereby, the cholesteric liquid crystal is aligned. At this time, if necessary, alignment of the cholesteric liquid crystal is formed by heat treatment or the like. In the heat treatment, the liquid crystal is aligned by the self-alignment ability inherent in the liquid crystal substance by heating to the liquid crystal phase expression temperature range. As conditions for the heat treatment, optimum conditions and limit values differ depending on the liquid crystal phase behavior temperature (transition temperature) of the liquid crystal substance used, but it cannot be generally stated, but is usually in the range of 10 to 300 ° C, preferably 30 to 250 ° C. . If the temperature is too low, the alignment of the liquid crystal may not proceed sufficiently, and if the temperature is high, the liquid crystal substance may decompose or adversely affect the alignment substrate. Moreover, about heat processing time, it is 3 seconds-60 minutes normally, Preferably it is the range of 10 seconds-30 minutes. When the heat treatment time is shorter than 3 seconds, the alignment of the liquid crystal may not be sufficiently completed, and when the heat treatment time exceeds 60 minutes, the productivity is extremely deteriorated.

  The solvent constituting the liquid crystal solution varies depending on the type of cholesteric liquid crystal to be used, but usually hydrocarbons such as toluene, xylene, butylbenzene, tetrahydronaphthalene, decahydronaphthalene, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, propylene glycol dimethyl ether, tetrahydrofuran Ethers such as methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, etc., ethyl acetate, butyl acetate, ethylene glycol monomethyl ether acetate, propylene glycol monomethyl ether acetate, ethyl lactate, esters such as γ-butyrolactone, N-methyl- Amides such as 2-pyrrolidone, dimethylformamide, dimethylacetamide, dichloromethane, Carbon, tetrachloroethane, halogenated hydrocarbon such as chlorobenzene, butyl alcohol, triethylene glycol, diacetone alcohol, alcohol such as hexylene glycol. These solvents may be appropriately mixed and used as necessary. The concentration of the solution varies depending on the molecular weight and solubility of the cholesteric liquid crystal used, and finally the thickness of the target cholesteric liquid crystal layer 1, but cannot be determined unconditionally, but is usually 1 to 60% by mass, preferably 3 to 40% by mass.

  In addition, a surfactant may be added to the liquid crystal solution to facilitate coating. Examples of the surfactant include cationic systems such as imidazoline, quaternary ammonium salts, alkylamine oxides, and polyamine derivatives. Surfactant, polyoxyethylene-polyoxypropylene condensate, primary or secondary alcohol ethoxylate, alkylphenol ethoxylate, polyethylene glycol and its ester, sodium lauryl sulfate, ammonium lauryl sulfate, lauryl sulfate amines, alkyl-substituted fragrance Anionic surfactants such as aromatic sulfonates, alkyl phosphates, aliphatic or aromatic sulfonic acid formalin condensates, amphoteric surfactants such as laurylamidopropylbetaine, laurylaminoacetic acid betaine, polyethylene glycol Fatty acid esters, nonionic surfactants such as polyoxyethylene alkylamine, perfluoroalkyl sulfonate, perfluoroalkyl carboxylate, perfluoroalkyl ethylene oxide adduct, perfluoroalkyl trimethyl ammonium salt, perfluoroalkyl group And an oligomer containing a hydrophilic group, an oligomer containing a perfluoroalkyl and a lipophilic group, a fluorosurfactant such as a perfluoroalkyl group-containing urethane, and the like.

  The addition amount of the surfactant depends on the kind of the surfactant, the solvent, or the alignment film of the alignment substrate 4 to be applied, but is usually 10 ppm to 10%, preferably 50 ppm to 5 as a ratio to the mass of the cholesteric liquid crystal. %, More preferably in the range of 0.01% to 1%.

  Moreover, in order to improve the heat resistance of the cholesteric liquid crystal layer 1 and the like, a cross-linking agent such as a bisazide compound or glycidyl methacrylate is added to the liquid crystal solution so as not to disturb the expression of the cholesteric liquid crystal phase. You can also In addition, a polymerizable functional group having a basic skeleton such as a biphenyl derivative, a phenylbenzoate derivative, or a stilbene derivative into which a functional group such as an acryloyl group, a vinyl group, or an epoxy group has been introduced is introduced into a liquid crystal material in advance to develop a cholesteric phase and crosslink You may let them.

  The application method of the liquid crystal solution is not particularly limited as long as the uniformity of the coating film is ensured, and a known method can be adopted. Examples thereof include a roll coating method, a die coating method, a dip coating method, a curtain coating method, and a spin coating method. After the application, a solvent removal (drying) step by a method such as a heater or hot air blowing may be added. The thickness of the applied film in a dry state is set to be larger than 0.3 μm, for example. When the film thickness is 0.3 μm or less, the number of reflection peaks is 2 or less even when white light is incident, and the film is colored. Further, the pitch number of the liquid crystal in the applied film is set to 2 or less. When the pitch number of the spiral of the liquid crystal exceeds 2, it is colored even when white light is incident.

  At this time, the film thickness is controlled, for example, by adjusting the coating amount of the liquid crystal solution so as to be larger than 0.3 μm after the liquid crystal solution is dried, and the pitch number of the spiral is determined based on the amount and orientation of the chiral dopant added to the cholesteric liquid crystal. Therefore, the temperature of the heat treatment is adjusted to 2 or less by adjusting the temperature.

  After the cholesteric liquid crystal alignment is formed, the alignment is fixed. In this case, after the alignment of the cholesteric liquid crystal is completed by heat treatment or the like, the cholesteric liquid crystal on the alignment substrate 4 is fixed as it is by using means suitable for the liquid crystal used. Examples of such means include glass fixation by rapid cooling, and crosslinking by irradiation with energy such as heat, ultraviolet rays, and electron beams.

  Next, an isotropic layer 3 which is an alignment film similar to the above is formed on the cholesteric liquid crystal layer 1 by, for example, a spin coating method, and the isotropic layer 3 is subjected to a rubbing process. Here, the isotropic layer 3 also plays a role of preventing the solvent in the liquid crystal solution from dissolving the cholesteric liquid crystal in the cholesteric liquid crystal layer 1. At this time, the isotropic layer 3 is preferably composed of polyvinyl alcohol (PVA). The reason is as follows. That is, since PVA is soluble in an aqueous solvent, even if the cholesteric liquid crystal in the cholesteric liquid crystal layer 1 is composed of a polymer liquid crystal material, the PVA is not dissolved on the cholesteric liquid crystal layer 1 without dissolving the cholesteric liquid crystal layer 1. It is possible to form the layer as an alignment film. Further, when the cholesteric liquid crystal layer 2 is formed, the formed PVA layer becomes a barrier layer against a solvent that dissolves the cholesteric liquid crystal layer 1, and can be further rubbed and functions as an alignment film. Further, when the alignment film is polyimide, heat treatment at a high temperature close to 300 degrees with respect to the polyimide precursor is necessary in order to obtain a dense film as a barrier layer. At this temperature, the cholesteric liquid crystal layer 1 becomes isotropic from the liquid crystal phase, and the alignment state is disturbed, so that the uniform cholesteric liquid crystal layer 1 cannot be maintained. On the other hand, in the case of PVA, a dense barrier layer can be formed without performing such heat treatment at a high temperature, and a uniform cholesteric liquid crystal layer 1 can be maintained. Here, “densely dense” means a bulky and high density state. In addition, polyimide is colored yellow because it absorbs on the short wavelength side, whereas PVA is almost completely transparent.

  Next, the cholesteric liquid crystal layer 2 is formed on the isotropic layer 3 in the same manner as described above.

  When the cholesteric liquid crystal layer 2 is prepared in advance, the isotropic layer 3 may be directly bonded to the cholesteric liquid crystal layer 2 by heat fusion or the like. In this way, the light reflection film 10 is obtained.

  According to the manufacturing method, it is not necessary to prepare a plurality of cholesteric liquid crystals having different helical pitches as the cholesteric liquid crystals of the cholesteric liquid crystal layers 1 and 2. For this reason, it is not necessary to add a chiral dopant having a strong twisting power to the cholesteric liquid crystal to narrow the helical pitch in the cholesteric liquid crystal layer in order to form a selective reflection wavelength band to the short wavelength side, making it possible to produce a light reflecting film. It becomes easy.

(Simulation results of reflection spectrum and xy color coordinates when the thickness of the PVA layer in the light reflection film is changed)
For a light reflective film having an ABABA structure (A: cholesteric liquid crystal layer composed of left-handed twisted polymer cholesteric liquid crystal, B: PVA layer), the reflection spectrum and xy color coordinates when the film thickness of the PVA layer is changed A simulation was performed. The simulation was calculated by the 4 × 4 matrix method under the following conditions. The simulation was performed assuming that left circularly polarized light was vertically incident on the light reflecting film.
-Thickness of each cholesteric liquid crystal layer: 3.18 nm
-Number of spiral pitches in cholesteric liquid crystal: 1
Cholesteric liquid crystal ne: 1.78
・ No of cholesteric liquid crystal: 1.56
-Center wavelength of selective reflection band for cholesteric liquid crystal: 530 nm
-Refractive index n of the PVA layer: 1.50

The simulation result of the xy color coordinate values is shown in Table 1, and the simulation result of the reflection spectrum is shown in FIG. In Table 1 and FIG. 2, a <b> 1-h <b> 1 indicates a symbol for distinguishing the light reflecting film.

  As shown in FIG. 2 and Table 1, when the thickness of the PVA layer was 0.3 μm or less, only two sharp and large peaks appeared in the reflection spectrum. Further, the xy color coordinate values did not correspond to the white color referred to in this specification.

  On the other hand, when the thickness of the PVA layer was larger than 0.3 μm, three or more sharp and large peaks appeared in the reflection spectrum. Further, the xy color coordinate value corresponds to white as used in this specification.

  Therefore, it was confirmed from the simulation results that when the thickness of the PVA layer is larger than 0.3 μm, the white light can be reflected with sufficient intensity when the white light is incident.

(Simulation results of reflection spectrum and xy color coordinates when the number of spiral pitches of cholesteric liquid crystal in the light reflection film is changed)
For a light reflective film having an ABABA structure (A: cholesteric liquid crystal layer composed of left-handed twisted polymer cholesteric liquid crystal, B: PVA layer), the reflection spectrum when the number of helical pitches in the cholesteric liquid crystal of the cholesteric liquid crystal layer is changed and A simulation of xy color coordinates was performed. The simulation was performed as described above under the following conditions. The simulation was performed assuming that left circularly polarized light was vertically incident on the light reflecting film.
Cholesteric liquid crystal ne: 1.78
・ No of cholesteric liquid crystal: 1.56
-Center wavelength of selective reflection band for cholesteric liquid crystal: 530 nm
-Refractive index n of the PVA layer: 1.50
-PVA layer thickness: 0.5 μm

The simulation result of the xy color coordinate values is shown in Table 2, and the simulation result of the reflection spectrum is shown in FIG. In Table 2 and FIG. 3, a2-e2 represents a symbol for distinguishing the light reflecting film.

  As shown in FIG. 3 and Table 2, when the pitch number of the cholesteric liquid crystal layer exceeded 3, sharp and large reflection spectra approached each other. And the xy color coordinate value corresponded to the white said by this specification.

  On the other hand, when the pitch number of the cholesteric liquid crystal layer is 2 or less, sharp and large peaks are separated from each other in the reflection spectrum. And the xy color coordinate value corresponded to the white said by this specification.

  From the above, it was confirmed that the configuration of the light reflecting film of the present invention was able to achieve the reflection of white light, which is the object of the present invention, although it was a result of simulation.

  The present invention is not limited to the above embodiment. For example, in the above embodiment, the number of cholesteric liquid crystal layers is two, but the number of cholesteric liquid crystal layers may be plural, and may be three or more. In this case, it is necessary to provide the isotropic layer 3 between adjacent cholesteric liquid crystal layers. Further, in the above embodiment, the cholesteric liquid crystal spirals in the cholesteric liquid crystal layers 1 and 2 are on the left, but if the cholesteric liquid crystal layers have the same spiral hand, they are on the right. Also good.

(Laser oscillation element)
Next, an embodiment of the laser oscillation element of the present invention will be described with reference to FIG. FIG. 5 is a side view showing a preferred embodiment of the laser oscillation element according to the present invention. In addition, the same code | symbol is attached | subjected to the same or equivalent component as embodiment of the invention which concerns on the said light reflection film, and the overlapping description is abbreviate | omitted.

  As shown in FIG. 5, the laser oscillation element 100 according to the present embodiment includes a first light reflection film 101 and a second light reflection film 102 that are arranged to face each other, and the first light reflection film 101. An anisotropic medium layer 103 including an anisotropic medium is provided between the first light reflecting film 102 and the second light reflecting film 102. The anisotropic medium layer 103 further contains a dye that emits fluorescence upon photoexcitation. Here, the emission band of the fluorescence emitted from the dye is in the wavelength region of visible light. Moreover, both the 1st light reflection film 101 and the 2nd light reflection film 102 are comprised with the light reflection film 10 mentioned above. In the present embodiment, the first light reflecting film 101 and the second light reflecting film 102 are provided so as to be plane-symmetric with respect to the anisotropic medium layer 103. That is, in the first light reflecting film 101 and the second light reflecting film 102, the cholesteric liquid crystal layer 2, the isotropic layer 3, the cholesteric liquid crystal layer 1 and the alignment substrate 4 are sequentially arranged from the defect layer 103 side. Therefore, the peak in the reflection spectrum of the first light reflection film 101 and the peak in the second reflection spectrum 102 overlap in the wavelength region of visible light.

  According to the laser oscillation element 100 of the present embodiment, the light reflecting film 10 capable of reflecting white light with sufficient intensity even if thin is used as the first light reflecting film 101 and the second light reflecting film 102. ing. Thus, when the laser oscillation element 100 is irradiated with light that excites the dye, three or more oscillation peaks can be observed in the wavelength region of visible light. For this reason, by using a filter that selectively cuts a specific wavelength, it is possible to extract light of an arbitrary wavelength from among a plurality of wavelengths corresponding to three or more oscillation peaks even though it is a single laser oscillation element. And the range of selection for the wavelength of the light to be extracted can be expanded. According to the laser oscillation device 100, white light can be laser-oscillated when three or more oscillation peaks are distributed in the vicinity of each of the blue wavelength, the green wavelength, and the red wavelength.

  Further, according to the laser oscillation element 100, the number of oscillation peaks can be adjusted by adjusting the irradiation energy of the light that excites the dye, and thereby the oscillation wavelength can be controlled. Specifically, the number of appearing oscillation peaks can be increased by increasing the irradiation energy of light. In this case, since it is not necessary to use a filter as described above, a wavelength tunable laser oscillation element can be realized with a simple optical system.

  Furthermore, even if the first light reflecting film 101 and the second light reflecting film 102 are thin, sufficient white light can be reflected. Therefore, the first light reflecting film 101 and the second light reflecting film 102 can be made thin, and as a result, laser The size of the oscillation element 100 can be reduced.

  In the anisotropic medium layer 103, the anisotropic medium only needs to contain an anisotropic medium. For example, the anisotropic medium is composed of a low-molecular nematic liquid crystal, a polymer nematic liquid crystal, or the like.

（上記式中、Ｒ^１がＯ（ＣＨ_２）_１２Ｈである場合は、Ｒ^２はＨ又はｔ−Ｂｕを表し、Ｒ^１がＣＨ_２ＣＨ（ＣＨ_２ＣＨ_３）ＣＨ_２ＣＨ_２ＣＨ_２ＣＨ_３である場合は、Ｒ^２は水素又はｔ−Ｂｕを表し、ｍは１以上の整数を表す。）
で表される化合物、又は下記構造式：

（上記式中、Ｒ^３がＣＨ_２ＣＨ（ＣＨ_２ＣＨ_３）ＣＨ_２ＣＨ_２ＣＨ_２ＣＨ_３である場合は、Ｒ^４はＨ又はｔ−Ｂｕを表し、ｎは１以上の整数を表す。）
で表される化合物なども用いることができる。これらの化合物の分子量は特に規定されないが、５万以下であることが好ましい。分子量が５万以上の場合は粘性が高くなり配向性が悪化するため好ましくない。 Here, the dye may be anything as long as it can emit light by photoexcitation, and may be either an organic dye or an inorganic dye. Here, the light emitted by photoexcitation includes not only fluorescence but also phosphorescence. Examples of organic dyes include styryl, xanthene, oxazine, coumarine, stilben derivatives, oxazole derivatives, oxadiazole derivatives, p- Examples thereof include an oligophenylene derivative and a 4H-pyranylidenepropanedinitrile derivative (DCM). In addition, the following chemical structural formula:

(In the above formula, when R ¹ is O (CH ₂ ) ₁₂ H, R ² represents H or t-Bu, and R ¹ is CH ₂ CH (CH ₂ CH ₃ ) CH ₂ CH ₂ CH ₂ CH. _In the case of ₃ , R ² represents hydrogen or t-Bu, and m represents an integer of 1 or more.)
Or a compound represented by the following structural formula:

(In the above formula, when R ³ is CH ₂ CH (CH ₂ CH ₃ ) CH ₂ CH ₂ CH ₂ CH ₃ , R ⁴ represents H or t-Bu, and n represents an integer of 1 or more. )
A compound represented by the formula can also be used. The molecular weight of these compounds is not particularly limited, but is preferably 50,000 or less. A molecular weight of 50,000 or more is not preferable because the viscosity increases and the orientation deteriorates.

で表されるクォーターチオフェン（ＱＴ：Quarter Thiophene）も使用することができる。 Further, as the organic dye, the following structural formula:

The quarter thiophene (QT: Quarter Thiophene) represented by these can also be used.

Examples of inorganic dyes include zinc sulfide, zinc silicate, zinc cadmium sulfide, calcium sulfide, strontium sulfide, calcium tungstate, canary glass, platinum cyanide, sulfides of alkaline earth metals, rare earth compounds, and the like.
Of the above dyes, organic dyes are particularly preferable. In this case, there is an advantage that the solubility in the liquid crystal is excellent and the alignment of the liquid crystal is hardly hindered.

  In the above embodiment, the dye is described as being included in the anisotropic medium layer 103, but the dye is not necessarily included in the anisotropic medium 103. For example, the first light reflecting film 101 or It may be included in the second light reflecting film 102. In this case, the dye may be contained in, for example, the cholesteric liquid crystal layer 1 or 2 or the isotropic layer 103 in the first light reflecting film 10 and the second light reflecting film 20.

  Moreover, in the said embodiment, although the 1st light reflection film 101 and the 2nd light reflection film 102 were comprised with the light reflection film 10, the 1st light reflection film 101 and the 2nd light reflection film 102 are not necessarily the same structure. It is not necessary to have a different configuration. However, in the first light reflection film 101 and the second light reflection film 102, the peak in the reflection spectrum of the first light reflection film 101 and the peak in the second reflection spectrum 102 need to overlap in the wavelength region of visible light. There is.

  Further, the cholesteric liquid crystal used in the first light reflecting film 101 and the cholesteric liquid crystal used in the second light reflecting film 102 may have the same or different spiral hand, but may be the same. preferable.

  In addition, the first light reflecting film 101 and the second light reflecting film 102 may have the same or different spiral pitch numbers of cholesteric liquid crystal, but the same is preferable because laser oscillation is more likely to occur.

  The isotropic layer in the first light reflecting film 101 and the isotropic layer in the second light reflecting film 102 need only have a thickness greater than 0.3 μm, and are not necessarily the same.

  Next, the content of the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples.

Example 1
First, a polymer cholesteric liquid crystal solution for forming a cholesteric liquid crystal layer (hereinafter referred to as a “PCLC film”) 1 having a left-handedness, that is, an L structure was prepared as follows. That is, a liquid crystal mixture of polymer achiral nematic liquid crystal composed of aromatic polyester and polymer chiral nematic liquid crystal composed of aromatic polyester (LC film manufactured by Nippon Oil Corporation) was dissolved in chloroform. A polymer cholesteric liquid crystal solution was obtained. Here, the mixing ratio of the polymer chiral nematic liquid crystal in the liquid crystal mixture was set to 87% by mass for the left-handed polymer chiral nematic liquid crystal and 13% by mass for the polymer achiral nematic liquid crystal. The concentration of the liquid crystal mixture in the polymer cholesteric liquid crystal solution was 10% by mass.

によって算出したものである。 This polymer cholesteric liquid crystal solution was spin-coated on a glass substrate having a polyimide alignment film (1254 manufactured by JSR Corporation) rubbed in one direction at a rotation speed of 4000 rpm and a rotation time of 1 minute, and then applied to the cholesteric liquid crystal solution. It was heated to 180 ° C. and cured for 2 minutes. Thus, a well-oriented polymer cholesteric liquid crystal film 1 having a thickness of 0.484 μm (= 484 nm) was formed on the polyimide alignment film on the glass substrate. That is, the PCLC film 1 was obtained on the alignment substrate 4. At this time, the helical axis of the PCLC film 1 was perpendicular to the surface of the glass substrate. Moreover, the transmission spectrum was measured about the PCLC film 1, and the short wavelength end and the long wavelength end were computed in the selective reflection wavelength band. And the center wavelength of the selective reflection of the PCLC film 1 was determined by the arithmetic average. As a result, the center wavelength of selective reflection was 532 nm. The pitch number of the spiral of the PCLC film 1 was 484 nm / (532 / 1.67) nm = 1.52. Here, ne and no of the cholesteric liquid crystal are 1.78 and 1.56, respectively, and the above “1.67” is represented by the following formula:

It is calculated by.

  Next, the PVA solution was spin-coated on the PCLC film 1, dried, and then heated at 100 ° C. for 30 minutes to obtain a PVA film having a thickness of 0.35 μm. The PVA solution was obtained by dissolving PVA in purified water as a solvent. At this time, the PVA concentration in the PVA solution was set to 3% by mass. Thereafter, the PVA film was rubbed in a certain direction.

  On the other hand, in order to form the PCLC film 2, a polymer cholesteric liquid crystal solution was prepared in the same manner as described above. Then, using this polymer cholesteric liquid crystal solution, a well-oriented PCLC film 2 having a thickness of about 0.484 μm was formed on the PVA film in the same manner as described above. At this time, the helical axis of the PCLC film 2 was perpendicular to the surface of the glass substrate.

  Moreover, the transmission spectrum was measured about the laminated body of the cholesteric liquid crystal layer 1 and the cholesteric liquid crystal layer 2, and the short wavelength end and the long wavelength end were calculated in the selective reflection wavelength band. And the center wavelength of the selective reflection of the laminated body of the cholesteric liquid crystal layer 1 and the cholesteric liquid crystal layer 2 was determined by the arithmetic average. As a result, the center wavelength of selective reflection was 532 nm. Since the PCLC film is formed of the same material, the PCLC film 2 has the same spiral pitch as the PCLC film 1, and the number of pitches is 484 nm / (532 nm / 1.67) = 1.52 pitch. I understood that.

  Similarly, a PVA film that is an isotropic layer, a PCLC film, a PVA film that is an isotropic layer, and a PCLC film were sequentially formed on the PCLC film 2.

  A light reflecting film was obtained as described above. The thickness of the portion of the light reflection film excluding the alignment substrate was 0.484 × 4 + 0.35 × 3 = 2.98 μm.

(Example 2)
The number of PCLC films is three, and an isotropic layer made of PVA is sandwiched between adjacent PCLC films, the number of spiral pitches of cholesteric liquid crystal is 2.0, and the thickness of the isotropic layer made of PVA is 0. A light reflecting film was produced in the same manner as in Example 1 except that the thickness was 50 μm. The thickness of the produced light reflecting film excluding the alignment substrate was 2.0 × (0.532 / 1.67) × 3 + 0.50 × 2 = 2.91 μm.

(Comparative Example 1)
The number of PCLC films is three, the isotropic layer of PVA made of PVA is sandwiched between adjacent PCLC films, the pitch number of the spiral of the PCLC film is 5.0, and the center of the selective reflection band A light reflecting film was produced in the same manner as in Example 1 except that the wavelength was 540 nm. The thickness of the produced light reflection film excluding the alignment substrate was 5.0 × (0.540 / 1.67) × 3 + 0.52 × 2 = 5.89 μm.

(Comparative Example 2)
Implemented except that PCLC film 1 and an isotropic layer with a thickness of 0.52 μm were formed on alignment substrate 4, the helical pitch number of PCLC film 1 was 5.0, and the central wavelength of the selective reflection band was 540 nm. A light reflecting film was produced in the same manner as in Example 1. The thickness of the produced light reflection film excluding the alignment substrate was 5.0 × (0.540 / 1.67) = 1.62 μm.

(Measurement of reflection spectrum and xy color coordinates)
The reflection spectrum was measured about the light reflection film obtained in Examples 1-2 and Comparative Examples 1-2. The results are shown in FIG. The reflection spectrum was measured using a microscope spectrum meter (ORC TFM-120AFT-PC). Moreover, about the light reflection film obtained in Examples 1-2 and Comparative Examples 1-2, the xy color coordinate was calculated | required from the reflection spectrum. The results are shown in Table 3. Regarding “layer configuration” in Table 3, “A” indicates a cholesteric liquid crystal layer, and “B” indicates an isotropic layer. HX means that the number of cholesteric liquid crystal layers is X.

  From the results shown in FIG. 4, in the light reflecting films of Examples 1 and 2, the sharp reflection peak centered around the blue wavelength, the sharp reflection peak centered around the green wavelength, and the sharp centered around the red wavelength. A reflection peak was confirmed. Moreover, when white light was actually incident on the light reflecting film of Examples 1 and 2 in the thickness direction of the light reflecting film using a white light source (white LED light), the light reflecting film appeared white. It was. Furthermore, the xy color coordinates also corresponded to the white color referred to in this specification.

  On the other hand, in the light reflection films of Comparative Examples 1 and 2, a plurality of sharp reflection peaks were not confirmed. Moreover, when white light was actually made to enter also with respect to the light reflection film of Comparative Examples 1-2 like Example 1-2, it was confirmed that a light reflection film shows green. Further, the xy color coordinates deviated from the white color referred to in this specification.

  In addition, when the reflection spectrum of the light reflection film of Example 2 and the simulation result of the reflection spectrum of the light reflection film of “b2” in FIG. 3 are compared, the results are almost similar, and the xy color coordinates are mutually similar. It was close. Moreover, when the reflection spectrum of the light reflection film of Comparative Example 1 and the simulation result of the reflection spectrum of the light reflection film “e2” in FIG. 3 are compared, the results are almost similar, and the xy color coordinates Were also close to each other. Therefore, there is no significant difference between the simulation results and the results of the examples and comparative examples, and the reliability of the simulation results is considered to be sufficiently high.

  From the above, it was confirmed that the light reflecting film of the present invention can reflect white light with sufficient intensity even if it is thin.

(Example 3)
Next, production of a laser oscillation element was tried using the light reflecting film (cholesteric / PVA multilayer film) M1 obtained in Example 1. That is, two light reflecting films M1 having four layers of PCLC films and three layers of PVA films sandwiched between adjacent PCLC films were prepared. In the light reflection film M1, the PCLC layers located farthest from the glass substrate were stacked so as to face each other through spacer beads having a diameter of 2 μm.

  Next, a low molecular nematic liquid crystal containing a laser oscillation dye was prepared as follows. That is, first, 0.49 parts by weight and 0.15 parts by weight of Coumarin 153 (Lambda Physik) and DCM (manufactured by Exciton) as laser dyes are added to 100 parts by weight of a low molecular nematic liquid crystal (ZLI-2293) manufactured by Merck. The mixture was mixed to a concentration of The chemical structural formulas of these laser dyes are as shown in FIG. The laser dye-containing low-molecular nematic liquid crystal obtained in this way is heated to 88 ° C. and is in an isotropic phase, and is injected into the gap of 2 μm thickness formed by overlapping the light reflecting films M1 by utilizing capillary action. A multilayer film (laser oscillation element) M2 was obtained.

  Next, the multilayer film M2 was irradiated with a pulse laser beam having a wavelength of 420 nm obtained by making the third harmonic of the Nd: YAG laser incident on an optical parametric oscillator (OPO), and was optically excited.

  When the irradiation energy was 21.5 μJ / pulse, as shown in FIG. 7, a laser oscillation having one peak at 508 nm was generated from the multilayer film M2. At this time, the color of the emission spectrum was yellow green of (0.35, 0.54) on the CIE color coordinates, and the peak wavelength was dark green of (0.04, 0.79).

  When the irradiation energy was increased to 31.1 μJ / pulse, laser oscillation having two peaks at 508 nm and 488 nm occurred as shown in FIG. The color of the emission spectrum is yellowish green of (0.30, 0.55) on the CIE color coordinates, and the two peak wavelengths are (0.05, 0.0.28) and (0.05, 0. 82).

  When the irradiation energy was further increased to 49.9 μJ / pulse, laser oscillation having three peaks at 508 nm, 488 nm, and 595 nm occurred as shown in FIG. At this time, the color of the emission spectrum is green of (0.29, 0.51) on the CIE color coordinates, and the three peak wavelengths are (0.05, 0.26) and (0.02, 0. 75) and (0.61, 0.39). 7 to 9 show the relationship between the oscillation peak and the color coordinates in the oscillation spectrum graph.

  As described above, it was found that a laser oscillation element can be easily obtained by using the light reflecting film according to the present invention, and that the emission peak of the laser beam can be adjusted by adjusting the excitation energy. Furthermore, it was confirmed that three oscillation peaks were observed in the wavelength region of visible light by lowering the irradiation energy. From this, it was also found that if a filter that selectively reflects wavelengths is used, light of three types of wavelengths can be extracted.

It is a side view which shows one Embodiment of the light reflection film which concerns on this invention. It is a graph which shows the simulation result of a reflection spectrum when changing the film thickness of the PVA layer in a light reflection film. It is a graph which shows the simulation result of a reflection spectrum when changing the helical pitch number in the cholesteric liquid crystal of the cholesteric liquid crystal layer in a light reflection film. It is a graph which shows the measurement result of the reflection spectrum which concerns on the light reflection film of Examples 1-2 and Comparative Examples 1-2. It is a side view which shows one Embodiment of the laser oscillation element of this invention. FIG. 4 is a diagram showing a chemical structural formula of a laser dye used in Example 3. 6 is a graph showing a laser oscillation spectrum when the laser oscillation element according to Example 3 is irradiated with excitation light having an irradiation energy of 21.5 μJ / Pulse. 6 is a graph showing a laser oscillation spectrum when the laser oscillation element according to Example 3 is irradiated with excitation light having an irradiation energy of 31.1 μJ / Pulse. 7 is a graph showing a laser oscillation spectrum when the laser oscillation element according to Example 3 is irradiated with excitation light having an irradiation energy of 49.9 μJ / Pulse.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 2 ... Cholesteric liquid crystal layer, 3 ... Isotropic layer, 10 ... Light reflection film, 100 ... Laser oscillation element, 101 ... 1st light reflection film, 102 ... 2nd light reflection film, 103 ... An anisotropic medium layer.

Claims (3)

A plurality of cholesteric liquid crystal layers including cholesteric liquid crystals;
An isotropic layer provided between the cholesteric liquid crystal layers adjacent to each other and made of an isotropic medium;
The cholesteric liquid crystal layer has a plurality of cholesteric liquid crystal layers having a spiral pitch number of 2 or less, and the spiral nature of the spirals is the same,
The spiral pitch of the cholesteric liquid crystal in the plurality of cholesteric liquid crystal layers is the same,
The central wavelength of the selective reflection band of the cholesteric liquid crystal is 500 to 560 nm,
A light reflecting film, wherein the thickness of the isotropic layer is greater than 0.3 μm.   The light reflecting film according to claim 1, wherein the isotropic medium is polyvinyl alcohol. First and second light reflecting films arranged opposite to each other;
An anisotropic medium layer provided between the first light reflecting film and the second light reflecting film and containing an anisotropic medium;
The first and second light reflecting films are the light reflecting films according to claim 1 or 2,
At least one of the first light reflecting film, the anisotropic medium layer, and the second light reflecting film contains a dye that emits fluorescence by photoexcitation,
The peak in the reflection spectrum of the first light reflection film and the peak in the second reflection spectrum overlap in the wavelength region of visible light,
A laser oscillation element in which an emission band of fluorescence emitted from the dye is in a wavelength region of visible light.

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