JP4102762B2 - Laser oscillation element - Google Patents

Description

  The present invention relates to a laser oscillation element using a cholesteric liquid crystal.

  Cholesteric liquid crystals have the property of selectively reflecting light of a specific wavelength, and in particular, selectively reflect circularly polarized light in the same rotational direction as the spiral winding of cholesteric liquid crystal and transmit reversely polarized circularly polarized light. Let

  With respect to such cholesteric liquid crystal, it has been reported that laser oscillation occurs at the edge portion of the selective reflection wavelength band (see, for example, Non-Patent Document 1).

Recently, there has been a proposal that laser oscillation should occur at a wavelength inside the selective reflection wavelength band in order to lower the threshold of laser oscillation, so a laser oscillation element that causes such laser oscillation. Various studies have been conducted on. As such a laser oscillation element, for example, an element in which two cholesteric liquid crystal films containing a pigment are superposed with their azimuth angles shifted is known (see, for example, Non-Patent Document 2).
Kopp, 4 others, “Low-threshold lasing at the edge of a photonic stop band in cholesteric liquid crystals”, Optics Letter USA, 1998, Vol. 23, p. 1707-1709 Ozaki, et al., “Defect modes and laser oscillation in the stop band of cholesteric liquid crystals”, Electrical Materials Technical Magazine, 2002, Vol. 11, No. 2, p. 165-167

  However, although the laser oscillation element described in Non-Patent Document 2 described above can cause laser oscillation at a wavelength within the selective reflection band, the thickness of the laser oscillation element is required to obtain a certain laser beam intensity. Needed to be large enough. That is, in the conventional laser oscillation element, laser oscillation could not be caused with high efficiency.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a laser oscillation element capable of causing laser oscillation with high efficiency.

  As a result of intensive studies to solve the above problems, the present inventors have found that the above problems can be solved by orienting the transition moment of the dye in the defect layer parallel to the surface of the cholesteric liquid crystal layer. The present invention has been completed.

That is, the laser oscillation device of the present invention includes a first cholesteric liquid crystal layer including cholesteric liquid crystal, a second cholesteric liquid crystal layer disposed opposite to the first cholesteric liquid crystal layer and including cholesteric liquid crystal, the first cholesteric liquid crystal layer, and the A defect layer including a dye that emits fluorescence by photoexcitation and is provided between the second cholesteric liquid crystal layer, and the selective reflection wavelength band in the cholesteric liquid crystal and the emission band of the fluorescence emitted from the dye are at least one. The cholesteric liquid crystals included in the first cholesteric liquid crystal layer and the second cholesteric liquid crystal layer have the same spiral winding direction, and the transition moment of the dye is the first cholesteric liquid crystal layer and For the surface of the second cholesteric liquid crystal layer Are oriented in parallel, the first cholesteric liquid crystal layer and said second cholesteric liquid crystal layer, a cholesteric liquid crystal director in the surface of the defect layer side of said first cholesteric liquid crystal layer, said second cholesteric liquid crystal layer The director of the cholesteric liquid crystal on the surface of the defect layer is arranged so as to be parallel to each other .

  When laser oscillation is caused in this laser oscillation element, light having a wavelength shorter than the selective reflection wavelength band in the first and second cholesteric liquid crystal layers is used as excitation light for the dye. According to the laser oscillation element of the present invention, the excitation light of the dye is incident on the first cholesteric liquid crystal layer, for example. Then, the excitation light is transmitted through the first cholesteric liquid crystal layer and incident on the defect layer, and the dye is excited to cause fluorescence emission, thereby causing laser oscillation. At this time, the laser oscillation element can cause laser oscillation with high efficiency. It is also possible to cause continuous laser oscillation.

  Here, the laser oscillation occurs with high efficiency in the defect layer, and the dye transition moment is aligned parallel to the surfaces of the first cholesteric liquid crystal layer and the second cholesteric liquid crystal layer. It is considered that the fluorescence extraction efficiency is sufficiently high.

  In the present invention, the orientation direction and orientation degree of the transition moment can be known, for example, by measuring the azimuth angle dependency of the absorbance with respect to linearly polarized light rotating in the azimuth angle direction.

  According to the laser oscillation device of the present invention, in the defect layer, the transition moment of the dye is aligned in parallel to the surfaces of the first cholesteric liquid crystal layer and the second cholesteric liquid crystal layer, thereby causing laser oscillation with high efficiency. It becomes possible to make it. It is also possible to cause continuous laser oscillation.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

(Laser oscillation element)
FIG. 1 is a cross-sectional view schematically showing an embodiment of a laser oscillation device of the present invention. As shown in FIG. 1, the laser oscillation element 1 includes a cholesteric liquid crystal layer (first cholesteric liquid crystal layer) 2 and a cholesteric liquid crystal layer (second cholesteric liquid crystal layer) 3, which are arranged to face each other. Has been. A defect layer 4 is provided between the cholesteric liquid crystal layers 2 and 3.

  A transparent alignment substrate 7 is provided on the opposite side of the defect layer 4 on the cholesteric liquid crystal layer 2, and a transparent alignment substrate 8 is provided on the opposite side of the defect layer 4 on the cholesteric liquid crystal layer 3. Yes.

  The defect layer 4 is made of an anisotropic medium. As the anisotropic medium, a medium containing the dye 5 and the nematic liquid crystal 6 is used. Here, the pigment | dye 5 is what can emit fluorescence by photoexcitation, and has anisotropy. Specific examples of the dye 5 will be described later.

  In the defect layer 4, the director of the nematic liquid crystal 6 and the transition moment of the dye 5 are aligned parallel to each other, and the transition moment of the dye 5 is aligned in a direction parallel to the surfaces of the cholesteric liquid crystal layers 2 and 3. ing.

  The cholesteric liquid crystal layer 2 includes cholesteric liquid crystal, and the cholesteric liquid crystal can selectively reflect light in a specific wavelength band due to a helical structure. As this cholesteric liquid crystal, a liquid crystal having a selective wavelength band overlapping with an emission band of fluorescence emitted from the dye 5 in at least a part of a wavelength region is used. Here, as a cholesteric liquid crystal, from the viewpoint of causing laser oscillation with sufficient light intensity, a liquid crystal that includes the wavelength at the emission peak of the fluorescence emission band within the selective reflection wavelength band is preferable. In this embodiment, the spiral direction of the cholesteric liquid crystal is left. That is, the spiral of the cholesteric liquid crystal is left-handed. A specific example of the cholesteric liquid crystal will be described later.

  The cholesteric liquid crystal layer 3 includes the same cholesteric liquid crystal as the cholesteric liquid crystal of the cholesteric liquid crystal layer 2. Therefore, in this embodiment, the spiral direction of the cholesteric liquid crystal of the cholesteric liquid crystal layer 3 is also on the left. Accordingly, the cholesteric liquid crystal layer 2 and the cholesteric liquid crystal layer 3 have the same winding direction of the cholesteric liquid crystal. Accordingly, when light is incident on the cholesteric liquid crystal layer 2 and the cholesteric liquid crystal layer 3, a part of the incident light is selectively reflected due to the periodic structure due to the spiral.

  Further, in the cholesteric liquid crystal layers 2 and 3, the director of the cholesteric liquid crystal on the surface of the cholesteric liquid crystal layer 2 on the defect layer 4 side and the director of the cholesteric liquid crystal on the surface of the cholesteric liquid crystal layer 3 on the defect layer 4 side are parallel to each other. Are arranged as follows. By doing so, the defect layer 4 functions as a discontinuous layer in the continuous spiral structure, and it is possible to cause laser oscillation within the selective reflection wavelength band of the cholesteric liquid crystal. In addition, when the nematic liquid crystal 6 exhibits a nematic liquid crystal phase state, the director of the nematic liquid crystal 6 can be maintained parallel to the surface of the cholesteric liquid crystal layer 2 or the cholesteric liquid crystal layer 3.

(Nematic liquid crystal)
The nematic liquid crystal 6 is not particularly limited as long as it can exhibit a nematic liquid crystal phase state, and may be either a polymer liquid crystal or a low molecular liquid crystal. As the polymer liquid crystal, various main chain type polymer liquid crystal substances, side chain type polymer liquid crystal substances, or 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.

  Examples of low-molecular liquid crystals 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, and 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 A composition to which an ionic compound is added is used.

(Dye)
The dye 5 is not particularly limited as long as it can emit fluorescence by photoexcitation and has transition moment anisotropy, and may be either an organic dye or an inorganic dye. Examples of organic dyes include styryl, xanthene, oxazine, coumarine, stilben derivatives, oxazole derivatives, oxadiazole derivatives, p- In addition to Origophenylene derivatives, Journal of Chemical Society, 2002, No. 124, p. And those represented by the chemical structural formula described in 9670 (in the case of R = EtH, R ′ = t-Bu). 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, the dye can be dissolved in a solvent, and in particular, by dissolving it in the liquid crystal, the transition moment is oriented in a certain direction, increasing the absorption efficiency for incident light from a specific direction, and obtaining high-efficiency fluorescent emission. There is an advantage that

(Cholesteric liquid crystal)
The cholesteric liquid crystal that constitutes the cholesteric liquid crystal layers 2 and 3 has a selective reflection wavelength band that overlaps at least a part of the wavelength band of the fluorescence emitted from the dye 5 and can fix the cholesteric alignment. At least.

  The liquid crystal substance includes a polymer liquid crystal substance and a low molecular liquid crystal substance, and various main chain type liquid crystal substances, side chain type polymer liquid crystal substances, or a mixture thereof is used as the polymer liquid crystal substance. Can do.

  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.

  Suitable examples of the structural unit of the polymer 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.

  As a method of forming the cholesteric liquid crystal layers 2 and 3, a known method can be used. The cholesteric liquid crystal layers 2 and 3 can be obtained by forming an alignment film on a transparent substrate, rubbing the alignment film, applying a liquid crystal material containing the cholesteric liquid crystal as an essential component, and performing a heat treatment. .

(Oriented substrate)
The alignment substrates 7 and 8 are not particularly limited as long as they are transparent to the excitation light and fluorescence of the dye 5 and can support the cholesteric liquid crystal layers 2 and 3. For example, polyimide, polyamide, polyamideimide, polyphenylene sulfide, polyphenylene oxide, polyether ketone, polyether ether ketone, polyether sulfone, polysulfone, polyethylene terephthalate, polyethylene naphthalate, polyarylate, triacetyl cellulose, epoxy resin, phenol resin Or a uniaxially stretched film of these films. Depending on the production method, these films may show sufficient alignment ability for the cholesteric liquid crystal used in the cholesteric liquid crystal layers 2 and 3 without performing treatment for expressing the alignment ability again. Is insufficient, or does not show orientation ability, etc., if necessary, these films may be stretched under moderate heating, or the film surface may be rubbed in one direction with a rayon cloth or the like, or the film may be rubbed. An alignment film made of a known alignment agent such as polyimide, polyvinyl alcohol, or a silane coupling agent is provided on the surface to perform a rubbing process, an oblique deposition process such as silicon oxide, or a combination of these processes as appropriate. Thus, a film exhibiting orientation ability may be used. Various glass plates provided with regular fine grooves on the surface can also be used as the alignment substrates 7 and 8.

  As the alignment substrates 7 and 8, those obtained by forming the rubbed polyimide films 11 and 12 on the transparent substrates 9 and 10 are preferably used.

(Laser oscillation device manufacturing method)
The laser oscillation element 1 can be manufactured as follows.

  First, transparent alignment substrates 7 and 8 are prepared. As the alignment substrates 7 and 8, for example, glass substrates on which a rubbing-treated alignment film is formed are used.

  Next, a cholesteric liquid crystal constituting the cholesteric liquid crystal layers 2 and 3 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 films of the alignment substrates 7 and 8. 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. Further, since the concentration of the solution varies depending on the molecular weight and solubility of the cholesteric liquid crystal to be used, and finally the thickness of the target cholesteric liquid crystal layers 2 and 3, etc., it cannot be determined unconditionally. Preferably it is 3 to 40 weight%.

  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 -Fluorosurfactants such as hydrophilic group-containing oligomers, perfluoroalkyl / lipophilic group-containing oligomers 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 substrates 7 and 8 to be applied, but is usually 10 ppm to 10%, preferably 50 ppm as a ratio to the weight of the cholesteric liquid crystal. -5%, more preferably 0.01% -1%.

  Further, in order to improve the heat resistance of the cholesteric liquid crystal layers 2 and 3, a crosslinking 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. Can also be crosslinked. 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 is introduced is introduced into a liquid crystal material in advance to express a cholesteric phase and to crosslink. You may let them.

  The application method 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 film thickness of the applied film in a dry state is usually 0.3 to 20 μm, preferably 0.5 to 10 μm, and more preferably 0.7 to 3 μm. Outside this range, the optical performance of the obtained cholesteric liquid crystal layers 2 and 3 is insufficient, and the orientation of the cholesteric liquid crystal becomes insufficient.

  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 substrates 7 and 8 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, the alignment substrates 7 and 8 are connected via a spacer (not shown) so that the cholesteric liquid crystal layers 2 and 3 face each other. At this time, the alignment substrates 7 and 8 are connected to each other so that the director of the cholesteric liquid crystal on the inner surface of the cholesteric liquid crystal layer 2 and the director of the cholesteric liquid crystal on the inner surface of the cholesteric liquid crystal layer 3 are parallel.

  Then, a solution in which nematic liquid crystal 6 and dye 5 are mixed in a solvent is prepared, and this solution is sealed in the space between the alignment substrates 7 and 8 by utilizing capillary action. Remove. Thereby, the defect layer 4 is obtained between the cholesteric liquid crystal layers 2 and 3. At this time, since the director of the cholesteric liquid crystal on the inner surface of the cholesteric liquid crystal layer 2 and the director of the cholesteric liquid crystal on the inner surface of the cholesteric liquid crystal layer 3 are parallel, the nematic liquid crystal 6 has a nematic liquid crystal phase state. The director is oriented in a direction parallel to the surfaces of the orientation substrates 7 and 8. The laser oscillation element 1 is obtained as described above.

  In the above manufacturing method, the cholesteric liquid crystal layers 2 and 3 are connected to each other through a spacer, the solution is sealed, and then the solvent is removed to align the nematic liquid crystal 6 so that the cholesteric liquid crystal layers 2 and 3 are aligned. In the case where the defect layer 4 is formed but the alignment of the dye 5 and the nematic liquid crystal 6 is fixed and the defect layer 4 is originally produced, that is, when the defect layer 4 is made of a polymer film, The cholesteric liquid crystal layer 2, the defect layer 4, and the cholesteric liquid crystal layer may be laminated with each other using an adhesive or the like.

(Operation of laser oscillation element)
Next, the operation of the laser oscillation element 1 will be described.

  In order to cause laser oscillation in the laser oscillation element 1, light having a wavelength shorter than the selective reflection wavelength band in the cholesteric liquid crystal layers 2 and 3 is used as excitation light for the dye 5.

  When causing laser oscillation in the laser oscillation element 1, first, the excitation light is incident on the cholesteric liquid crystal layer 2, for example. Then, the excitation light is transmitted through the cholesteric liquid crystal layer 2 and is incident on the defect layer 4 to excite the dye 5 to cause fluorescence emission and cause laser oscillation. At this time, the laser oscillation element 1 can cause laser oscillation with high efficiency. In other words, the laser oscillation element 1 can oscillate a sufficiently high intensity laser beam even if its thickness is small.

  Here, the laser oscillation occurs with high efficiency in the defect layer 4, and the transition moment of the dye is aligned parallel to the surfaces of the cholesteric liquid crystal layers 2 and 3. This may be because the extraction efficiency is sufficiently high.

  Further, according to the laser oscillation element 1, it is possible to cause continuous laser oscillation.

  In the above embodiment, the spiral direction of the cholesteric liquid crystal layers 2 and 3 is set to the left, but if the spiral direction of the cholesteric liquid crystal layers 2 and 3 is the same, the right direction It may be.

  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 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 Shin Nippon Oil Co., Ltd.) was used. A molecular cholesteric liquid crystal solution was obtained. Here, the mixing ratio of the polymer chiral nematic liquid crystal in the liquid crystal mixture was 93 wt%, and the concentration of the mixture in the polymer cholesteric liquid crystal solution was 10 wt%.

  This polymer cholesteric liquid crystal solution was spin cast on a glass substrate having a polyimide alignment film (1254 manufactured by JSR Corporation) rubbed in one direction, and then heated to 180 ° C. for 2 minutes by curing the cholesteric liquid crystal solution. Processed. In this way, a polymer cholesteric liquid crystal (PCLC) film having a thickness of about 1.8 μm that was well oriented was obtained on a glass substrate. At this time, the helical axis of the PCLC film was perpendicular to the glass substrate surface.

  Next, a spacer having a thickness of 12.5 μm made of polyethylene terephthalate (PET) is added to the two PCLC films so that the directors of the cholesteric liquid crystal on the surface are parallel to each other and the PCLC film is disposed inside. Connected through.

  On the other hand, a commercially available low molecular weight mixture of nematic liquid crystals (NLC) (ZLI 2293 manufactured by Merck) and fluorescent polymer dye (Journal of Chemical Society, 2002, No. 124, p. 9670). A mixture with the chemical structural formula described in (when R = EtH, R ′ = t-Bu, the molecular weight is 8100, and the weight average molecular weight Mw / number average molecular weight Mn is 2) is mixed in chloroform. Thus, a dye-doped NLC solution was prepared. At this time, the concentration of the polymer dye in NLC was set to 2 wt%.

  Thereafter, the dye-doped NLC solution was introduced into the space between the PCLC films using capillary action, and chloroform was evaporated at 70 ° C. to form a defect layer. Thus, a laser oscillation element having a thickness of 16.1 μm was obtained.

(Example 2)
The laser oscillation element was the same as that of Example 1 except that the chiral nematic mixing ratio in the liquid crystal mixture was 92 wt% and only the thickness of the defect layer was changed to 6 μm to change the thickness of the laser oscillation element to 9.6 μm. Got.

(Example 3)
The laser oscillation element was the same as that of Example 1 except that the chiral nematic mixing ratio in the liquid crystal mixture was 87 wt% and only the thickness of the defect layer was changed to 2 μm to change the thickness of the laser oscillation element to 5.6 μm. Got.

Example 4
A laser oscillation element was obtained in the same manner as in Example 1 except that the thickness of the laser oscillation element was 2 μm.

(Comparative Example 1)
A laser oscillation element was obtained in the same manner as in Example 1 except that one of the two PSLC films and the defect layer were removed.

(Measurement of fluorescence spectrum, reflection spectrum and laser oscillation)
The laser oscillation elements obtained in Examples 1 to 3 were measured for fluorescence spectrum, reflection spectrum and laser oscillation. The results are shown in FIGS. 2A to 2C, the broken line corresponds to the fluorescence spectrum, the alternate long and short dash line corresponds to the reflection spectrum, and the solid line corresponds to laser oscillation.

  In the measurement of fluorescence spectrum and laser oscillation, a 435 nm pulse laser beam emitted from an optical parametric oscillator (OPO) was used as excitation light. For the excitation of OPO, a third harmonic emitted from an Nd: YAG laser was used.

  The excitation light was incident obliquely (about 30 °) with respect to the glass substrate surface of the laser oscillation element. Light emitted from the laser oscillation element was detected by a multichannel spectrometer (USB 2000 manufactured by Ocean Optics) with a lens arranged in front of the glass substrate, that is, on the normal line to the surface of the glass substrate.

  The reflection spectrum was measured with a microscope spectrometer (ORF-made TFM-120AFT-PC).

  From the results shown in FIGS. 2A to 2C, when the transition moment of the dye is oriented parallel to the surface of the PCLC film in the defect layer between the PCLC films, the thickness of the laser oscillation element Despite being small enough, high-intensity laser oscillation was confirmed.

  In the laser oscillation element of Example 1, as shown in FIG. 2A, the reflection spectrum overlaps with the fluorescence spectrum, the laser oscillation wavelength (emission peak wavelength) is 508 nm, and FWHM (full width of Half). Maximum) was about 3 nm. Further, in the laser oscillation element of Example 2, as shown in FIG. 2B, the reflection spectrum is slightly deviated from the fluorescence spectrum, and the laser oscillation wavelength (long wavelength side) of the two laser oscillation wavelengths due to the defect layer. Wavelength) was 523 nm, and FWHM was 15 nm or less. Furthermore, in the laser oscillation element of Example 3, as shown in FIG.2 (c), the reflection spectrum shifted | deviated from the fluorescence spectrum, the laser oscillation wavelength was 520 nm, and FWHM was 2.5 nm. However, in the laser oscillation element of Example 3, the skirt portion of the emission peak was broad.

The reflection spectrum of the laser oscillation element obtained in Comparative Example 1 was measured in the same manner as in Example 1 and compared with the result of the reflection spectrum for the laser oscillation element of Example 2. The results are shown in FIG. In FIG. 3, the solid line corresponds to Example 2, and the alternate long and short dash line corresponds to Comparative Example 1 .

  From the result shown in FIG. 3, the reflectance of the laser oscillation element of Example 2 is sufficiently larger than the reflectance of the laser oscillation element of Comparative Example 1, and in addition, in the reflection spectrum according to Example 2, there is It can be seen that the reflectance greatly exceeds 50% at the wavelength.

  In the reflection spectrum, selective reflection by cholesteric liquid crystal generally contributes to a portion having a high reflectance. The selective reflection reflects 50% of circularly polarized light of incident light and transmits the remaining 50% of circularly polarized light. For this reason, the reflectance exceeding 50% means that there is a structural factor that increases the reflected light intensity in the laser oscillation element of the second embodiment.

Therefore, in order to investigate the structural factors that increase the reflected light intensity in the laser oscillation element of Example 2, a simulation experiment was performed on the reflection spectrum of the following three types of laser oscillation elements using MATLAB 6.1 manufactured by Cybernet System Co., Ltd. It was.
(1) Laser oscillation element composed of only a single cholesteric liquid crystal film (2) Laser oscillation element provided with an isotropic defect layer between two cholesteric liquid crystal films (3) Anisotropy between two cholesteric liquid crystal films Laser Oscillator with Defect Layer Here, the simulation conditions were set as follows.

(I) a cholesteric liquid crystal film _{n e = 1.63, n o =} 1.5
Thickness = 1.35μm
Helix pitch = 510nm
(Ii) Anisotropic defect layer n _e = 1.66, n _o = 1.5
Thickness = 1.2 μm
(Iii) Isotropic defect layer n _e = 1.56, n _o = 1.56
Thickness = 1.2 μm
The result of the simulation experiment is shown in FIG. In FIG. 4, the solid line corresponds to (3), the alternate long and short dash line corresponds to (2), and the alternate long and two short dashes line corresponds to (1).

  From the result of FIG. 4, it can be seen that the reflectance in the selective reflection band is particularly larger in the laser oscillation element (3) than in the laser oscillation elements (1) and (2). From this, it is considered that the defect layer made of an anisotropic medium contributes to the improvement of the reflectance.

  From the results of Examples 1 to 3 above, it was found that the laser oscillation occurred with high efficiency according to the laser oscillation element of the present invention.

  It was also found that the overlap between the reflection spectrum (selective reflection wavelength band) and the fluorescence spectrum (fluorescence emission band) is important for causing laser oscillation that emits a sharpened emission peak.

  Next, for the laser oscillation element obtained in Example 4, for the purpose of examining the minimum value (threshold value) of incident energy necessary for laser oscillation, the excitation light source is emitted from a He—Cd (helium-cadmium) laser at 442 nm. Changed to continuous light.

  A rotating neutral density filter was installed immediately after the He-Cd laser exit, allowing continuous adjustment of the incident energy (light quantity) to the laser oscillator.

  The excitation light transmitted through the neutral density filter was incident obliquely (about 30 °) with respect to the glass substrate surface of the laser oscillation element. Light emitted from the laser oscillation element was detected with a multichannel spectrometer (USB 2000 manufactured by Ocean Optics) using a lens arranged in front of the glass substrate, that is, on the normal line to the surface of the glass substrate.

FIG. 5 shows the emission light spectrum with respect to the incident energy, and FIG. 6 shows the relationship between the incident energy and the light intensity of the maximum peak of light emission from the laser oscillation element. In addition, the small graph shown in FIG. 6 is a graph which shows the change of the maximum peak intensity | strength of light emission in the area | region where incident energy is low, and expands and shows the scale. The unit of the horizontal axis is W / cm ² , and the unit of the vertical axis is an arbitrary unit.

FIG. 6 shows that the incident energy and the emitted light have a substantially linear relationship. In particular, even in a low energy region where the incident energy is less than 0.1 W / cm ^2, a peak inherent to laser oscillation is recognized in the emitted light. It was confirmed that continuous laser oscillation occurred without a threshold of incident energy.

It is sectional drawing which shows roughly one Embodiment of the laser oscillation element which concerns on this invention. It is a graph which shows the measurement result of the fluorescence spectrum which concerns on the laser oscillation element of Examples 1-3, a reflection spectrum, and a laser oscillation. 6 is a graph showing reflection spectra of laser oscillation elements according to Example 2 and Comparative Example 1. It is a graph which shows the simulation result of the reflection spectrum of the laser oscillation element of three types of structures. 6 is a graph showing an emitted light spectrum with respect to incident energy for a laser oscillation element according to Example 4. 10 is a graph showing the relationship between incident light and outgoing light peak intensity for a laser oscillation element according to Example 4.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Laser oscillation element, 2 ... Cholesteric liquid crystal layer (1st cholesteric liquid crystal layer), 3 ... Cholesteric liquid crystal layer (2nd cholesteric liquid crystal layer), 4 ... Defect layer, 5 ... Dye, 6 ... Nematic liquid crystal.

Claims (1)

A first cholesteric liquid crystal layer containing cholesteric liquid crystal;
A second cholesteric liquid crystal layer disposed opposite to the first cholesteric liquid crystal layer and containing cholesteric liquid crystal;
A defect layer that is provided between the first cholesteric liquid crystal layer and the second cholesteric liquid crystal layer and includes a dye that emits fluorescence by photoexcitation;
The selective reflection wavelength band in the cholesteric liquid crystal and the emission band of fluorescence emitted from the dye overlap in at least a part of the wavelength region,
The spiral direction of the cholesteric liquid crystal contained in the first cholesteric liquid crystal layer and the second cholesteric liquid crystal layer is the same,
The transition moment of the dye is aligned parallel to the surfaces of the first cholesteric liquid crystal layer and the second cholesteric liquid crystal layer ;
The first cholesteric liquid crystal layer and the second cholesteric liquid crystal layer include a director of a cholesteric liquid crystal on the surface of the first cholesteric liquid crystal layer on the defect layer side, and a cholesteric on the surface of the second cholesteric liquid crystal layer on the defect layer side. A laser oscillation element, wherein the liquid crystal directors are arranged in parallel to each other .

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