CA2122428A1 - Process for the production of materials having good nonlinear-optical properties - Google Patents

Abstract

The present invention relates to a process for the production of materials having good, structurable nonlinear-optical proper-ties, and to the use of these materials.
The process comprises subjecting materials having a liquid-crystalline matrix simultaneously to an electric field and unpolarized and/or circular-polarized light at temperatures below their glass transition temperature.
The process enables the production of structured samples having good nonlinear-optical properties.

Description

Docket: CO 9301 21 2 212 8 Paper No. 1 PRO OESS FOR THE PRODUCTION OF M~R~TAr~ HAVING
GOOD II~P~.TNl~A~--OPTI~'~T~ PRO~

Field of Invention The present invention relates to a process for the production of materials having good, structurable and microstructurable nonlinear-optical properties, and to the use of these materials.
Backqround of Invention Nonlinear-optical materials are used in microelectronics (optical switches, integrated circuits, frequency doubling and tripling). They are required for frequency doubling since few high-power lasers in the visible and in particular the ultra-violet spectral region are available. For example, frequency doubling of the Nd/YAG laser (A= 1064 nm) which is frequently encountered gives a light ~eam in the green spectral region (532 nm).
Customary materials known for frequency doubling are inorganic materials such as potassium dihydrogenphosphate (KDP), urea or LiNbO3. These materials have only low molecular hyper-polarizabilities ~. However, high hyperpolarizabilities ~ are the molecular prerequisite for the generation of frequency-doubled light. The generation of frequency-doubled light is also known as second harmonic generation or SHG. The quality of the material employed for frequency doubling is attained from the strength of the SHG signal. Further details on the theory of nonlinear optics are given, for example, in K. D. Singer, Electroresponsive Mol.
Polym. Syst., (1991), 2, 49-112.

212242~
-- In macroscopic samples, the quantity corresponding to the molecular hyperpolarizability ~, the susceptibility ~(2), can be measured. The magnitude of this susceptibility has a considerable effect on the conversion efficiency ~ of the laser light in the second harmonic wave (equations 1-3).
~ = P(2~)/P(~) (l) P(2w) = (2~2~(2)212)/(~Oc3n~2n2~2wo2)*p2(~)*s (2) X(2) = NFD~ (3) ~ = conversion efficiency P(i~) - power of the ith harmonic wave ~(2) = second order susceptibility ni~ = refractive index of the ith harmonic wave wO = ray diameter l = sample thickness S = phase matching factor N = molecule density F = field factor D = alignment factor ~ = molecular hyperpolarizability Another important factor for the conversion efficiency ~ is the alignment parameter D of the molecules. The alignment parame-ter D depends on the quality of poling. The better the poling, the greater the alignment parameter D (maximum 1). Poling is taken to mean the alignment of the assymetrical molecules in such a way that all dipoles point in the same direction, giving overall a non-centrosymmetrical structure.
In inorganic materials, such as KDP, only a low molecular hyperpolarizability ~ is found, but monocrystals of high order (large alignment factor D) and largeX (2) can be obtained from these compounds.

_ organic materials having a large molecular hyperpolariza-bility ~ are known, for example, from D. M. Burland, SPIE (1991), 1560, 111-119. However, there has been no success in obtaining a good degree of alignment in these materials, at least over several months.
H. Man, Adv. Mater., (1992), 159-168, discloses that polymers doped with nonlinear-optical molecules can be poled by means of strong electric fields or corona poling at temperatures above the glass transition temperature (Tg) of the polymers. It is disad-vantageous that this alignment is continuously lost on removal of the electric fields. A further disadvantage of this method is that the poling must be carried out at the high temperatures above Tg. A further disadvantage is that the method described here allows exclusively large-area poling of the entire element in a simple manner. Production of structurable and microstructurable elements is not possible.
A further process (Z. Sekkat, M. Dumont, Appl. Phys. B, 54, 486-489 (1992)) effects poling using the effect that NL0 chromo-phores, mixed into an isotropic matrix, can be poled with their long axis in the ray direction by irradiation with circular-polar-ized light after application of a direct-voltage field. The samples obtained by this process - NL0 chromophores in PMMA as non-liquid-crystalline medium - exhibit good SHG signals, but these have only low stability. After removal of the electric field, the SHG signal drops back to a low residual value after a few seconds due to relaxation of the molecules in the isotropic matrix.
Description of Invention The present invention relates to a process for the production of materials having good nonlinear-optical properties, which _ comprises subjecting materials containing a liquid-crystalline matrix simultaneously to an electric field and unpolarized and/or circular-polarized light at below their glass transition tempera-ture.
Surprisingly, it has been found that simultaneous irradiation of materials having a liquid-crystalline matrix with circular-polarized and/or unpolarized light and application of an electric field below Tg gives samples having strong SHG signals which remain stable even after the light source and the electric field have been switched off.
The process according to the invention enables poling below the glass transition temperature of the sample, which on the one hand is gentler on the material and on the other hand gives samples with less-scattering structures and thus better optical quality. The light is frequency-doubled by the process according to the invention with similar efficiency as in the case of pure field poling, without the disadvantages associated with field poling occurring.
Materials which are suitable for the process according to the invention must have a liquid-crystalline matrix. Amazingly, the liquid-crystalline matrix stabilizes the poled structure far better than isotropic or amorphous materials. The materials suit-able according to the invention are polymers, such as, polymeth-acrylates, polyacrylates, polysiloxanes, polyvinyl compounds, polyethers and polyesters, having a liquid-crystalline phase, for example a nematic, smectic or cholesteric phase. The liquid-crys-talline phases in these polymers are built up by means of meso-genic compounds, as disclosed, for example, in U.S. 4,388,453.
The mesogenic radicals disclosed in U.S. 4,388,453 are hereby incorporated by reference.

_ The materials must have the following properties:
(a) they must have at least one chromophoric group which can be excited by suitable light and, through photo physical processes, for example cis/trans isomeriza-tion, enables realignment of the liquid-crystalline matrix into a homeotropic structure;
(b) they must have at least one chromophoric group of high molecular hyperpolarizability ~;
(c) they must have a glass transition temperature above room temperature (20C), preferably above 50C.
The chromophoric group for isomerization and the chromophoric group of high molecular hyperpolarizability may have been incorpo-rated into one molecule, but may just as easily be present in different molecules, independently of one another. The chromo-phoric groups may, optionally, be covalently bonded to the poly-mer.
The production of suitable materials is described, for example, in R. Ortler, Makromol. Chem., Rapid Commun. 10, 189-194 (1989), or in U.S. 4,410,570.
Examples of suitable materials are polysiloxanes such as, polyalkylsiloxanes, for example polymethylsiloxanes, substituted by liquid-crystalline groups.
Particularly suitable are cyclic polysiloxanes having choles-teric properties, particularly those containing mesogenic groups having cholesteric, photoreactive and NLO-active properties and having slass transition temperatures of between S0C and 60C and clearing points of between 180C and 200C. Further preference is given to cyclic polysiloxanes containing 4-amino-4'-nitroazoben-zene or 4-amino-4'-cyanoazobenzene as nonlinear-optical groups.

_ Said materials are introduced into a cell coated with IT0 (IT0 = indium/tin oxide) by capillary forces at a temperature between the glass transition temperature and the clearing point by customary processes of display technology, as described, for example, in H. Man, Adv. Mater., (1992), 159-168. Conditioning, preferably at from 140C to 160C for from 1 to 3 hours, gives an optically clear phase in which the helix axis is perpendicular to the glass surface. The long axis of the molecules is aligned parallel to the glass plates.
A thin coating of the starting material is produced by spin-coating, for example on a glass plate, by another known process.
To this end, the material is applied as a dilute solution to an ITO-coated glass plate and rotated on a heatable turntable until the solvent has evaporated. An optically clear phase is subse-quently produced by conditioning as described.
According to the invention, after the material has been cooled to a temperature below the glass transition temperature, the starting material is exposed to unpolarized light and/or to circular-polarized light. Suitable light sources for unpolarized light are all known light sources which produce such light.
Preference is given to a mercury/xenon lamp. Suitable light sources for circular-polarized light are all known light sources which produce such light. Preferably suitable are lasers, for example an Kr+ ion laser.
The irradiation is preferably carried out at an intensity of from 10 mW/cm2 to 1000 mW/cm2, particularly preferably at an intensity of 150 mW/cm2 to 300 mW/cm2, for a period depending on the irradiation intensity, preferably for up to 5 days.

The irradiation is carried out perpendicular to the sample surface. The wavelength of the irradiation light must be selected so that excitation of the photochromic compound by the irradiation light is possible.
During the irradiation with unpolarized and/or circular-polarized light, an electric field is, according to the invention, additionally applied to the samples. The electric field is aligned parallel to the light. The electric field should prefera-bly have a strength of from 1 V/~m to 100 V/~m, more preferably from 10 V/~m to 50 V/~m.
The long-term stability at room temperature of the alignment of the materials aligned, according to the invention, after the irradiation light and the electric field have been switched off was checked by monitoring the SHG signal. The samples exhibited only a slight drop, due to relaxation, of the SHG signal directly after poling to about 70% of the initial value. This was not followed by any further decrease in the SHG signal, so that relaxation processes are unimportant even over relatively long periods. Neither irradiation with unpolarized or circular-polar-ized light alone nor application of an electric field alone cause poling below Tg.
If the aligned samples are warmed to above the glass transi-tion temperature, the alignment of the sample is eliminated again and a SHG signal is no longer found. This process can be utilized for reversibly switching the SHG signal on and off.
The simultaneous use of circular-polarized and/or unpolarized light and an electric field opens up the possibility of the pro-duction of structured samples.
Structured samples can be produced in a simple manner by subjecting the sample, at below the glass transition temperature of the materials having a liquid-crystalline matrix, simulta-neously to an electric field and to structured irradiation by unpolarized and/or circular-polarized light. The samples are preferably produced by laying at least one mask on the sample during the exposure. This means that poling only takes place in the exposed areas. Other location-dependent irradiation techni-ques, such as, laser scanning, are likewise possible for this process.
The maximum achievable resolution during structuring is determined by the wavelength of the light used.
Structured samples can be produced by two variants of the process according to the invention:
1. The electric field is applied over the entire surface, and only certain areas are irradiated. In this procedure, a homeotropic structure with poled NLO chromophores forms in the exposed areas. The original liquid-crystalline structure is retained in the unexposed areas.

2. The irradiation is carried out over the entire surface and the electric field is only applied to certain areas. In this procedure, a homeotropic structure with poled NLO chromo-phores forms in the areas. A homeotropic, but unpoled struc-ture forms in the voltage-free areas.
The process according to the invention thus also enables the production of structured waveguides and optical switching elements having good nonlinear properties.
Fig. 1 shows the angle-dependent SHG signal for the realign-ment methods described in the examples. [r.u.] represents random units.

2122~28 - Fig. 2 shows the change in SHG intensity of the sample from Example 8 with time.
The following examples serve to further illustrate the inven-tion:
Example 1 Preparation of 4-(N-2-propenyl-N-ethyl)amino-4'-nitroazobenzene a. Preparation of N-ethyl-N-allylanilin 0.2 mole of bromo-1-propene are carefully added dropwise to 0.2 mole of N-ethylanilin, and the solution is subse-quently heated at 100C for 20 hours. After cooling, 200 ml of water are added to the solidified reaction material, and solid potassium hydroxide is added with vigorous stirring until the solution remains alkaline.
The organic phase is separated off, dried over sodium sulfate and subjected to fractional vacuum distillation.
b. Diazotization A solution of 3.15 g (45 mmol) of sodium nitrite in 10 ml of water is added in one portion at 0C - 5C to a suspension of 30 mmol of 4-nitroanilin, 10 ml of concen-trated hydrochloric acid and 25 ml of water. The sodium nitrite solution is added under the surface of the sus-pension, during which the temperature may briefly rise to 15C. The mixture is subsequently stirred at 0C -5C for 1 hour, and the resultant diazonium salt solu-tion is filtered.
c. Coupling The diazonium chloride solution prepared is added in portions to a solution, cooled to 0C - 5C, of 30 mmol of N-ethyl-N-allylanilin, 21 g of sodium acetate, 17 ml of glacial acetic acid and 200 ml of water at such a _ rate that the stated temperature range is not exceeded.
The resultant suspension is subsequently stirred for an additional 2 to 3 hours, and the precipitated solid is filtered off with suction and dried. The resultant crude product is purified by recrystallization from ethanol. Recrystallization from ethanol gives 5.1 g (55%) of dark-red leaves of melting point of 108C -110 C .
Example 2 Preparation of 4-(N-4-pentenyl-N-ethyl)amino-4'-cyanoazobenzene a. Preparation of N-ethyl-N-pentenylanilin 0.2 mole of bromo-l-pentene is carefully added dropwise to 0.2 mole of N-ethylanilin, and the solution is subse-quently heated at 100C for 20 hours. After cooling, 200 ml of water are added to the solidified reaction material, and solid potassium hydroxide is added with vigorous stirring until the solution remains alkaline.
The organic phase is separated off, dried over sodium sulfate and subjected to fractional vacuum distilla-tion.
b. Diazotization A solution of 3.15 g (45 mmol) of sodium nitrite in 10 ml of water is added in one portion at 0C - 5C to a suspension of 30 mmol of 4-aminobenzonitrile, 10 ml of Z5 concentrated hydrochloric acid and 25 ml of water. The sodium nitrite solution is added under the surface of the suspension, during which the temperature may briefly rise to 15C. The mixture is subsequently stirred at 2122~28 _ 0C - 5C for 1 hour and the resultant diazonium salt solution is filtered.
c. Coupling The diazonium chloride solution prepared is added in portions to a solution, cooled to 0C - 5C, of 30 mmol of N-ethyl-N-pentylanilin, 21 g of sodium acetate, 17 ml of glacial acetic acid and 200 ml of water, at such a rate that the stated temperature range is not exceeded.
The resultant suspension is subsequently stirred for an additional 2 to 3 hours, and the precipitated solid is filtered off with suction and dried. The resultant crude product is purified by recrystallization from petroleum ether. Recrystallization gives 4.7 g (49%) of orange crystals of melting point 63C - 64C.
Example 3 Preparation of liquid crystals using 4-(N-2-propenyl-N-ethyl)-amino-4'-nitroazobenzene 0.97 g (4.03 mmol) of tetramethylcyclotetrasiloxane, 2.40 g (7.25 mmol) of 4'-phenyl 4-(propen-2-oxy)benzoate, 3.98 g (7.25 mmol) of cholestanyl 4-(propen-2-oxy)benzoate (the pre-paration of these substances is described in U.S. 4,410,570) and 0.50 g (1.61 mmol) of 4-(N-2-propenyl-N-ethyl)amino-4'-nitroazobenzene are dissolved in 20 ml of dry toluene, 0.08 ml of a solution of dicyclopentadienylplatinum dichloride (1%
by weight in methylene chloride) is added, and the mixture is warmed at 100C for 1 hour. When the reaction is complete, the catalyst is separated off via a short silica gel-filled column (1 = 3 cm, diameter = 3 cm), and the product is preci-pitated a number of times from ethanol until the residual 2122~28 _ monomer content is below 1%. The end product is filtered through a 0.2~m filter and dried at 90C in vacuo, giving 2.5 g (32%) of a substance having a reflection wavelength of 1176 nm. The substance has a glass transition temperature of 59C and a clearing point of 180C.
Example 4 Alignment and poling of the sample by means of circular-polarized light and electric field at temperatures below Tg The liquid-crystalline polysiloxane from Example 3 is intro-duced at 140C by means of capillary forces into an ITO-coated, commercially available cell (d = 5~m) (E.H.C. Co., Ltd., Tokyo). Conditioning (160C, 60 min) gives an opti-cally clear phase in which the helix axis is perpendicular to the glass surface. The long axis of the molecules is aligned parallel to the glass plates. Irradiation of the sample with circular-polarized light from a Kr+ ion laser (482 nm, 200 mW/cm2) at 53C (T < Tg) aligns the sample homeotropically, and simultaneous application of an electric field (5 V/~m) poles the sample. The circular-polarized light and the electric field are switched off.
In order to investigate the poling, frequency-doubled light is produced by means of an Nd/YAG laser (1064 nm), and the angle-dependent intensity of the frequency-doubled light is detected with the aid of the Maker interference method (P.D.
Maker, Phys. Rev. Lett. 8, 21 (1962)) (Fig. l.II). The measurement gives an SHG signal of 1.2 (random units).

- Comparison Example 1 Alignment and poling of the sample by means of electric fields at temperatures about Tg The liquid-crystalline polysiloxane from Example 3 is intro-duced at 140C by means of capillary forces into an IT0-coated, commercially available cell (d = 5~m) (E.H.C. Co., Ltd., Tokyo). Conditioning (160C, 60 min) gives an opti-cally clear phase in which the helix axis is perpendicular to the glass surface. The long axis of the molecules is aligned parallel to the glass plates. Warming to 100C (T > Tg) and application of an electric field (21 V/~m) poles the sample.
The sample is cooled, and the electric field is then switched off.
In order to investigate the poling, frequency-doubled light is produced by irradiating the sample with the aid of an Nd/YAG laser (1064 nm). The angle-dependent intensity of the frequency-doubled light is detected with the aid of the Maker interference method (Fig. l.I). The measurement gives an SHG
signal of 0.75 (random units).
Comparison Example 2 Alignment and poling of the sample by means of electric fields at temperatures below Tg The liquid-crystalline polysiloxane from Example 3 is intro-duced at 140C by means of capillary forces into an IT0-coated, commercially available cell (d = 5~m) (E.H.C. Co., Ltd., Tokyo). Conditioning (160C, 60 min) gives an opti-cally clear phase in which the helix axis is perpendicular to the glass surface. The long axis of the molecules is aligned parallel to the glass plates. It is attempted to pole the sample by warming to 53C (T < Tg) and application of an electric field (21 V/~m). The electric field is switched off .
In order to investigate the degree of poling, the sample is irradiated with an Nd/YAG laser (1064 nm) in order to produce frequency-doubled light and to detect the angle-dependent intensity of the frequency-doubled light with the aid of the Maker interference method. No SHG signal can be measured, i.e., no poling of the sample by electric fields at tempera-tures below Tg takes place.
Comparison Example 3 Alignment and attempted poling of the sample by means of circular-polarized light The liquid-crystalline polysiloxane from Example 3 is intro-duced at 140C by means of capillary forces into an ITO-coated, commercially available cell (d = 5~m) (E.H.C. Co., Ltd., Tokyo). Conditioning (160C, 60 min) gives an opti-cally clear phase in which the helix axis is perpendicular to the glass surface. The long axis of the molecules is aligned parallel to the glass plates. It is attempted to pole the sample by warming to 53C (T < Tg) and irradiation with circular-polarized light from a Kr+ ion laser (482 nm, 200 mW/cm2). The light source is switched off.
In order to investigate the degree of poling, the sample is irradiated with an Nd/YAG laser (1064 nm) in order to produce frequency-doubled light and to detect the angle-dependent intensity of the frequency-doubled light with the aid of the Maker interference method. In this experiment, no SHG signal can be measured (Fig. l.III), i.e., no poling of the sample by irradiation with circular-polarized light from a Kr+ ion ~ laser (482 nm, 200 mW/cm2) takes place; the sample is aligned homeotropically, but the NL0 chromophore remains centrosym-metrical.
Example 5 Preparation of liquid crystals by means of 4-(N-4-pentenyl-N-ethyl)amino-4'-cyanoazobenzene 0.38 g (1.57 mmol) of tetramethylcyclotetrasiloxane, 0.93 g (2.83 mmol) of 4'-phenylphenyl-4-(propen-2-oxy)benzoate, 1.55 g (2.83 mmol) of cholesteryl 4-(propen-2-oxy)benzoate and 0.20 g (0.63 mmol) of 4-(N-4-pentenyl-N-ethyl)amino-4'-cyanoazobenzene are dissolved in 10 ml of dry toluene, 0.03 ml of a solution of dicyclopentadienylplatinum dichloride (1%
by weight in methylene chloride) is added, and the mixture is warmed at 100C for 1 hour. when the reaction is complete, the catalyst is separated off via a short silica gel-filled column (1 = 3 cm, diameter = 3 cm), and the product is pre-cipitated a number of times from ethanol until the residual monomer content is below 1%. The end product is filtered through a 0.2~m filter and dried at 90C in vacuo, giving 1.0 g (33%) of a substance having a reflection wavelength of 600 nm. The substance has a glass transition temperature of 55C and a clearing point of 195C.
Example 6 Alignment and poling of the sample by means of circular-polarized light and an electric field The liquid-crystalline polysiloxane from Example 5 is intro-duced at 140C by means of capillary forces into an IT0-coated, commercially available cell (d = 5~m) (E.H.C. Co., Ltd., Tokyo). Conditioning (160C, 60 min) gives an opti-cally clear phase in which the helix axis is perpendicular to 2122~28 the glass surface. The long axis of the molecules is aligned parallel to the glass plates. Irradiation with circular-polarized light from a Kr+ ion laser (482 nm, 200 mW/cm2) at 53C (T < Tg) aligns the sample homeotropically, and simulta-neous application of an electric field (21 V/~m) poles the sample. The circular-polarized light and electric field are switched off.
In order to investigate the poling, frequency-doubled light is produced by means of an Nd/YAG laser (1064 nm), and the angle-dependent intensity of the frequency-doubled light is detected with the aid of the Maker interference method. The measurement gives an SHG signal of 0.15 (random units).
Example 7 Preparation of liquid crystals by means of 4-(N-2-propenyl-N-ethyl)amino-4'-nitroazobenzene 1.94 g (8.06 mmol) of tetramethylcyclotetrasiloxane, 5.06 g (15.3 mmol) of 4'-phenylphenyl-4-(propen-2-oxy)benzoate, 8.38 g (15.3 mmol) of cholestanyl 4-(propen-2-oxy)benzoate and 0.50 g (1.61 mmol) of 4-(N-2-propenyl-N-ethyl)amino-4'-nitroazobenzene are dissolved in 20 ml of dry toluene, 0.08 ml of a solution of dicyclopentadienylplatinum dichlo-ride (1% by weight in methylene chloride) is added, and the mixture is warmed at 100C for 1 hour. when the reaction is complete, the catalyst is separated off via a short silica gel-filled column (l = 3 cm, diameter = 3 cm), and the product is precipitated a number of times from ethanol until the residual monomer content is below 1%.
The end product is filtered through a 0.2~m filter and dried at 90C in vacuo, giving 7.8 g (40%) of a substance having a - reflection wavelength of 1234 nm. The substance has a glass transition temperature of 58C and a clearing point of 192C.
Example 8 Determination of the long-term stability of the materials accord-ing to the invention The liquid-crystalline polysiloxane from Example 7 is intro-duced at 140C by means of capillary forcés into an ITO-coated, commercially available cell (d = 5~m) (E.H.C. Co., Ltd., Tokyo). Conditioning (160C, 60 min) gives an opti-cally clear phase in which the helix axis is perpendicular to the glass surface. The long axis of the molecules is aligned parallel to the glass plates. Irradiation of the sample with circular-polarized light from a Kr+ ion laser (482 nm, 200 mW/cm2) at 53C (T < Tg) aligns the sample homeotropically, and simultaneous application of an electric field (5 V/~m) poles the sample. The circular-polarized light and the electric field are switched off.
In order to investigate the poling of the sample, frequency-doubled light is produced by means of an Nd/YAG laser (1064 nm), and the angle-dependent intensity of the frequency-doubled light is detected with the aid of the Maker interference method. The measurement gives an SHG signal of 1.05 (random units).
Monitoring of the SHG signal with time shows a decrease in the signal to about 70% of the initial value due to relax-ation within the first 50 hours (see Fig. 2).
The signal subsequently remains stable, as measurements over 6 weeks confirmed.

~Example 9 Production of a structurable and microstructurable sample The liquid-crystalline polysiloxane from Example 3 is intro-duced at 140C by means of capillary forces into an ITO-coated, commercially available cell (d = 5~m). Conditioning gives an optically clear phase in which the helix axis is perpendicular to the glass surface. The long axis of the molecules is aligned parallel to the glass plates. The sample is subsequently covered by a hole mask (d = 2cm).
Irradiation with circular-polarized light from a Kr+ ion laser (482 nm, 200 mW/cm2) through the mask at 53C (T < Tg) aligns the sample homeotropically in the exposed area, and simultaneous application of an electric field (5 V/~m) poles the sample. The light and the electric field are subse-quently switched off.
In order to investigate the poling, frequency-doubled light is produced by means of an Nd/YAG laser (1064 nm), and the angle-dependent intensity of the frequency-doubled light is detected with the aid of the Maker interference method. The measurement gives an SHG signal of 1.2 [r.u.] in the exposed area, while no SHG signal can be measured in the areas covered by the mask and thus only exposed to the field.

Claims (8)

1. A process for the production of materials having good non-linear-optical properties, which comprises subjecting materials having a liquid-crystalline matrix simultaneously to an electric field and unpolarized and/or circular-polari-zed light at temperatures below their glass transition temperature.

2. A process as claimed in claim 1, wherein the materials having a liquid-crystalline matrix are cyclic polysiloxanes.

3. A process as claimed in claim 2, wherein the materials having a liquid-crystalline matrix are cyclic polysiloxanes having cholesteric properties.

4. A process as claimed in claim 2, wherein the materials having a liquid-crystalline matrix are cyclic polysiloxanes con-taining 4-amino-4'-nitroazobenzene or 4-amino-4'-cyanoazoben-zene as nonlinear-optical groups.

5. A process as claimed in claim 1, wherein irradiation is carried out at an intensity of from 10 mW/cm2 to 1000 mW/cm2.

6. A process as claimed in claim 1, wherein an electric field having a strength of from 1 V/µm to 100 V/µm is applied.

7. A process for the production of structured samples having good nonlinear-optical properties, containing materials having a liquid-crystalline matrix, which comprises sub-jecting these samples having a liquid-crystalline matrix simultaneously to an electric field and to structured irradi-ation by unpolarized and/or circular-polarized light at temperatures below the glass transition temperature of the materials.

8. A process as claimed in claim 7 for the production of optical switching elements or structured waveguides.