DE2610052A1 - METHOD AND EQUIPMENT FOR DETERMINING ASYMMETRIES IN CRYSTALS IN A POWDER-MADE SAMPLE - Google Patents

Description

Registration from: March 10, 1976

Method and device for determining asymmetries in the crystals in a powdery sample

The invention relates to a method and a device for the determination of asymmetries in the crystals in a powdery sample. In particular, the invention is suitable for measuring possible electro-optical substances and for determining the 'absence of a crystallographic' symmetry center. The method "". "?"'-'"__ is essentially based on the irradiation of a sample with a high-power laser at a frequency to and on the measurement of the power generated at the 2nd harmonic at a frequency of 2

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ORIGINAL INSPECTgD

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A technique and device for evaluating non-linear optical materials are described in an article "A Powder Technique For the Evaluation of Non-Linear Optical Materials" by SK Kurtz and TT # Perry, which in "The Journal of Applied Physics ¹¹ , Volume 39, No. 8, pages 3798..3813 (July 1963). Further work has shown that a detection sensitivity of at least 10 of the harmonics from a standard quartz powder sample to determine the asymmetry or symmetry of a material in a high (99 $>) Reliability level is required. This requires

h 5/2 work at nominal laser power densities of 10 to 10 W / cm, which normally do not cause any undesired visible optical signals. These signals are referred to in the literature in various ways as burns, plumes and laser damage. However, occur in a powder

these or similar effects; especially with the power levels on, which is for a reliable symmetry center determination: "tfesentlxch show .. 'This is the reliable-'

ability of this method! to detect asymmetry

on the approximate rait of the gearing slide ^ Pulyexprüfung _-----; ^:

(Journal of 'ApplJlPhys.; Banöf 39 .Nr. _8, p.3798 «.3813). ".

received value "limited"; determination of such from s er st

'Fine asymmetries is in both crystal structure determinations as well as very important when studying disturbances in phase transitions.

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The invention is based on the object of specifying a determination method that is highly reliable indicates whether a material is asymmetrical or symmetrical, is

This object of the invention is described below.

The invention is characterized in that only essentially a 2nd harmonic of the fundamental wave remains, with means for splitting the beam behind the sample into two beams, with a narrow band filter in the path of one of the two beams to constrain the frequency in said beam to substantially that ^, Harmonics, with means for balancing the intensities of the two rays on the frequency of the 2nd harmonic, with Means in the path of each of the aforementioned split beams for determining their intensity, and with means for Reproduction of the respective intensities of the mentioned

i!

Rays to determine the asymmetries of the sample.

For example, a flashlight becomes more active NdiGlas laser ("Λ = 1.06 / µm) with an optical energy of 1 joule and a pulse duration of 300 / us in injection

operation used .__ After._removing theJB.litzlich.t-., radiation With the help of a filter, the beam is focused on a powdery sample. When the sample crystallographic. is asymmetrical, becomes the 2nd harmonic

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ORfGlMAL INSPECTED

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the laser fundamental frequency ( ¹ ^) is generated. After removing the fundamental wave with the help of filters, this light of the 2nd harmonic (SHG) is split with a light splitter and this light reaches two filters to select the green (5300 S.) SHG light. This two-channel system is specially developed in this way that if all the light captured by the sample has a skin length ) = 53QO S. (SHG), balanced signals are displayed by the two photomultiplier units on an oscilloscope. This is done with a light splitter that splits the light in a ratio of one to two thirds. The first third goes directly to a photomultiplier. The two thirds pass a narrow band filter with 50% transmission on the wavelength of the 2nd harmonic before they reach a second photomultiplier. The signals from the photo fans are only equal to each other if all the light produced has the SHG length. . . ; '■

Two-channel reproduction is out of balance if part of the visible light is damaged by laser is caused, because in this case there will be a. Larger signal determined in the unfiltered reference channel.

This technique: enables the achievement of the required

Sensitivity of 10 of the harmonics from a + quartz powder standard sample which for high reliability

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is desirable while suppressing interference signals at the same time will. The detector device is therefore careful through the appropriate assembly of normal optical parts designed so that the device was used as a single wavelength spectrometer works with a high collecting effect.

An additional unique property of the system is the use of an optimal solid angle to collect the light of the 2nd harmonic in the photomultiplier. When the powder amounts to a liquid with a refractive index equal to that of the crystal of the 2nd harmonic are immersed, the light of the 2nd harmonic is collected with high efficiency. Another advantage is a noticeable reduction in the interference radiation for a given laser intensity.

If the crystal is in the form of a powder, the powder dissipates the second harmonic. A ver— . Mixing the powder with an oil with the same refractive index as the powder suppresses the scattering. By Varying the refractive effect of the liquid is the Scatter regulb, aj? ..; When the creation of the 2nd harmonic; is determined with a detector with a fixed calibration,. ".." '_

"You can quantitatively determine the differences between the spread of the (SHG) be measured. The detected signal is included

■ the resultant of the simultaneously measured non-linear (SHG) and the linear scatter. The detected signal

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has a peak when the refractive index is the Liquid is almost equal to the refractive index of the powder. For birefringent crystals a medium one is used Index measured.

This method enables the simultaneous determination of the occurrence of crystalline Nxcjit — Centro— symmetry, the size of the powder mean value of the nonlinear optical coefficients and the refractive index and the birefringence of the mixture. Because the upper layer of the powder is unaffected by the multiple scattering is, a peak appears when index adjustment is made even for the material mix side. This effect makes it possible to use the linear and non-linear properties of this technique identify a mixture even when mixed with a second material of unequal refractive index.

The invention is explained in more detail below with reference to a few examples shown in the drawings. Show it:

Fig ^.; . 1 a Schäjjimngdiagram of the analyzer for determining / the 2nd harmonic,

'..'. Fig * \ £ a section through the "analyzer, ... ^ Fig. 3V the" relationship between "is ~ cHen ~ & er 'SXgriälintensität and the attenuation,

Fig. Das.Verhältnis h the intensity of the 2 harmonics as a function of the refractive index mismatch, and

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Flg. 5 appears to be a setup for performing of the method according to the invention with the aid an index adjustment medium.

In FIG. 1, a neodymium glass laser 1, when excited, generates a visible flash of light together with infrared at a wavelength of 1.06 μm, which a lens 2 directs in parallel. Visible light is removed by a first filter 3, which leaves only 1.06 μm and other infrared radiation which is attenuated by gray filters H , after which it is reflected by a mirror 5 and applied by a lens 6 to a sample 7 in. A sample holder 8 in a sample chamber is focused. '. '

If the sample is not crystallographically centered, the 2nd harmonic (2US) of the laser fundamental wave frequency (tv>) is generated, ie a 2nd harmonic is generated at 0. ^ 3 / vim. After removing the fundamental wave and other infrared radiation with the help of a second

<' '■■■ · ■

Filters 10, a light splitter 11 divides this 2nd harmonic (sHG), which are then connected to two photo multipliers 12 and 13

arrives, ■ ■ · ■ ' ■. ■ ; .

■ '": -'" '; --- ■ - The radiation in the -LixihtteilerTallende.Radiation is-so divided that-Bs ~ nsin thirdr (V / 3) nien- PhötöverylelTacher 12 ~

(see Fig. 2) and two thirds (2/3) to the • Photomultiplier, 13 captured. Between the light divider and the photomultiplier 13 is located, a narrow band

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ORIGINAL INSPECTED

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filter 14 with 50% transmission at 0.53 / um _ + 150 A, "If, therefore, only the 2nd harmonic is present, receive the photomultiplier 13 only receives a third of the incoming light from the sample,

The output signals of each of the photomultiplier compartments 12 and 13 are expediently displayed on an oscilloscope 15, the signal from the photomultiplier 12 being a reference signal. If all the light received from the sample has a wavelength λ = 5300 R (SHU), balanced signals from the two photomultiplier units are displayed on the oscilloscope.

Two-channel reproduction is unbalanced when visible light is generated by laser damage because in this case the unfiltered reference channel detects a larger signal,

For optimal detection of the SHG, it is not possible to increase the power density of the laser with powder as desired. 3 shows the SHG 30 and StSrsignale 31 as a function of the attenuation (gray value) in the laser beam for several different ones. Laser beam diameter (for powder). It is "- clear that there is an optimal focusing of the beam. For the laser of 1 joule and 300 / us used, this optimum is close to 3 now diameters for the powder sample, an additional unique advantage of the

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System is the use of an optimal solid angle to capture the light of the 2 »harmonics in the photomultiplier. If the powder quantities are immersed in a liquid with a refractive index equal to the index of the crystal at the 2 »harmonic, the light of the 2» harmonics is collected with high efficiency. Another advantage is a noticeable reduction in the interference radiation for a given laser intensity St, Fig. H shows a curve in which the intensity of the 2nd harmonic is plotted for the quartz reference in relation to the refractive index mismatch. The optimum collection solid angle is achieved that the active region of the Photovervielfacherkathode from the beam 2, Harmonisehen is filled with a customized index powder "The high sensitivity of the optical configuration for the refractive index mismatch (A η of 0.02 are pretty good detectable), as shown in Fig. 4, results in a practical aid for identification

i: ■ '·' ■

of the material that creates the 2nd harmonic «This is a major advantage that other nonlinear optical Configurations do not show »- It is thereby in a single function-both-the generation, the 2, harmonic vision" as well as a refractive index identification of the relevant Material (for example in a mixture) that the Harmonics created, united. This procedure is different

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(in a larger amount of information) from the conventional ones (Becke-Linie) Immersion methods for optical crystallography which do not have any means of distinguishing give centric and non-centric materials. For example, in a mixture of two materials A and B, the normal dipping process could determine the indices of refraction determine for A and B separately. Conventional SHG according to the description in the above-mentioned publication could only state that A or B (or both) are acentric are when SHG was detected. In this analyzer it is possible to measure the acentricity of one (or both) Materials by varying the index of the immersion oil and by determining the peak in the intensity of the 2nd harmonic ascertain. This is especially true in mineralogical and industrial samples significantly caused by undesirable impurities (including pollution) can give a misleading result in the amount of powder.

In a further embodiment according to the invention, particularly advantageous when the substance to be measured is in the form of a powder, the powder is mixed with a liquid whose refractive index; _'_. :: changes during the measurement and the signal of the "' Z " harmonics is detected by a fixed-range detector.

The change in the refractive index in the liquid can be achieved in several processes in one

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this procedure uses multiple samples with various commercially available index matching oils or others Liquids like methylene iodide (r ^ at 25 ° C, 1,737) prepared. Others are:

Methylene Iodide & Iodobenzene 1.715

ck -iodonaphthalene - 1,699

Ck -iodonaphthalene & <& -Bromonaphthalene 1,675

o-bromoiodobenzene 1,661

Phenyl isothiocyanate 1,647

s-tetrabromoethane 1.634

Iodobenzene 1,616

Bromoforra. 1,594

Aniline ■ 1,583

o-toluidine -. 1,569

Nitrobenzene 1 »5k9

Ethylene bromide 1.535

Propylene bromide 1.516

Pentachiorethane. . 1,501

Methyl pyrogenic acid salt ^: 1,485

Methyl thiocyanate '^:; 1,466

Isoamyl sulfide - - _. ..-.: ...—. - 1,451

Ethyl dichloroacetate "- ~~~ ~ - ~ - -—-..-""- ■ —---'-, 1.434 ethyl monochloroacetate 1.419

The above list is only part of the story. Many other liquids can be used.

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Another method is to use the Change in temperature of the refractive index as described by Hartshorne and Stuart, "Crystals and the Polarizing Microscope ", American Elsevier Publishing Co., New York (197O), page 433. According to this description the refractive index of some liquids changes with temperature and this property can be used as a Adjusting the refractive index of different materials use"

When carrying out the method according to the invention, in which a crystalline powder is used as the index matching medium, which is exposed in a holder 52 to the light at the frequency (Ό from a laser source 53. If the crystalline powder is not centrosymmetrical, a 2 »harmonic ( 2 ⁰ ^) of the fundamental wave, which harmonics are detected by an optical detector 5 ^ »ie a photomultiplier, a photodiode, etc. .. r · ■

If there is significant scattering, as indicated by the envelope curve 55, then the crystalline Powder mixed with a liquid whose refractive index is close to the refractive index of the powder. In this

\ Case, the envelope 56 represents the 2nd harmonic (2 U) ) generated by the sample and the detector captures a larger part of the radiation »

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In Pig. 4 shows measurements made with quartz, but crystalline material can also be used used, e.g. sucrose was also measured. If there is no non-centrosymmetry, there will be none 2, harmonics generated. If a 2nd harmonic is produced, a liquid with a refractive index close to that of the material can be used, otherwise the change described by Hartshorne and Stuart and mentioned above Liquids change their index of refraction with temperature and this principle can be used to distinguish between Use components of the material.

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Claims (5)

PHA.20708C. 02/23/76. - 14 - " 2 6 1 ü J b 2 PATENT CLAIMS / 1 ♦) Device for the determination of crystallograph.isch.er Asymmetries in a powdery sample with a Source of coherent radiation with a given fundamental wavelength and base intensity, with means for positioning the sample in the path of said radiation around the sample to expose this radiation, with means for removing the fundamental wave after traversing the sample, thereby marked that only essentially a 2 »harmonic of the fundamental wave remains, with means for splitting the beam behind the sample into two beams, with one Narrow band filter in the path of one of the two beams to the Limiting the frequency in the mentioned beam to essentially the 2nd harmonic, with means for balancing of the intensities of the two rays at the frequency of the harmonics, with means in the path of each of the mentioned ' split rays to determine their intensity, and with Means for playing the. relevant intensities of the mentioned rays for the determination of the asymmetries in the rehearsal ",:;, ■ ;. '!. 1 : 2. Device according to claim 1, characterized in that the sample is immersed in a liquid, which has a given index of refraction and thereby a maximum signal intensity generated. 809843/0719 original 3. Set up after. Claim 1, characterized in that the liquid has an index of refraction which is substantially equal to the index of refraction of the crystal at the 2 _o harmonic. 4β device according to claim 1, 2 or 3> characterized in that the sample is immersed in a matching medium with a variable refractive index, 5. Device according to claim 4, characterized in that that the refractive index of the matching medium is a function of its temperature. 6 »Device according to one of the preceding claims, characterized in that the radiation source activates a flash light he is Nd: glass laser. 7. Device according to one of the preceding address, characterized in that the narrow band filter has a 50% transmission characteristic and divides the mentioned dividing means in a ratio of one third to two thirds of the radiation intensity. ^; 809 843/0719. «*» ««. «8n * T« p