CN112903632B - Method for improving measurement accuracy of nonlinear optical coefficient of thin-film material - Google Patents
Method for improving measurement accuracy of nonlinear optical coefficient of thin-film material Download PDFInfo
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- CN112903632B CN112903632B CN202110089386.8A CN202110089386A CN112903632B CN 112903632 B CN112903632 B CN 112903632B CN 202110089386 A CN202110089386 A CN 202110089386A CN 112903632 B CN112903632 B CN 112903632B
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
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Abstract
The invention discloses a method for improving the measurement accuracy of nonlinear optical coefficients of thin-film materials, which selects materials with ultra-thin thickness and ultra-low nonlinear optical coefficients as the substrate of a thin-film element, and applies a double-arm Z scanning technology to simultaneously measure nonlinear signals of a thin-film device containing the substrate and a bare substrate.
Description
Technical Field
The invention relates to the technical field of interdisciplines of nonlinear optics, materials science and optoelectronics, in particular to a method for measuring a nonlinear optical coefficient of a thin-film material.
Background
Since the invention of laser in 1960, the nonlinear optics has been developed rapidly, and the interest of nonlinear optical characteristics of materials has been increased. The technical methods for measuring the nonlinear optical coefficient of the material mainly include a third harmonic method, a nonlinear interference method, a degenerate fourth harmonic method, a Z scanning method and the like.
In 1989, the group of M.Sheik-bahae subjects reported the Z scanning method for the first time, and the Z scanning technology is widely applied to nonlinear characteristic characterization experiments of materials due to the simplicity and high sensitivity of the Z scanning method. In 2019, the subject group firstly provides a method for testing the nonlinear optical coefficient of the thin-film material, namely the nonlinear signal of a substrate is removed by using a double-arm Z scanning technology, and only the nonlinear signal of the thin film is left, so that the measurement of the nonlinear optical coefficient of the thin-film material is realized.
The key for measuring the nonlinear optical coefficient of the thin-film material by the double-arm Z scanning technology is that a nonlinear signal of a thin-film device of a thin-film substrate and a nonlinear signal of a bare substrate have certain resolution. In a reported study [ appl.opt.58(13): D28(2019), the determination of the nonlinear coefficient of a 3 μm zno thin film plated on a 1mm quartz substrate was achieved by applying a two-arm Z-scan technique. In the research, the nonlinear signals of the film material are separated through the comparison of the signals of the two arms, but the nonlinear signals of the bare substrate are too large, so that the signals of the two arms are very close to each other, and the phenomenon has certain influence on the measurement precision of the final film material. In addition, for e.g. SiO2In general, due to the fact that the difference between the physical thicknesses of the thin film material and the substrate is large or the nonlinear coefficients of the thin film material and the substrate are close to each other, the nonlinear signal intensities of the thin film element and the bare substrate are too close to each other or even overlapped with each other, and therefore the accuracy of the measurement result cannot be guaranteed. Therefore, for thin film materials, besides the application of the dual-arm Z-scan technique, the appropriate substrate thickness and material type should be selected to effectively improve the measurement accuracy.
Disclosure of Invention
The invention provides a method for improving the measurement accuracy of nonlinear optical coefficients of thin-film materials, which selects materials with ultra-thin thickness and ultra-low nonlinear optical coefficients as the substrate of a thin-film element and combines a double-arm Z scanning technology to simultaneously measure nonlinear signals of the thin-film element containing the substrate and a bare substrate.
The technical solution of the invention is as follows:
a method for improving the measurement accuracy of the nonlinear optical coefficient of a thin film material selects a material with ultra-thin thickness and ultra-low nonlinear optical coefficient as a substrate of a thin film element, and applies a double-arm Z scanning technology to simultaneously measure nonlinear signals of the thin film element containing the substrate and a bare substrate.
The substrate materials of the two arms in the double-arm Z-scan test process have the same thickness and optical nonlinear coefficient.
The thickness of the substrate is less than or equal to 0.1 mm.
The nonlinear optical coefficient of the substrate is smaller than that of the film material.
The substrate material is MgF2、GaF2And the like.
The film-state material is ZnSe, ZnO or HfO2、SiO2、Al2O3And the like.
The measurement steps are as follows:
the method comprises the following steps: and measuring the nonlinear signal of the substrate by using a Z scanning device, changing the energy of incident laser, observing the transmission signal of the substrate under different energies, and calibrating the energy (energy A) corresponding to the nonlinear signal when the substrate begins to show. When the incident energy is lower than the energy A, no nonlinear signal is generated by the substrate.
Step two: and measuring the nonlinear signal of the film sample by using a Z scanning device, changing the energy of incident laser, observing the transmission signal of the film sample under different energies, and calibrating that the nonlinear signal of the film material obviously appears in a certain energy range (energy B1-energy B2).
Step three: comparing the energy B2 with the energy A, if the energy B2 is less than the energy A, it means that the nonlinear response of the substrate is nearly zero during the testing process of the film sample, and the influence can be directly ignored, and the nonlinear signal of the film material is directly obtained in the second step.
Step four: if energy B2 is greater than or equal to energy A, it indicates that a non-linear response of the substrate has occurred during testing of the film sample. Because the material with ultra-thin thickness and ultra-low nonlinear optical coefficient is used as the substrate of the film, the nonlinear signal of the film material still dominates the total signal of the film and the substrate, and the influence of the substrate can be eliminated by applying the double-arm Z-scanning technology, and the nonlinear signal corresponding to the film material can be obtained.
Step five: fitting the nonlinear absorption signal of the film by using a formula (1) to obtain a two-photon absorption coefficient beta; fitting the film nonlinear refraction signal by using a formula (2) to obtain a nonlinear refractive index coefficient n2：
Wherein I00Is the laser energy density at the focal point, LeffIs the effective thickness of the film, z0Is a confocal parameter.
Compared with the prior art, the invention has the following beneficial effects:
by selecting the material with ultra-thin thickness and ultra-low nonlinear optical coefficient as the substrate of the thin film element, the nonlinear response of the substrate is very small or even negligible in the double-arm Z-scanning experimental process, so that the influence of the nonlinear effect of the substrate on the measurement of the nonlinear coefficient of the thin film material is inhibited, and the purpose of improving the measurement precision is realized.
Drawings
FIG. 1 is a schematic view of a substrate and a thin film material
FIG. 2 is a schematic diagram of dual arm Z-scan
FIG. 3 shows an incident energy of 1.8. mu.J, 50. mu. mMgF2Blank substrate normalized transmittance profile
FIG. 4 is a graph of incident energy of 1.3 μ J, 200nmSiO2Normalized transmittance curve chart of film material
Detailed Description
The following detailed description of specific embodiments of the invention is made with reference to the accompanying drawings.
In this embodiment, the substrate material is 50 μm MgF2The substrate is made of SiO2. Applying electron beam evaporation technology to evaporate 200nmSiO2Coating the film on 50 mu mMgF2On a substrate as shown in fig. 1.
The nonlinear optical coefficient of the thin film material is measured by using the Z-scan technique, and FIG. 2 is a schematic diagram of a double-arm Z-scan apparatus. The incident laser is femtosecond pulse laser with wavelength of 515nm, pulse width of 230fs, pulse repetition frequency of 1kHz, beam waist radius of 4mm before focusing, and convex lens focal length of 150 mm.
The following measurement of 200nmSiO is made by taking the two-photon coefficient measurement of the thin film material as an example2Nonlinear signal of the film:
1. determination of 50. mu. mMgF2The energy range of the blank substrate where the nonlinear absorption effect occurs is shown in fig. 3, and when the incident single pulse energy is 1.8 muj, the normalized transmittance of the substrate material is approximately a straight line. Therefore, it can be determined that when the incident energy is < 1.8 μ J, the substrate material is substantially free of nonlinear signals, and its effect on the thin-film material measurement can be ignored.
2. Measurement of 200nmSiO2Nonlinear signal of film sample. The normalized transmittance curve is shown in FIG. 4 when the incident energy is 1.3 μ J.
3. Since the energy tested in step 2 is much smaller than the energy range of the nonlinear response generated by the substrate, the influence of the substrate can be ignored at the energy, and the nonlinear signal of the thin film material is directly obtained, i.e. as shown in fig. 4.
4. Using formulas
(LeffIs the effective thickness of the film, z0As confocal parameter) when the energy density I is00Is 1.64X 103GW/cm2Then fitting to obtain SiO2The two-photon absorption coefficient of the film was 1.64 cm/GW.
The invention has important significance for measuring the nonlinear coefficient of the thin-film material and is beneficial to promoting the application of the thin-film material in the field of nonlinear optics.
The above description is only exemplary of the present invention and should not be taken as limiting the invention, as any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (4)
1. A method for improving the measurement accuracy of the nonlinear optical coefficient of a thin-film material is characterized by comprising the following steps:
step 1. selection of the substrate of the thin-film element: the thickness of the substrate is less than or equal to 0.1mm, and the nonlinear optical coefficient of the substrate is less than that of the film material;
step 2, measuring nonlinear signals of a thin film element containing a substrate and a bare substrate by a double-arm Z scanning technology, specifically:
step 2.1, measuring a nonlinear signal of the substrate by using a Z scanning device, changing the energy of incident laser, observing transmission signals of the substrate under different energies, calibrating the energy, namely the energy A, corresponding to the nonlinear signal when the substrate begins to show, and when the incident energy is lower than the energy A, generating no nonlinear signal on the substrate;
step 2.2, measuring the nonlinear signal of the film sample by using a Z scanning device, changing the energy of incident laser, observing the transmission signal of the film sample under different energies, and calibrating the transmission signal within a certain energy range, namely energy B1-energy B2, wherein the nonlinear signal of the film material obviously appears;
step 2.3, comparing the energy B2 with the energy A:
if the energy B2 is less than the energy A, it indicates that the nonlinear response of the substrate is approximately zero during the testing of the film sample, i.e. step 2.2 obtains a nonlinear signal of the film material;
if the energy B2 is greater than or equal to the energy A, it indicates that the nonlinear response of the substrate has been generated during the testing process of the film sample, and the influence of the substrate is eliminated by applying the double-arm Z-scan technique to obtain the nonlinear signal corresponding to the film material;
step 2.4, fitting the nonlinear absorption signal of the film by using the formula (1) to obtain a two-photon absorption coefficient beta; fitting the film nonlinear refraction signal by using a formula (2) to obtain a nonlinear refractive index coefficient n2：
Wherein I00Is the laser energy density at the focal point, LeffIs the effective thickness of the film, z0Is a confocal parameter.
2. The method for improving the measurement accuracy of the nonlinear optical coefficient of the thin film material as claimed in claim 1, wherein the substrates of the two arms have the same thickness and optical constants during the two-arm Z-scan test.
3. The method for improving the measurement accuracy of the nonlinear optical coefficient of the thin-film material as claimed in claim 1 or 2, wherein the substrate material is MgF2Or GaF2。
4. The method for improving the measurement accuracy of the nonlinear optical coefficient of the thin-film material as claimed in claim 1 or 2, wherein the thin-film material is ZnSe, ZnO or HfO2、SiO2Or Al2O3。
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Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
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| JPS5839933A (en) * | 1981-09-02 | 1983-03-08 | Mitsubishi Electric Corp | Inspection method of packaging printed circuit substrate |
| CN105092477A (en) * | 2015-08-26 | 2015-11-25 | 中国工程物理研究院激光聚变研究中心 | Optical nonlinearity measuring device and measuring method for nonlinearity thick photonics materials |
| CN107192670A (en) * | 2017-05-03 | 2017-09-22 | 中国科学院上海光学精密机械研究所 | The measurement apparatus and measuring method of material linear absorption and non-linear absorption |
| CN111024676A (en) * | 2020-01-10 | 2020-04-17 | 河南工程学院 | Novel nonlinear Z-scan measuring method and device |
| CN210487598U (en) * | 2019-08-21 | 2020-05-08 | 苏州微纳激光光子技术有限公司 | Z scanning optical nonlinear measurement all-in-one machine |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
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| US20050270633A1 (en) * | 2004-05-14 | 2005-12-08 | Peter Herman | Photonic crystal mirrors for high-resolving power fabry perots |
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Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5839933A (en) * | 1981-09-02 | 1983-03-08 | Mitsubishi Electric Corp | Inspection method of packaging printed circuit substrate |
| CN105092477A (en) * | 2015-08-26 | 2015-11-25 | 中国工程物理研究院激光聚变研究中心 | Optical nonlinearity measuring device and measuring method for nonlinearity thick photonics materials |
| CN107192670A (en) * | 2017-05-03 | 2017-09-22 | 中国科学院上海光学精密机械研究所 | The measurement apparatus and measuring method of material linear absorption and non-linear absorption |
| CN210487598U (en) * | 2019-08-21 | 2020-05-08 | 苏州微纳激光光子技术有限公司 | Z scanning optical nonlinear measurement all-in-one machine |
| CN111024676A (en) * | 2020-01-10 | 2020-04-17 | 河南工程学院 | Novel nonlinear Z-scan measuring method and device |
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