A wide-band phase object, 4f optical nonlinear measurement system and measurement method

Abstract

The present application proposes a wide-band phase object, a 4f optical nonlinear measurement system and a measurement method. The phase object uses two glass slides to overlap to produce a gap to meet the basic requirements for making a phase object, and is made into an ordinary phase object and an absorptive phase object, which is placed on a rotating platform. The thickness of the phase object is controlled by adjusting the rotation angle of the rotating platform to achieve the control of the phase of the phase object. When the phase produced by the phase object is an integer multiple of π / 2, complete interference bright or dark lines will appear on the central liquid film or film, and the nonlinear refraction phenomenon of the sample to be measured can be clearly observed, and the optimal sensitivity can be achieved at this time. Another use of fixing the phase object on the rotating platform is that the thickness of the phase object can be freely and accurately controlled. Under continuous wavelength waves, the appropriate thickness at the corresponding wavelength can be found by adjusting the rotation angle of the rotating platform to achieve the optimal measurement sensitivity.

Description

Technical Field

[0001] The present application relates to the technical field of optical nonlinear measurement, and in particular to a wide-band phase object, system and measurement method for measuring nonlinear effects. Background Art

[0002] With the increasing development of nonlinear optics, a large number of materials with optical nonlinear properties have been discovered and applied to optoelectronic devices, optical information processing, optical communications, etc. In order to find optical nonlinear materials for various purposes, a large number of techniques for measuring optical nonlinear materials have been proposed for screening ideal nonlinear materials. However, for the study of some materials with relatively weak optical nonlinear properties, some highly sensitive technical methods are needed to measure the materials. 4f coherent imaging technology (Sudhir Cherukulappurath, Georges Boudebs, and Andre Monteil, "4f coherentimager system and its application to nonlinear optical measurements" Opt. Soc. Am. B 21, 273 (2004)) is a commonly used technology for measuring optical nonlinear related physical parameters. This method mainly uses the beam distortion method. This technology does not require moving the sample, has low requirements for the spatial distribution of the light spot, and relies on the spatial distribution of the nonlinear light spot to detect the sample. However, when this method was applied in the early stage, it was unable to distinguish the sign of the optical nonlinear refraction of the material.

[0003] In 2004, G. Boudebs et al. introduced a 4f phase coherent imaging technology using a phase object for optical nonlinear measurement on the incident surface of the 4f system (G. Boudebs and S. Cherukulappurath, "Nonlinearoptical measurements using a 4f coherent imaging systemwith phase objects", PHYSICAL REVIEW A 69, 053813 (2004)). The improved 4f system adds an important device, the phase object. This technology uses the phase contrast principle to convert the phase change of the phase object passing through the nonlinear sample into the intensity change of light, measures the optical nonlinear related physical parameters of the sample, and solves the sign problem of nonlinear refraction. Since then, it has been widely used to measure the optical nonlinear properties of materials.

[0004] As the application of this technology becomes more and more widespread, the research and preparation of phase objects quickly enters people's field of vision. The principle of realizing phase objects (PO) is that when the thickness of an object changes, its phase also changes, so the thickness control of the phase object becomes particularly important. There are currently three methods for realizing phase objects:

[0005] (1) Using a piezoelectric ceramic displacement platform, but the piezoelectric ceramic displacement platform is not only expensive, but also has a minimum step distance limit and a complex manufacturing process;

[0006] (2) Fixed thickness phase object, but fixed thickness phase object is only for fixed wavelength, can not achieve the optimal measurement sensitivity under continuous wavelength, and there are errors in the process of realizing phase object. (3) Use spatial light modulator to realize phase modulation of light, but this method requires expensive spatial light modulator. Summary of the invention

[0007] In order to solve the above problems, the present application proposes a method for measuring a wide-band phase object with nonlinear effect, which has good phase controllability and high measurement sensitivity.

[0008] To achieve the above objectives, this application adopts the following technical solutions:

[0009] A wide-band phase object, used for measuring nonlinear effects of a sample to be measured, characterized by comprising:

[0010] The first slide and the second slide,

[0011] The first glass slide and the second glass slide are stacked with a gap therebetween, a liquid film is in the gap, and the first glass slide and the second glass slide are made of transparent glass.

[0012] Preferably, the thickness of the liquid film is between 0.5 μm and 1 mm.

[0013] The embodiment of the present application provides a 4f optical nonlinear measurement system, comprising: an incident laser beam, wherein the incident laser beam optical path is provided with: a reflector, the above-mentioned wide-band phase object, a first convex lens, a sample to be measured, a second convex lens, and a CCD in sequence;

[0014] The wide-band phase object is fixed on a rotating device, and the wide-band phase object is placed on the object plane of the incident surface of the system; the rotating axis of the rotating device is perpendicular to the optical axis;

[0015] The image focus of the first lens coincides with the object focus of the second lens. The sample to be tested is placed at the image focus of the first lens, that is, the sample to be tested is placed on the Fourier plane of the system, and the CCD is placed on the image plane of the system output surface.

[0016] The incident light emitted by the incident laser beam is reflected by the reflector and enters the wide-band phase object. It is Fourier transformed by the first lens and reaches the front surface of the sample on the Fourier plane. The light spot is filtered by the nonlinear sample to be tested and then emitted from the rear surface of the sample to be tested. It is Fourier inverse transformed by the second lens to collect the light spot.

[0017] The CCD is used to obtain the light spot image passed through the second lens.

[0018] Preferably, in the 4f optical nonlinear measurement system, the rotating device is rotated to adjust the thickness of the broadband phase object.

[0019] The expression is: In the formula, is the phase generated by the wide-band phase object, d is the liquid film thickness, λ is the wavelength of the incident laser beam, and θ is the rotation angle of the rotating stage.

[0020] Preferably, the rotating device comprises: a spectrometer, a dividing plate and a CNC turntable.

[0021] The present application embodiment provides an optical nonlinear measurement method using the above system, the method comprising:

[0022] The attenuation sheet is placed in front of the sample to be tested, and the first image after passing through the sample to be tested is received by using the CCD;

[0023] The same attenuation sheet is placed behind the sample to be tested, the rotating device is adjusted to control the phase of the wide-band phase object, and the second image after passing through the sample to be tested is received by the CCD;

[0024] The obtained first image and second image are processed to obtain the optical nonlinear parameters of the sample to be tested.

[0025] Preferably, the second image, wherein the second light spot is the brightest interference fringe or the darkest interference fringe, is a nonlinear image.

[0026] Preferably, the first image is a linear image.

[0027] Preferably, in the optical nonlinear measurement method,

[0028] Processing the obtained first image and the second image includes: placing the nonlinear curve and the linear curve in the same chart to obtain nonlinear parameters.

[0029] Beneficial Effects

[0030] The implementation methods of the present application have good phase controllability and form a complete phase cycle; there is no wavelength limitation and the device manufacturing is flexible and changeable; the optimal measurement sensitivity can be achieved under continuous wavelengths and the absorption phase object can be manufactured to improve the measurement sensitivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 A schematic diagram of a wide-band phase object according to an embodiment of the present application;

[0032] Figure 2 A schematic diagram of a wideband phase object and a rotating device according to an embodiment of the present application;

[0033] Figure 3 This is a schematic diagram of a 4f optical nonlinear measurement system according to an embodiment of the present application;

[0034] Figure 4 (a), (b), and (c) are linear images obtained through image processing in this application;

[0035] Figure 5 (a), (b), and (c) are nonlinear images obtained through image processing in the present application;

[0036] Wherein: 1. incident laser beam; 2. reflector; 3. wide-band phase object; 4. first convex lens; 5. sample to be measured; 6. second convex lens; 7. CCD. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solutions and advantages of the present application clearer, the present application will be further described in detail with reference to the accompanying drawings. In the following, the terms "first", "second", etc. are used for descriptive purposes only and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features. Therefore, the features defined as "first" or "second" may explicitly or implicitly include one or more of the features.

[0038] Embodiment 1

[0039] like Figure 1 As shown, a wide-band phase object is used to measure the nonlinear effect of a sample to be measured, characterized by comprising: a first glass slide 10 and a second glass slide 20, the first glass slide and the second glass slide are stacked with a gap between them, a liquid film 30 is present in the gap, the first glass slide and the second glass slide are transparent glass, and the thickness of the liquid film is 0.5 μm-1 mm.

[0040] The phase object in this application uses two glass slides to overlap to create a gap to meet the basic requirements for making a phase object, such as Figure 2 As shown, a wide-band phase object 3 is made and placed on a rotating device 40. Figure 2The thickness of the phase object is controlled by the rotating device 40 (as shown by the arrow in the middle), thereby controlling the phase of the wide-band phase object. When the wide-band phase object produces a phase that is an integer multiple of π / 2, complete interference bright or dark fringes will appear on the central liquid film or film, and the nonlinear refraction phenomenon of the sample to be measured can be clearly observed. At this time, the optimal sensitivity can be achieved. Another use of fixing the wide-band phase object on the rotating device 40 is that the thickness of the phase object can be freely and accurately controlled. Under continuous wavelength waves, the appropriate thickness under the corresponding wavelength can be found by adjusting the rotation angle of the rotating device to achieve the optimal measurement sensitivity.

[0041] When the wideband phase object is produced,

[0042] First, drop a colorless transparent liquid on the first slide glass 10.

[0043] Then the first glass slide 20 is overlapped and squeezed to form a liquid film 30. The size of the liquid film after squeezing should be less than or equal to about 0.5μm. During measurement (using the 4f system), the prepared wide-band phase object 3 is fixed and placed on a rotating table. The thickness change of the phase object is achieved by using the rotation angle of the rotating table.

[0044] The expression is In the formula, is the phase produced by the phase object, d is the water film thickness (colored liquid film or film thickness), λ is the wavelength of the light source, and θ is the rotation angle of the rotating stage.

[0045] Embodiment 2

[0046] A 4f optical nonlinear measurement system, the system having 4f imaging, such as Figure 3 The device includes: an incident laser beam 1, the wavelengths of which are 532, 650, and 800 nm, respectively; the device is characterized in that the incident laser beam optical path is provided with: a reflector 2, a wide-band phase object 3, a first convex lens 4, a sample to be measured 5, a second convex lens 6, and a CCD 7 in sequence;

[0047] The wide-band phase object is fixed on a rotating device, and the wide-band phase object is placed on the object plane of the incident surface of the system; the rotating axis of the rotating device is perpendicular to the optical axis;

[0048] The image focus of the first lens coincides with the object focus of the second lens. The sample to be tested is placed at the image focus of the first lens, that is, the sample to be tested is placed on the Fourier plane of the system, and the CCD is placed on the image plane of the system output surface.

[0049] The incident light emitted by the incident laser beam is reflected by the reflector and enters the wide-band phase object. It is Fourier transformed by the first lens and reaches the front surface of the sample on the Fourier plane. The light spot is filtered by the nonlinear sample to be tested and then emitted from the rear surface of the sample to be tested. It is Fourier inverse transformed by the second lens to collect the light spot.

[0050] The CCD is used to obtain the light spot image passed through the second lens.

[0051] The attenuation plate is placed in front of the sample to be tested, and the first image after passing the sample to be tested is received by CCD, and the first image is a linear image; the same attenuation plate is placed behind the sample to be tested, and the rotating device is adjusted to control the phase of the wide-band phase object, and the second image after passing the sample to be tested is received by CCD; the first image and the second image obtained are processed to obtain the optical nonlinear parameters of the sample to be tested; the second image, the second light spot is the brightest interference fringe or the darkest interference fringe, which is a nonlinear image; the nonlinear curve and the linear curve are placed in the same chart to obtain the nonlinear parameters.

[0052] In at least one specific application example, the incident laser beam uses 532nm, 650nm, and 800nm ​​lasers of ytterbium-doped fiber (Yb:KGW) femtosecond lasers with a pulse width of 190fs. The CCD uses ADIMEC-4020m, the sample to be tested uses anhydrous ethanol, and the rotating device uses a spectrometer.

[0053] The optical nonlinear measurement method using the 4f optical nonlinear measurement system of the present application is as follows:

[0054] (1) The sample to be tested is placed at the focus of the first lens, and a sufficiently large high-density neutral attenuation plate is placed in front of the sample to be tested. The CCD receives a linear image of the sample to be tested. The first image captured by the CCD is as follows: Figure 4 As shown, Figure 4 (a), (b), and (c) are linear spots collected by 532nm, 650nm, and 800nm ​​lasers respectively;

[0055] (2) The position of the sample to be tested remains unchanged. After placing the same high-density neutral attenuation plate on the sample to be tested, rotate the spectrometer under the wide-band phase object until complete interference bright fringes appear in the CCD. At this time, the second image of the CCD is as follows: Figure 5 As shown, Figure 5 (a), (b), and (c) are the nonlinear light spots of the sample to be tested collected by 532nm, 650nm, and 800nm ​​lasers respectively;

[0056] (3) Yes Figure 4 (a), (b), (c) Figure 5The images (a), (b), and (c) are processed and compared to obtain a nonlinear curve of the sample to be tested.

[0057] The specific process of the experiment and theoretical calculation for the thickness control of the wide-band phase object and the nonlinear measurement of the sample to be tested is as follows:

[0058] In the 4f system, from the incident surface to the propagation to the lens focus, that is, the Fourier transform on the Fourier surface, the formula is:

[0059]

[0060] Where S(u,v,t) is the electric field reaching the Fourier surface, u and v are the spatial frequencies on the Fourier surface, f1 is the focal length of lens 4, and O(x,y,t) is the electric field passing through the phase object on the incident surface. After passing through the nonlinear sample, without considering absorption, the electric field distribution on the sample exit surface can be expressed as:

[0061]

[0062] In the formula n2 is the nonlinear refractive index, L is the thickness of the sample to be tested, and I(u,v,t) is the s inside the sample to be tested. L The (u, v, t) light intensity follows the inverse Fourier transform from the Fourier plane to the exit plane of the 4f measurement system. Then the light intensity distribution detected by the CCD can be expressed as:

[0063] I m =|λf1FT -1 [s L (u,v,t)H(u,v)]| 2 (3)

[0064] In the formula, FT -1 is the inverse Fourier transform, and H(u,v) is the optical transfer function. The above formula and experimental data can be used to verify the feasibility of wide-band phase objects and their use at multiple wavelengths.

[0065] This application uses cheap materials and a simple manufacturing process to solve the problems of the original phase object being expensive and complicated. By controlling the thickness of the phase object, the phase of the phase object can be adjusted arbitrarily, and the nonlinear properties of the material can be measured at continuous wavelengths. The optimal measurement sensitivity of the system can be achieved at each wavelength, solving the problem that the original phase object cannot be measured at continuous wavelengths. At the same time, the solution proposed in this application uses a colored liquid film or a thin film to make an absorption-type phase object, thereby improving the measurement sensitivity of the system.

[0066] The above embodiments are only for illustrating the technical concept and features of the present application, and their purpose is to enable people familiar with the technology to understand the content of the present application and implement it accordingly, and they cannot be used to limit the protection scope of the present application. Any equivalent transformation or modification made according to the spirit of the present application shall be included in the protection scope of the present application.

Claims

1. A 4f optical nonlinear measurement system, comprising: An incident laser beam, wherein the following are arranged in sequence on the optical path of the incident laser beam: a reflector, a wide-band phase object, a first convex lens, a sample to be measured, a second convex lens, and a CCD; The broadband phase object comprises: a first glass slide and a second glass slide, wherein the first glass slide and the second glass slide are stacked with a gap therebetween, wherein a liquid film is present in the gap, and the first glass slide and the second glass slide are transparent glass; the thickness of the liquid film is between 0.5 μm and 1 mm; and the characteristics are: The wide-band phase object is fixed on a rotating device, and the wide-band phase object is placed on the object plane of the incident surface of the system; the rotating axis of the rotating device is perpendicular to the optical axis; The image focus of the first lens coincides with the object focus of the second lens. The sample to be tested is placed at the image focus of the first lens, that is, the sample to be tested is placed on the Fourier plane of the system, and the CCD is placed on the image plane of the system output surface. The incident light emitted by the incident laser beam is reflected by the reflector and enters the wide-band phase object, undergoes Fourier transformation through the first lens, and reaches the front surface of the sample on the Fourier plane. The light spot is filtered by the nonlinear sample to be tested, and then emitted from the rear surface of the sample to be tested. The light spot is collected by Fourier inverse transformation through the second lens, and the CCD is used to obtain the light spot image after the second lens. rotating the rotating device to adjust the thickness of the broadband phase object, The expression is: In the formula, is the phase generated by the wide-band phase object, d is the liquid film thickness, λ is the wavelength of the incident laser beam, and θ is the rotation angle of the rotating stage; The rotating device comprises: a spectrometer, a dividing plate and a numerically controlled turntable.

2. An optical nonlinear measurement method using the system of claim 1, characterized in that: The method comprises: The attenuation sheet is placed in front of the sample to be tested, and the first image after passing through the sample to be tested is received by using the CCD; The same attenuation sheet is placed behind the sample to be tested, the rotating device is adjusted to control the phase of the wide-band phase object, and the second image after passing through the sample to be tested is received by the CCD; The obtained first image and second image are processed to obtain the optical nonlinear parameters of the sample to be tested.

Images