CN106338840A - Surface wave field enhancement tunable total internal reflection optical excitation device - Google Patents

Abstract

The invention belongs to the technical field of guided wave optics and optical measurement, in particular to a surface wave field enhanced and tunable total internal reflection optical excitation device. The invention includes a precision lifting platform, an inverted trapezoidal prism, a collimated excitation beam, an ultra-thin flat object-carrying glass and an optical and spectral measurement system; a certain air gap is maintained between the inverted trapezoidal prism and the ultra-thin flat object-bearing glass, and the sample to be measured and the A certain air gap is maintained between the optical and spectral measurement systems; when the incident angle is greater than the internal total reflection angle on the upper surface of the inverted trapezoidal prism, different incident angles are selected to excite the horizontal guided wave mode in the ultra-thin plane object glass, using The surface evanescent wave field formed on the upper surface of the guided wave is used for optical excitation of the sample to be tested, and the distance between the inverted trapezoidal prism and the ultra-thin plane object glass can be strictly controlled by a precision lifting platform, which can realize the ultra-thin plane object glass Continuous modulation of field enhancement of evanescent waves on a surface. The invention has important applications in the measurement of fluorescence spectrum, absorption spectrum and Raman spectrum of micro-nano materials.

Description

A tunable total internal reflection optical excitation device with surface wave field enhancement

technical field

The invention belongs to the technical field of guided wave optics and optical measurement, and in particular relates to a surface wave field enhanced and tunable total internal reflection optical excitation device.

Background technique

Total internal reflection fluorescence (TIRF) and surface-enhanced Raman spectroscopy are two effective methods for studying the structure of surface/interface materials. They both use surface evanescent waves to excite molecules shallowly, and There will be no excitation effect on a large number of molecules in the target object, so that selective measurement and analysis can be realized. However, the intensity of the evanescent wave generated by directly using the surface of the high-refractive-index prism is very weak, and generally can only reach the intensity of the incident light. For this reason, to obtain higher intensity evanescent waves, only increase the incident light intensity. For systems that use lasers as light sources, the increase in light intensity is very limited, not to mention the use of incoherent light sources.

The present invention proposes a surface wave field enhanced and tunable total internal reflection optical excitation device, which uses the surface evanescent wave generated by the planar optical waveguide instead of directly using the surface of the prism, and its intensity can be improved compared with the intensity of the incident light source itself 1-3 orders of magnitude, and this enhancement can achieve continuous regulation. The surface evanescent wave intensity of the planar optical waveguide is mainly restricted by the adjustment accuracy of the coupling angle (synchronization angle for short) of the guided wave mode in the planar optical waveguide. The more precisely the synchronization angle is controlled, the stronger the surface evanescent wave is, but the higher its sensitivity to angular misalignment is. In order to overcome this problem, we propose to adjust the coupling distance between the prism and the planar optical waveguide to realize the continuous adjustment of the surface evanescent wave field enhancement under the condition of limited adjustment accuracy of the incident angle.

The advantage of the present invention is that the existing displacement adjustment mechanism with nanometer precision is used to compensate for the high requirements on the angle control accuracy, so that the field strength of the surface evanescent wave can be adjusted under the existing angle control accuracy. Make effective adjustments. At the same time, the evanescent wave intensity adjustment method of the present invention does not involve changing the polarization state of the incident light, so there is no need to install expensive polarizers in the system (especially for mid-to-far infrared bands).

Contents of the invention

The object of the present invention is to provide a total internal reflection optical excitation device capable of effectively adjusting the field strength of surface evanescent waves.

The intensity of the surface evanescent wave generated directly on the surface of the prism by using the principle of total reflection of light is usually equivalent to the intensity of the light incident on the bottom surface of the prism, and the intensity of the surface evanescent wave generated by using the guided wave mode in the planar optical waveguide can reach The enhancement of the light field with a much higher incident light field can reach several orders of magnitude. However, the surface evanescent wave intensity of the planar optical waveguide is very sensitive to the misalignment of the coupling synchronization angle of the waveguide mode, so that the purpose of adjusting the intensity of the evanescent wave cannot be achieved by adjusting the synchronization angle.

In the structure of the prism-coupled planar optical waveguide, for the optical waveguide wave mode excited by a finite precision synchronization angle, the evanescent wave intensity has a relatively slow relationship with the coupling distance between the prism and the planar optical waveguide, which can be changed by changing The method of the coupling spacing realizes the purpose of continuously controlling the surface evanescent wave intensity of the planar optical waveguide under the condition of existing angle control accuracy.

Based on the above principles, the present invention designs a tunable total internal reflection optical excitation device with surface wave field enhancement. Using a nanometer-precision displacement adjustment mechanism, the tuning amount of surface wave field enhancement can reach 2 orders of magnitude. Its structure is shown in Figure 1, which specifically includes: a precision lifting platform, an inverted trapezoidal prism, a collimated excitation beam, an ultra-thin plane object glass, and a set of optical and spectral measurement systems; among them, the inverted trapezoidal prism It is fixed on the above-mentioned precision lifting platform, and the bottom edge of the prism is kept horizontal; above the inverted trapezoidal prism, there are ultra-thin flat object glass, optical and spectral measurement systems in sequence, and a certain distance is maintained between the inverted trapezoidal prism and the ultra-thin flat object glass. Air gap, the ultra-thin plane object glass is used to place the sample to be measured, and a certain air gap is maintained between the sample to be measured and the optical and spectral measurement system; the collimated incident beam is aimed at the inverted trapezoidal prism, which is opposite to the upper The internal incident angle θ of the bottom edge (relative to the normal N of the upper surface of the prism) is greater than the critical angle for total internal reflection; and the incident angle θ can be adjusted continuously; the internally reflected light beam is collected by the reflective light collector.

In the present invention, the precision lifting platform is used to control the distance between the inverted trapezoidal prism and the ultra-thin plane object-carrying glass, which can realize the continuous adjustment of the field enhancement of the evanescent wave on the upper surface of the ultra-thin plane object-carrying glass, and the precise lifting The positioning accuracy of the platform can reach the nanometer level, and the total stroke is not less than 500 nanometers.

In the present invention, the inverted trapezoidal prism is glass with relatively high refractive index (greater than 1.7), such as heavy flint glass.

In the present invention, the collimated incident light beam is a collimated light beam, which is a parallel collimated light beam, and its internal incident angle θ (relative to the normal line N on the upper surface of the prism) for the upper base of the above-mentioned inverted trapezoidal prism will be greater than The critical angle at which total internal reflection occurs. And the incident angle θ can be adjusted continuously, and the adjustment accuracy reaches the second level.

In the present invention, the ultra-thin plane object glass is a flat glass with a thickness not exceeding 50 microns, transparent to the wavelength band of the collimated excitation beam, and having a refractive index not exceeding that of an inverted trapezoidal prism. The ultra-thin plane object glass acts as a plane light waveguide in operation, and is used to generate surface evanescent waves on its upper surface, and its spatial position is relatively fixed in the whole device.

In the present invention, a certain air gap should be maintained in the inverted trapezoidal prism and the ultra-thin flat object-mounting glass, that is, the inverted trapezoidal prism and the ultra-thin flat object-mounting glass are not connected to each other, and there is a layer of air gap between them, which can be passed through the above precision The lifting platform is adjusted.

In the present invention, a certain air gap is maintained between the sample to be measured and the optical and spectral measurement system, that is, a certain air gap must be maintained between the sample to be measured and the light collection unit (such as a microscopic objective lens) in the optical and spectral measurement system. The air gap cannot be infiltrated with oil, and the spacing is generally not less than 1 micron.

In the present invention, the optical and spectral measurement system includes a photoelectric conversion mechanism for light intensity measurement and a spectral measurement mechanism for measuring fluorescence spectrum, absorption spectrum and Raman spectrum, as well as related data collection and processing.

In the present invention, when the incident angle is greater than the internal total reflection angle on the upper surface of the inverted trapezoidal prism, different incident angles are selected to excite the horizontal guided wave mode in the ultra-thin flat object-bearing glass, and the guided wave is used to form a The surface evanescent wave field of the sample to be tested is optically excited, and the distance between the inverted trapezoidal prism and the ultra-thin flat object glass is strictly controlled by a precision lifting platform, which can realize the field of the evanescent wave on the upper surface of the ultra-thin flat object glass. Enhanced continuous adjustment, the amount of adjustment can reach 2 orders of magnitude, which is related to the selected waveguide mode and the accuracy of the incident beam angle control mechanism. The device of the present invention can be used in the fluorescence spectrum, absorption spectrum and It has important applications in Raman spectroscopy and other aspects.

Advantage of the present invention:

1. It is to use the existing displacement adjustment mechanism with nanometer precision to make up for the excessive requirements on the angle control accuracy. Therefore, in the case of the existing angle control accuracy, the field strength of the surface evanescent wave can be effectively adjusted;

2. For the instrument system that has been equipped with a nano-displacement control mechanism in the existing measurement system, the present invention can simply add an ultra-thin plane object glass to realize the original total internal reflection on the surface of the prism. The magnitude of the generated surface evanescent wave field is enhanced, and with this enhancement can be continuously tuned. Therefore, effective functional upgrades can be carried out on existing instruments and equipment;

3. The evanescent wave intensity adjustment method of the present invention does not involve the change of the polarization state of the incident light, so there is no need to install an expensive polarizer in the system, especially for the mid-to-far infrared band, the polarizer and its adjustment mechanism are very expensive of. Therefore, it helps to reduce the system cost.

Description of drawings

Fig. 1 is a schematic diagram of a surface wave field enhanced tunable total internal reflection optical excitation device.

Figure 2 shows the spatial variation of the surface evanescent field intensity. Among them, (1) the left Y axis (prismatic data point) is the evanescent wave generated by the surface of the prism coupling planar light guide, (2) the right Y axis (linear data) is the evanescent wave generated only by the total internal reflection of the prism on the surface For evanescent waves, the incident angle inside the prism is 38.3594° in both cases.

Fig. 3 shows how the intensity ratio of the evanescent wave maximum on the prism-coupled planar waveguide surface to the evanescent wave maximum generated only on the prism surface varies with the coupling distance between the prism and the planar waveguide. Among them, the incident angle inside the prism is 38.3594° (accuracy is the 4th place after the decimal point), and the 3 curves represent the change of the incident angle at the 5th place after the decimal point.

Numbers in the figure: 1 is the precision lifting platform, 2 is the collimated excitation beam, 3 is the inverted trapezoidal prism, 5 is the ultra-thin plane object glass, 4 is the air gap between the inverted trapezoidal prism and the ultra-thin plane object glass, 6 is the reflected light collector, 7 is the measurement sample, 9 is the optical and spectral measurement system, 8 is the air gap between the sample to be measured and the optical and spectral measurement system.

detailed description

The surface wave field enhanced and tunable total internal reflection optical excitation device designed by the present invention specifically includes: a precision lifting platform, an inverted trapezoidal prism, a collimated excitation beam that undergoes total internal reflection, and an ultra-thin flat object-bearing glass , a certain air gap should be maintained between the inverted trapezoidal prism and the ultra-thin plane object glass, and a set of optical and spectral measurement systems, and a certain air gap should be maintained between the sample to be measured and the optical and spectral measurement system. When the incident angle is greater than the internal total reflection angle on the upper surface of the inverted trapezoidal prism, different incident angles are selected to excite the horizontal guided wave mode in the ultra-thin planar object glass, and the surface evanescence formed by the guided wave on its upper surface is used The wavefield performs optical excitation on the sample to be tested. Strictly control the distance between the inverted trapezoidal prism and the ultra-thin plane object glass by using a precision lifting platform, which can realize the continuous adjustment of the field enhancement of the evanescent wave on the upper surface of the ultra-thin plane object glass, and the adjustment amount can generally reach 2 An order of magnitude is related to the selected waveguide mode and the accuracy of the incident beam angle adjustment mechanism adopted. The device of the present invention can be used in the measurement of fluorescence spectrum, absorption spectrum, and Raman spectrum of micro-nano materials. The schematic diagram of the structure is shown in Figure 1.

According to the structure shown in Figure 1, select a laser working wavelength such as: 632.8nm, the material of the inverted trapezoidal prism is selected heavy flint glass, the refractive index is 1.85, and the ultra-thin plane object glass is taken as flint glass, the refractive index is 1.60, the thickness is 40 microns. The air gap between the inverted trapezoidal prism and the ultra-thin flat object glass was initially set to 0.5 μm.

A collimated light beam is incident on the bottom edge of the inverted trapezoidal prism according to the optical path shown in Figure 1. When the critical angle of total internal reflection is greater than the critical angle of total internal reflection, the incident light will be excited inside the ultra-thin plane object glass after passing through the inverted trapezoidal prism. Many guided wave modes can be selected from which the corresponding guided wave can be selected by adjusting the incident angle of the incident light. Assuming that the incident light intensity on the upper and lower edges inside the prism is 1, taking the transverse electric wave (TE wave) as an example, the incident light is inside the prism, the air gap, and the light field of each part inside and on the surface of the ultra-thin plane object glass The field strength expressions of can be written out using the strict coupled wave theory, and quantitatively calculated according to the continuity condition of the TE wave electric field vector at the boundary. Similarly, the surface evanescent field formed only by the total internal reflection on the surface of the prism can also be calculated with the corresponding theory. The relevant calculation results are shown in Figure 2 and Figure 3 .

Figure 2 shows the spatial variation of the intensity of the evanescent field on the surface of the prism-coupled planar optical waveguide (prismatic data, left Y-axis), and the evanescent field on the surface of the prism alone for an incident angle of 38.3594° inside the prism in the structure shown in Figure 1 Spatial variation of field intensity (linear data, right y-axis). It can be seen from the data in the figure that the surface evanescent field intensity (Y axis on the left) generated by the prism coupled with the planar optical waveguide is the strongest on the glass surface, and its value is 1495.63 at the above incident angle. At this time, the prism and the glass planar waveguide The coupling pitch is 0.5 µm. In the case of the same incident angle, the intensity of the evanescent wave generated only by total internal reflection on the surface of the prism (right Y axis) is only 3.47. It can be seen that the surface evanescent wave generated on the surface of the planar optical waveguide after being coupled by the prism is at least 2 orders of magnitude stronger than the evanescent wave generated only by the total internal reflection of the prism.

At this time, when the incident angle of the collimated light in the fixed prism remains unchanged, changing the coupling distance between the prism and the glass planar waveguide can change the intensity of the evanescent field on the surface of the glass planar waveguide. Figure 3 shows the related results. The coupling pitch varies from 0.1 micron to 0.9 micron. It can be seen that the ratio of the intensity of the evanescent field at the surface of the glass planar waveguide to the intensity of the evanescent wave generated only by the surface of the prism varies continuously from about 3.1, through a peak of 610, to about 4.4. That is, the increment of evanescent wave intensity can reach 610, which is greater than two orders of magnitude. However, the maximum value of this increment is related to the control accuracy of the incident angle of light in the prism. When the fifth digit of the incident angle changes, the maximum value of the increment, as shown in Figure 3, is 455.5 and 513.4 respectively. , and 610.

At the same time, it should be noted that, as can be seen from Figure 3, the rate of change of the adjustment of the coupling spacing to the evanescent wave intensity on both sides of the center is also related to the accuracy of the incident angle. The left half of the center, that is, the coupling spacing is from 0.5 to 0.1 microns, the coincidence of the three curves is very good, while the right half, that is, from 0.5 to 0.9 microns, relatively speaking, the coincidence of the three precision curves is relatively poor. Therefore, for the intensity control of the surface evanescent wave generated by the planar waveguide, it is advisable to use the left half of the center of the coupling spacing variation, so that the influence of the angle control accuracy will be minimal.

The above results are achieved with incident angle precision controlled to the 4th decimal place. The angle control accuracy of the current mechanical turntable can reach about 1 second, that is, the fourth digit after the decimal point, which can basically meet the above-mentioned purpose of controlling the evanescent wave intensity. If a more precise rotating mechanism is used to control the incident angle, the relative field enhancement will be further increased.

Claims (8)

1. A surface wave field enhanced tunable total internal reflection optical excitation device is characterized in that it includes: a precision lifting platform, an inverted trapezoidal prism, a bunch of collimated excitation light beams, an ultra-thin plane object glass, and A set of optical and spectral measurement system; wherein, the inverted trapezoidal prism is fixed on the above-mentioned precision lifting platform, and the bottom edge of the prism is kept horizontal; above the inverted trapezoidal prism is an ultra-thin flat object glass, optical and spectral measurement system, inverted trapezoidal There is a certain air gap between the prism and the ultra-thin plane object glass. The ultra-thin plane object glass is used to place the sample to be measured. There is a certain air gap between the sample to be measured and the optical and spectral measurement system; the incident beam is collimated Aligning the inverted trapezoidal prism, its internal incident angle θ to the upper base of the inverted trapezoidal prism is greater than its critical angle for total internal reflection; and the incident angle θ can be continuously adjusted; the internally reflected light beam is collected by a reflective light collector. 2. The surface wave field enhanced tunable total internal reflection optical excitation device according to claim 1, wherein the precision lifting platform is used to control the distance between the inverted trapezoidal prism and the ultra-thin plane object glass to realize The continuous adjustment of the field enhancement of the evanescent wave on the upper surface of the ultra-thin plane object glass, the positioning accuracy of the precision lifting platform reaches the nanometer level, and the total stroke is not less than 500 nanometers. 3 . The surface wave field enhanced tunable total internal reflection optical excitation device according to claim 1 , wherein the inverted trapezoidal prism is glass with a refractive index greater than 1.7. 4 . 4 . The surface wave field enhanced tunable total internal reflection optical excitation device according to claim 1 , wherein the collimated incident light beam is a parallel collimated light beam, and the adjustment accuracy of the incident angle θ reaches the second level. 5. The surface wave field enhanced tunable total internal reflection optical excitation device according to claim 1, wherein the ultra-thin plane object glass is a flat glass with a thickness of no more than 50 microns, and aligned The wavelength band where the excitation beam is located is transparent, and its refractive index does not exceed that of the inverted trapezoidal prism. 6. The surface wave field enhanced tunable total internal reflection optical excitation device according to claim 1, characterized in that, the ultra-thin plane object-carrying glass plays the role of a planar light waveguide in operation, and is used for Surface evanescent waves are generated, whose spatial position is relatively fixed throughout the device. 7. The surface wave field enhanced tunable total internal reflection optical excitation device according to claim 1, characterized in that the air gap between the sample to be measured and the optical and spectral measurement system is not less than 1 micron. 8. The surface wave field enhanced tunable total internal reflection optical excitation device according to claim 1, wherein the optical and spectral measurement system includes a photoelectric conversion mechanism for light intensity measurement, and a spectral measurement mechanism, using It is used for the measurement of fluorescence spectrum, absorption spectrum and Raman spectrum, as well as related data collection and processing.