CN106768345B - Method based on surface plasma direct measurement vertically polarized light polarization state - Google Patents

Abstract

The invention relates to a method for directly measuring the polarization state of longitudinally polarized light based on surface plasmons. When metal nanoparticles are excited by light, the distribution of surface plasmons generated by the metal nanoparticles is determined by the polarization state of the excitation light. Based on this phenomenon, a detection substrate is designed, and the polarization state of the excitation light can be judged by observing the pattern on the recording layer of the detection substrate after exposure. The direct measurement of the longitudinal polarization state of the longitudinally polarized light is realized, which cannot be realized by other current polarization measurement methods; the measurement method is simple, effective and easy to implement.

Description

A Method for Directly Measuring the Polarization State of Longitudinal Polarized Light Based on Surface Plasmons

technical field

The invention relates to an optical measurement technology, in particular to a method for directly measuring the polarization state of longitudinally polarized light based on surface plasmons.

Background technique

The polarization state of light is one of the important properties of light, and it is a parameter that must be considered in the application and research of light. Therefore, it is particularly important to measure the polarization state of light. For common transversely polarized light, that is, light whose polarization direction is perpendicular to the propagation direction, the polarization direction of the light can be easily determined by rotating the polarizer. But for longitudinally polarized light, that is, light whose polarization direction is the same as the direction of light propagation, the rotation of the polarizer has no effect on the transmission of light, so the polarization state cannot be detected.

At present, there are some indirect methods for measuring the polarization state of longitudinally polarized light: for example, using photoresist to measure the intensity distribution of light on the plane perpendicular to the direction of propagation, using the intensity distribution of the second harmonic, and the method of using dipole scattering. This method requires precise placement of nanoparticles and the use of complex reconstruction algorithms. However, the longitudinally polarized light measured by all these methods has a stronger transverse polarization component than the longitudinal component, and these methods infer the distribution of the longitudinal component electric field through the measurement of the transverse electric field distribution.

Contents of the invention

The present invention aims at the problem that the prior art cannot measure the polarization state of longitudinally polarized light, and proposes a method for directly measuring the polarization state of longitudinally polarized light based on surface plasmons. The state of polarization conundrum.

The technical solution of the present invention is: a method for directly measuring the polarization state of longitudinally polarized light based on surface plasmons, specifically comprising the following steps:

1) Make a detection substrate, which includes a glass substrate, a 200nm-thick chromium thin film recording layer attached to the glass base with the same area as the glass substrate, and metal nanoparticles on the recording layer;

2) Place an adjustable optical power attenuator and an exposure shutter in sequence on the optical path of the beam to be measured, and place a detection substrate at the end of the optical path, that is, the position where the polarization state of the light is measured, with the light incident perpendicularly to the recording layer;

3) Adjust the optical power to the range that meets the measurement requirements through the adjustable optical power attenuator;

4) Adjust the exposure time of the exposure shutter, the light beam to be measured passes through the adjustable optical power attenuator and the exposure shutter, and then is vertically incident on the detection substrate for one exposure;

5) Use a scanning electron microscope to observe the irradiated area of the detection substrate during the exposure process, and record the location of the metal nanoparticles on the recording layer in this area and the surface morphology near it;

6) Obtain the electric field distribution near the position of the metal nanoparticles on the recording layer on the detection substrate through calculation and simulation, and then compare the surface morphology obtained in step 5) with the simulation results to determine the polarization state of the beam to be measured.

The size of the metal nanoparticles on the recording layer is about 1/3 of the wavelength of the measured light beam.

The beneficial effect of the present invention is that: the method for directly measuring the polarization state of longitudinally polarized light based on surface plasmons in the present invention realizes the direct measurement of the longitudinal polarization state of longitudinally polarized light, which cannot be realized by other current polarization measurement methods; the measurement method Simple and effective, easy to implement.

Description of drawings

Fig. 1 is a schematic structural view of a device for directly measuring the polarization state of longitudinally polarized light by surface plasmons of the present invention;

Fig. 2 is the structural representation of detection substrate among the present invention;

Fig. 3 is the electric field distribution diagram near the metal nanoparticles excited by the linearly polarized light obtained by calculation and simulation;

Fig. 4 is the method of the present invention using the present invention, under the excitation of linear polarized light, after exposure, the surface topography of the recording layer at the position of the metal nanoparticles observed by the scanning electron microscope;

Fig. 5 is the electric field distribution diagram near the metal nanoparticles excited by longitudinally polarized light obtained by calculation and simulation;

FIG. 6 is a surface topography diagram of the recording layer at the position of the metal nanoparticles observed by scanning electron microscopy after exposure under the excitation of longitudinally polarized light by using the method of the present invention.

Detailed ways

The basic method of the invention is: when the metal nanoparticles are excited by light, the distribution of surface plasmons generated by the metal nanoparticles is determined by the polarization state of the excitation light. Based on this phenomenon, a detection substrate is designed, and the polarization state of the excitation light can be judged by observing the pattern on the recording layer of the detection substrate after exposure.

Figure 1 is a schematic diagram of the structure of the device for directly measuring the polarization state of longitudinally polarized light based on surface plasmons in the present invention. The light beam to be measured passes through the adjustable optical power attenuator 1 and the exposure shutter 2, and then is vertically incident on the detection substrate 3 . The structural representation of detection substrate as shown in Figure 2, detection substrate 3 comprises bottom glass substrate 31, on glass substrate 31 and the recording layer 32 that the 200 nanometer thick chromium film of the same size area of glass substrate 31 forms, And the metal nanoparticles 33 on the recording layer 32, the size of the metal nanoparticles 33 on the detection substrate 3 is about 1/3 of the wavelength of the light beam to be measured or smaller, and the surface of the detection substrate is perpendicular to the propagation direction of the light to be measured , the recording layer 32 faces the light beam to be measured.

The adjustable optical power attenuator 1 is used to adjust the light intensity; the exposure shutter 2 is used for the exposure operation, first adjust the optical power attenuator 1 and the exposure time 2, so that the recording layer on the detection substrate 3 after exposure produces a clear pattern, and Not burned by too high light power or too long exposure time; then take one more exposure. After the exposure, the recording layer of the probe substrate 3 is observed with a scanning electron microscope, and the position of the metal nanoparticles 33 and the surface morphology of the recording layer around them are recorded. The electric field distribution near the metal nanoparticles under the excitation of different polarization states is obtained by computational simulation. The surface morphology diagram of the recording layer obtained in the test is compared with the electric field distribution diagram obtained by calculation and simulation, so as to determine the polarization state of the light beam to be measured at the position of the detection substrate 3 .

In the embodiment, linearly polarized light is firstly used, and the electric field distribution diagram obtained through calculation and simulation is shown in FIG. 3 , in which the metal particle is at position 41 and the recording layer is at position 42 . The surface morphology of the recording layer obtained from the test is shown in Figure 4. It can be seen that the circle in the center of Figure 4 is the position of the metal nanoparticles, and the vertical stripes on the left and right sides of it coincide with the two intensity maximum positions of the recording layer in Figure 3, which proves that the polarization state of the measured beam is linear polarization. Then this embodiment uses longitudinally polarized light, and the electric field distribution diagram obtained by calculation and simulation is shown in FIG. 5 , in which the metal particle is at position 51 and the recording layer is at position 52 . The surface morphology of the recording layer obtained from the test is shown in Figure 6. It can be seen that there is only a central circular pattern in Figure 6, and its position coincides with the position of the circular intensity maximum area at the position of the recording layer directly under the metal nanoparticles in Figure 5, which proves that the polarization state of the measured beam is longitudinal polarization. This example proves that the method for directly measuring the polarization state of longitudinally polarized light based on surface plasmons proposed in the present invention is feasible and effective.

The concrete steps of the inventive method are as follows:

(1) Fabricate the detection substrate with the structure shown in Figure 2;

(2) Place an adjustable optical power attenuator and an exposure shutter in sequence on the optical path of the beam to be measured, and place a detection substrate at the end of the optical path, that is, where the polarization state of the light needs to be measured;

(3) Adjust the optical power to the range that meets the measurement requirements through the adjustable optical power attenuator;

(4) Adjust the exposure time of the exposure shutter for one exposure;

(5) Use a scanning electron microscope to observe the irradiated area of the detection substrate during the exposure process, and record the location of the metal nanoparticles on the recording layer in this area and the surface morphology near it;

(6) Obtain the electric field distribution map near the position of the metal nanoparticles on the recording layer on the detection substrate through calculation and simulation, and then compare the surface morphology obtained in the process (5) with the simulation results to determine the beam to be measured the polarization state.

Claims (1)

1. A kind of 1. method based on surface plasma direct measurement vertically polarized light polarization state, it is characterised in that specifically include Following steps：

   1）Make detection substrate, detection substrate include glass substrate, be attached to glass substantially with glass substrate area identical The chromium thin film recording layer of 200 nanometer thickness, and metal nanoparticle on the recording layer, metal nanoparticle on recording layer Size is 1/3 or so of tested light beam wavelength；

   2）Adjustable light power attenuator and exposure shutter are sequentially placed in the light path of light beam to be measured, in the end of light path, also It is that detection substrate is placed in the position for measuring light polarization state, band light-metering impinges perpendicularly on recording layer；

   3）In the range of adjustable light power attenuator regulating optical power to coincidence measurement requirement；

   4）The time for exposure of regulation exposure shutter, light beam to be measured is by adjustable light power attenuator and exposes shutter, then vertically Incide on detection substrate, carry out single exposure；

   5）Observed using the SEM region illuminated in exposure process to detection substrate, note down this region Metal nanoparticle present position and its neighbouring surface topography on interior recording layer；

   6）By calculating simulation, obtain detecting the Electric Field Distribution on substrate on recording layer near metal nanoparticle present position Figure, then by step 5）In obtained surface topography contrasted with analog result, determine the polarization state of light beam to be measured.