CN104777623A - Method for determining minimum threshold incident angle of generating depolarization under high numerical aperture objective - Google Patents

Abstract

The invention discloses a method for determining the minimum threshold incident angle of generating depolarization under a high numerical aperture objective in the technical field of nano optical imaging. According to the method, a depolarization effect under the high numerical aperture objective is utilized, a Debye vectorial integral formula is adopted to obtain focusing plane vectorial optical field distribution; a rate of peak indexes of all components is acquired to obtain a depolarization conversion rate in the aperture half-angle range; then an aperture half angle is divided into n equal intervals; and a depolarization conversion rate of an optical field component in each interval is sequentially acquired by adopting the Debye vectorial integral formula, so that an interval upper limit value greater than the depolarization conversion rate in the aperture half-angle range is the minimum threshold incident angle of generating depolarization under the high numerical aperture objective. The method can be applied to a single nano particle high-sensitivity optical identifying and imaging system so as to obtain single nano particle amplitude and phase distribution under the high numerical aperture.

Description

The defining method of the minimum critical incident angle depolarized is produced under a kind of high-NA objective

Technical field

The invention belongs to nanocomposite optical technical field of imaging, relate to the problem of depolarizing of high-NA objective, be related specifically to a kind of high-NA objective and place an order and to produce the method that the minimum critical incident angle that depolarizes determines in the high sensitivity optical identification of nano particle and imaging system.

Background technology

High-NA objective has been widely used in scientific research and commercial Application at present, as medical science, and the field such as biology and nanocomposite optical.Optically carry out nano particle detection, theoretical according to Rayleigh scattering, particle scattering intensity is directly proportional to particle diameter, when using up irradiation particle, only have the incident light of few part can interact with nano particle, therefore utilizing optical means to detect nano particle is a very large challenge.But converging light can produce depolarization effect under high-NA objective condition, its light field component produced can make light efficiently converge to nano particle and interact with it, therefore determines that the conversion efficiency of depolarization effect is the important experiment condition of high sensitivity optical identification list nano particle.In addition, when focusing on high-NA objective, scalar diffraction theory cannot accurately describe focusing light field, needs to use Vector Diffraction Theory, and wherein relatively more conventional is debye vector integration.According to debye vector integral formula, the conversion ratio of depolarization effect and the incident angle of incident light have and are closely connected, increase along with incident angle and increase, therefore determining that the minimum critical incident angle of incident light is significant to the imaging efficiency improving ultra-sensitivity detection nano particle.

Summary of the invention

For nanometer imaging problem under the high-NA objective mentioned in above-mentioned background technology, the present invention utilizes the depolarization effect under high-NA objective, produces the defining method of the minimum critical incident angle depolarized under proposing a kind of high-NA objective.

The present invention utilizes the depolarization effect under high-NA objective, and obtain the conversion ratio of depolarization effect according to debye vector integral formula, the technical scheme of employing comprises the following steps:

Step 1: the defined formula according to numerical aperture: NA=n sin α, obtains the value of aperture semi-angle;

Wherein, α is aperture semi-angle; NA is the value of high-NA objective numerical aperture, NA>1; N is the refractive index of high-NA objective actuating medium;

Step 2: according to debye vector integral formula, calculate the Electric Field Distribution at focus area any point place P (x, y).When x linearly polarized light is incident, Electric Field Distribution formula is:

When y linearly polarized light is incident, Electric Field Distribution formula is:

Wherein θ is linearly polarized light incident angle, be polarized light position angle, A is constant value, makes θ _maxequal the value of step 1 mesoporous half-angle α, then the peak intensity ratio of each component of acquisition light field obtains the conversion ratio that depolarizes within the scope of aperture semi-angle;

Step 3: by range intervals [0, the θ of linearly polarized light incident angle in step 2 _max] be divided into the by stages such as n, namely

$[0,\frac{{\mathrm{\θ}}_{\max }}{(n-1)}],[\frac{{\mathrm{\θ}}_{\max }}{(n-1)},\frac{2{\mathrm{\θ}}_{\max }}{(n-1)}],...,[\frac{(i-1){\mathrm{\θ}}_{\max }}{(n-1)},\frac{i{\mathrm{\θ}}_{\max }}{(n-1)}],...,[\frac{(n-2){\mathrm{\θ}}_{\max }}{(n-1)},{\mathrm{\θ}}_{\max }],$

Wherein 1≤i≤n, obtains the peak intensity ratio of each component of light field under each interval successively, obtains the conversion ratio that depolarizes under each interval according to step 2;

Step 4: the conversion ratio that depolarizes obtained in depolarize conversion ratio and the step 2 in each interval step 3 obtained compares, if the former is greater than the latter, then produce the minimum critical incident angle depolarized under this interval higher limit is high-NA objective.

The present invention utilizes the depolarization effect under high-NA objective, the defining method of the minimum critical incident angle depolarized is produced under proposing a kind of high-NA objective, the method can be applicable to high sensitivity optical identification and the imaging system of single nano particle, nano particle amplitude and PHASE DISTRIBUTION thus acquisition high-NA objective places an order.

Accompanying drawing explanation

Figure 1A is x light field component peak intensity ratio and incident angle variation relation curve map under high-NA objective.

Figure 1B is y light field component peak intensity ratio and incident angle variation relation curve map under high-NA objective NA.

Fig. 1 C is z light field component peak intensity ratio and incident angle variation relation curve map under high-NA objective.

Embodiment

Be defined as example with angle during the incidence of NA=1.2, n=1.52, x linearly polarized light below to elaborate.It should be emphasized that it is only exemplary for the following describes, instead of in order to limit the scope of the invention and apply.

Produce a defining method for the minimum critical incident angle depolarized under high-NA objective, the method can be applicable to high sensitivity optical identification and the imaging system of single nano particle;

It is characterized in that following steps:

Step 1: according to numerical aperture defined formula, work as NA=1.2, during n=1.52, aperture semi-angle is 52 °;

Step 2: according to debye vector integral formula, calculate the Electric Field Distribution at focus area any point place P (x, y):

Obtaining each component peak intensity ratio of light field is: wherein | I _max| ²=| E _{x max}| ²+ | E _{y max}| ²+ | E _{z max}| ², then have the light of 12.32% to produce depolarization effect, wherein 0.27% be converted to y-polarisation light, 12.05% is converted to z polarized light.

Step 3: by the range intervals [0 of linearly polarized light incident angle in step 2,52 °] be divided into the by stages such as 52, and obtain each interval successively according to step 2 and to go down polarization conversion rate, x direction polarized component to taper off trend with incident angle increase as shown in Figure 1A, y durection component is increasing trend along with incident angle increases as shown in Figure 1B, and z durection component is increasing trend along with incident angle increases as shown in Figure 1 C;

Step 4: the polarized component only using y direction in single nanoparticle imaging system, therefore the conversion ratio that depolarized in the y direction in each interval obtained by step 3 depolarizes with the y direction that obtains in step 2 successively, conversion ratio contrasts, at [37 °, 38 °] the interval and above interval conversion ratio that depolarizes all is greater than the conversion ratio that depolarizes in step 2, therefore 37 ° be the high-NA objective determined in this example under produce the minimum critical incident angle depolarized.

The above; be only the present invention's preferably embodiment; but protection scope of the present invention is not limited in this; anyly be familiar with those skilled in the art in the technical scope that the present invention discloses; the change that can expect easily or replacement, all should be encompassed within technical protection scope of the present invention.Therefore, the protection domain that protection scope of the present invention should require with interest field is as the criterion.

Claims (1)

1. produce a defining method for the minimum critical incident angle depolarized under high-NA objective, it is characterized in that following steps:

Step 1: the defined formula according to numerical aperture: NA=nsin α, obtains the value of aperture semi-angle;

Wherein, α is aperture semi-angle; NA is the value of high-NA objective numerical aperture, NA > 1; N is the refractive index of high-NA objective actuating medium;

Step 2: according to debye vector integral formula, calculate the Electric Field Distribution at focus area any point place P (x, y).When x linearly polarized light is incident, Electric Field Distribution formula is:

When y linearly polarized light is incident, Electric Field Distribution formula is:

Wherein θ is linearly polarized light incident angle, be polarized light position angle, A is constant value, makes θ _maxequal the value of step 1 mesoporous half-angle α, then the peak intensity ratio of each component of acquisition light field obtains the conversion ratio that depolarizes within the scope of aperture semi-angle;

Step 3: by range intervals [0, the θ of linearly polarized light incident angle in step 2 _max] be divided into the by stages such as n, namely wherein 1≤i≤n, obtains the peak intensity ratio of each component of light field under each interval successively, obtains the conversion ratio that depolarizes under each interval according to step 2;

Step 4: the conversion ratio that depolarizes obtained in depolarize conversion ratio and the step 2 in each interval step 3 obtained compares, if the former is greater than the latter, then produces the minimum critical incident angle depolarized under this interval higher limit is high-NA objective.