Diffusing wave spectroscopy with heterodyne detection

Patent metadata

Field	Value
Publication number	US-10451537-B2
Application number	US-201715424581-A
Country	US
Kind code	B2
Filing date	Feb 3, 2017
Priority date	Feb 4, 2016
Publication date	Oct 22, 2019
Grant date	Oct 22, 2019

Abstract

Exemplary apparatus and methods are provided for analyzing a medium. The apparatus, which may be a diffusing wave spectroscopy apparatus, comprises a first beam splitter for splitting a light from the laser light source into an excitation light and a reference light. The excitation light is directed on to a first portion of the medium and then multiply scattered light is collected at a second portion of the medium, the second portion being different from the first portion. The reference light, which has been attenuated, is combined with the multiply scattered light and either a power spectrum or an autocorrelation function is calculated.

First claim

What is claimed is:

1. A method for analyzing a medium comprising:
receiving a light from a light source,
splitting, via a first optical element, the light into an excitation light and a reference light,
irradiating, via a directing element that receives the excitation light after the splitting step, a first portion of the medium with the excitation light,
collecting, via a collecting element that is spaced away and separate from the directing element, a sample light from a second portion of the medium that is different from the first portion of the medium, wherein the sample light is from the excitation light multiply scattered in the medium,
combining, via a second optical element that is spaced away and separate from the first optical element, the reference light with the sample light, wherein the second optical element receives the sample light from the collecting element after the collecting step,
inputting the combined lights to an optical detector, and
measuring or calculating a power spectrum or an intensity autocorrelation function from a signal output from the optical detector,
wherein an intensity of the reference light is such that, when in use, a ratio of an intersection of a y-axis and the measured or calculated intensity autocorrelation function to a root mean square (RMS) is greater than 2.

2. The method of claim 1 , wherein the ratio is greater than 3.

3. The method of claim 1 , further comprising a step of attenuating the intensity of the reference light before combining the reference light with the sample light.

4. The method of claim 1 , further comprising adjusting the intensity of the reference light so that the intensity of the reference light at the detector is greater than a tenth part of a noise level and less than the saturation intensity of the optical detector.

5. The method of claim 1 , further comprising adjusting the intensity of the reference light so that the intensity of the reference light at the detector is almost equal to a noise level.

6. The method of claim 1 , further comprising calculating particle flow data from the power spectrum or autocorrelation function and optionally displaying or recording the particle flow data.

7. The method of claim 1 , further comprising calculating viscosity data from the power spectrum or intensity autocorrelation function and optionally displaying or recording the viscosity data.

8. The method of claim 1 , wherein one or more of:
(i) the measured or calculated intensity autocorrelation function is a measured intensity autocorrelation function g 2 (τ) that is fitted using the following equation:
f 2 (τ)=1+β·exp(−τ/τ c ),

where β is the intersection of the y-axis and the measured or calculated intensity autocorrelation function, τ is the lag, and τ c is the decay time;
(ii) the intersection of the y-axis and the measured or calculated intensity autocorrelation function β and the decay time τ c are optimized so that the RMS is minimized; and
(iii) the RMS is calculated using the following equation:

RMS
=

1
N

⁢

(

g
2

⁡

(
τ
)

-

f
2

⁡

(
τ
)

)

2

,

where the root mean square is calculated over an interval τ 1 ≤τ≤τ 2 , where τ 1 is different from, or close or equal to, the minimum lag and τ 2 is a lag when the intensity autocorrelation function curve is close or equal to 1, and N represents a number of sampling between τ 1 and τ 2 .

9. The method of claim 1 , wherein respective centers of the first portion and the second portion of the medium are separated and spaced away by one of: 1 cm, 2 cm, 3 cm, 4 cm, 5 cm, 6 cm, 7 cm, 8 cm, 9 cm, and 10 cm.

10. An apparatus for analyzing a medium comprising:
at least one laser light source,
at least one first beam splitter for splitting a light from the laser light source into an excitation light and a reference light,
at least one directing element for irradiating the excitation light from the at least one first beam splitter at or to a first portion of the medium,
a collecting element for collecting multiply scattered light referred to as sample light at a second portion of the medium, the second portion being different from the first portion and the collecting element being spaced away and separate from the at least one directing element,
at least one second beam splitter for combining the sample light and the reference light, the at least one second beam splitter being spaced away and separate from the at least one first beam splitter, and the at least one second beam splitter operating to receive the collected sample light from the collecting element,
at least one detector for measuring the optical intensity of the combined light,
at least one limiting element located between the medium and the optical detector, and
at least one analyzer for measuring or calculating either a power spectrum or an intensity autocorrelation function,
wherein an intensity of the reference light is such that a ratio of an intersection of a y-axis and the measured or calculated intensity autocorrelation function to a root mean square (RMS) is greater than 2.

11. The apparatus of claim 10 , wherein the ratio is greater than 3.

12. The apparatus of claim 10 , further comprising an attenuating element for attenuating the reference light.

13. The apparatus of claim 12 , wherein the attenuating element is an optical attenuator.

14. The apparatus of claim 10 , wherein the apparatus is configured such that the excitation light has a greater intensity than the reference light.

15. The apparatus of claim 10 , wherein the apparatus is configured such that the intensity of the reference light at the detector is greater than a tenth part of a noise level and less than the saturation intensity of the optical detector.

16. The apparatus of claim 10 , wherein the apparatus is configured such that the intensity of the reference light at the detector is almost equal to a noise level.

17. The apparatus of claim 10 , wherein the second beam splitter comprises at least two ports, wherein the sample light is input to a first port having a higher transmission and the reference light is input to a second port having a lower transmission.

18. The apparatus of claim 10 , wherein the limiting element is a pinhole or an optical fiber.

Assignees

• Canon Usa Inc

Inventors

• Nakaji Haruo

Classifications

• G01N15/1429

  Signal processing · CPC title

• G01N11/02

  by measuring flow of the material · CPC title

• G01N21/474

  Details of optical heads therefor, e.g. using optical fibres · CPC title

• G01N2011/008

  optical properties · CPC title

• G01N15/1434 Primary

  Optical arrangements · CPC title