System for controlling intensity of a beam of electromagnetic radiation and method for investigating materials with low specular reflectance and/or are depolarizing

• US 7,821,637 B1
• Filed: 02/21/2008
• Issued: 10/26/2010
• Est. Priority Date: 02/22/2007
• Status: Active Grant

• Current Assignee: J.A. Woollam Co., Inc.
• Original Assignee: J.A. Woollam Co., Inc.
• Inventors: Liphardt, Martin M., Pfeiffer, Galen L., Hilfiker, James N.
• Primary Examiner(s): Chowdhury; Tarifur
• Assistant Examiner(s): LAPAGE, MICHAEL P
• Application Number:
  US12/070,824
• Time in Patent Office: 978 Days
• Field of Search: 356364-370, 356/239.8, 356/369, 356/491, 356/213, 257/21, 257/432
• US Class Current: 356/367
• CPC Class Codes: G01N 21/211 Ellipsometry optical thickness measurement G01B11/06
• CPC Class Codes: G01N 2201/124 Sensitivity

Abstract

Disclosed is a system for controlling focus, angle of incidence and intensity of an electromagnetic beam over a spectrum of wavelengths, and methodology for optimizing investigation of samples which demonstrate low specular reflectance and/or are depolarizing of a polarized beam of electromagnetic radiation, such as solar cells.

Claims

1. A method of investigating materials demonstrating depolarization using electromagnetic beams, comprising a procedure which comprises steps a, b and c, said steps a, b and c being:

a) providing a system comprising;

a source of electromagnetic radiation;

a polarizer;

a variable focusing means;

a depolarizing material sample;

an analyzer;

a detector of electromagnetic radiation;

arranged such that said source of electromagnetic radiation provides a beam of electromagnetic radiation which is directed to pass through said polarizer, said variable focusing means and impinge on said depolarizing sample at an angle of incidence thereto, partially reflect from said depolarizing material sample, pass through said analyzer and enter said detector of electromagnetic radiation such that said detector develops an output signal;

b) while monitoring said output signal from said detector and determining depolarization of the beam entering thereinto therefrom from;

% DEP=1−

√

{square root over (N²+C²+S²)}

where;

N=Cos(2ψ

);

C=Sin(2ψ

) cos(Δ

); and

S=Sin(2ψ

) Sin(Δ

);

varying the angle of incidence and degree of focusing provided by said variable focusing means, to determine a combination thereof which substantially minimizes depolarization associated with an output signal;

c) with the system configured as determined in steps a and b, obtaining data from the detector;

said method further comprising steps d and e, said steps d and e being;

d) practicing steps a and b to the end that the detector signal output represents an acceptable range of beam depolarization less than 35%, and

e) obtaining data from said detector by practice of step c;

said method being characterized by at least one selection from the group consisting of;

at least some obtained data is stored in machine readable media;

at least some obtained data is displayed electronically or by non-electronic means;

at least some obtained data is caused to be represented by a signal which is applied to provide a concrete and tangible result.

2. A method as in claim 1, wherein the angle of incidence is caused to be greater than about 75 degrees.

3. A method as in claim 1 in which said procedure further comprises providing at least one selection from the group:

a variable filter between said source of electromagnetic radiation and said detector;

a system comprising a control polarizer and a beam polarizer between said source and said sample; and

a system comprising a control polarizer, a control compensator and a beam polarizer between said source and said sample;

which can be applied to control the intensity of the electromagnetic radiation entering said detector;

and in which said method further includes the step of;

adjusting the selection to place the intensity of said electromagnetic radiation entering said detector into a range which does not saturate it.