US 11,740,176 B2
Fast and accurate mueller matrix infrared spectroscopic ellipsometer
Stefan Schoeche, Lincoln, NE (US); Craig M. Herzinger, Lincoln, NE (US); Steven E. Green, Lincoln, NE (US); Martin M. Liphardt, Lincoln, NE (US); and James D. Welch, Omaha, NE (US)
Assigned to J.A. WOOLLAM CO., INC, Lincoln, NE (US)
Filed by J.A. WOOLLAM CO., INC., Lincoln, NE (US)
Filed on Jan. 18, 2022, as Appl. No. 17/803,029.
Claims priority of provisional application 63/288,441, filed on Dec. 10, 2021.
Prior Publication US 2023/0184671 A1, Jun. 15, 2023
Int. Cl. G01N 21/21 (2006.01)
CPC G01N 21/211 (2013.01) [G01N 2021/213 (2013.01); G01N 2201/021 (2013.01); G01N 2201/06113 (2013.01); G01N 2201/12 (2013.01)] 27 Claims
OG exemplary drawing
 
1. A method of investigating a sample with electromagnetic radiation in the mid-infrared spectral range, which reduces the effects of speckle and standing waves, comprising the steps of:
a) providing an ellipsometer or polarimeter system comprising:
a′) a quantum cascade laser source of high-brilliance, tunable electromagnetic radiation with emission wavelengths in the mid-infrared spectral range, said quantum cascade laser source comprising means for dithering the electromagnetic radiation output;
b′) a beam polarizing optical element;
c′) a first rotatable optical retarder or polarizer element;
d′) a stage for supporting a sample;
e′) a second rotatable optical retarder or polarizer element;
f′) a beam analyzing polarizer optical element;
g′) a single-point detector for infrared radiation which is not capable of resolving individual pulses of quantum cascade laser electromagnetic radiation;
said method being characterized in that:
during use said quantum cascade laser source of electromagnetic radiation operates in a continuous or quasi-continuous wave, so that individual pulses are not detected; and
during use the wavelength content of said continuous or quasi-continuous wave is dithered so that cyclically or randomly a sequential plurality of different wavelengths around a central wavelength is output; and
during use said detector provides output data based on an average of a multiplicity of pulses in said continuous or quasi-continuous dithered electromagnetic radiation input thereto; and
during use said rotatable optical retarder or polarizing elements continuously rotate at different frequencies of fixed ratio;
said method further comprising:
b) placing a sample on said stage for supporting a sample;
c) while causing said rotatable optical retarder or polarizing elements continuously rotate at different frequencies of fixed ratio, causing said quantum cascade laser source to provide a dithered continuous or quasi-continuous beam of electromagnetic radiation directed so that it passes through said:
beam polarizing optical element; and
first rotatable optical retarder or polarizer element;
interacts with said sample on said stage for supporting a sample;
then passes through said:
second rotatable optical retarder or polarizer element; and
beam analyzing polarizer optical element; and
enters said single-point detector for infrared radiation;
d) causing said single-point detector for infrared radiation to provide sample characterizing output data based upon said received dithered continuous or quasi-continuous beam of electromagnetic radiation; and
e) analyzing the data output by said single-point detector to provide sample characterizing information.