Abstract

Multispectral refractometers typically measure refractive index (RI) at discrete monochromatic wavelengths via a serial process. We report on the demonstration of a white light full-field imaging-based refractometer capable of instantaneous multispectral measurement of absolute RI of clear liquid-gel samples across the entire visible light spectrum. The broad optical bandwidth refractometer is capable of hyperspectral measurement of RI in the range 1.30–1.70 between 400 and 700 nm with a maximum error of 0.0036 units (0.24% of actual) at 414 nm for an η=1.50 sample. We present system design and calibration method details as well as results from a system validation sample.

© 2012 Optical Society of America

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References

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  1. W.-K. Chang, Y.-C. Chao, and M.-K. Yeh, Asia Pac. J. Clin. Nutr. 17, 116 (2008).
  2. N. A. Russo, A. O. Tonso, and E. E. Sicre, Opt. Laser Technol. 25, 109 (1993).
    [CrossRef]
  3. A. H. Varnam, and J. P. Sutherland, Milk and Milk Products: Technology, Chemistry, and Microbiology (Springer, 2001).
  4. M. Trojanowicz, Flow Injection Analysis: Instrumentation and Applications (World Scientific, 2000).
  5. T. M. Niemczyk, in Physical Methods in Modern Chemical AnalysisT. Kuwana, ed. (Academic, 1980).
  6. S. Singh, Phys. Scr. 65, 167 (2002).
    [CrossRef]
  7. H. A. Strobel and W. R. Heineman, Chemical Instrumentation: a Systematic Approach3rd ed. (Wiley, 1989).
  8. G. E. Fishter, in Applied Optics and Optical Engineering, Optical Instruments, Part 1, R. Kingslake, ed. (Academic, 1967).

2008

W.-K. Chang, Y.-C. Chao, and M.-K. Yeh, Asia Pac. J. Clin. Nutr. 17, 116 (2008).

2002

S. Singh, Phys. Scr. 65, 167 (2002).
[CrossRef]

1993

N. A. Russo, A. O. Tonso, and E. E. Sicre, Opt. Laser Technol. 25, 109 (1993).
[CrossRef]

Chang, W.-K.

W.-K. Chang, Y.-C. Chao, and M.-K. Yeh, Asia Pac. J. Clin. Nutr. 17, 116 (2008).

Chao, Y.-C.

W.-K. Chang, Y.-C. Chao, and M.-K. Yeh, Asia Pac. J. Clin. Nutr. 17, 116 (2008).

Fishter, G. E.

G. E. Fishter, in Applied Optics and Optical Engineering, Optical Instruments, Part 1, R. Kingslake, ed. (Academic, 1967).

Heineman, W. R.

H. A. Strobel and W. R. Heineman, Chemical Instrumentation: a Systematic Approach3rd ed. (Wiley, 1989).

Niemczyk, T. M.

T. M. Niemczyk, in Physical Methods in Modern Chemical AnalysisT. Kuwana, ed. (Academic, 1980).

Russo, N. A.

N. A. Russo, A. O. Tonso, and E. E. Sicre, Opt. Laser Technol. 25, 109 (1993).
[CrossRef]

Sicre, E. E.

N. A. Russo, A. O. Tonso, and E. E. Sicre, Opt. Laser Technol. 25, 109 (1993).
[CrossRef]

Singh, S.

S. Singh, Phys. Scr. 65, 167 (2002).
[CrossRef]

Strobel, H. A.

H. A. Strobel and W. R. Heineman, Chemical Instrumentation: a Systematic Approach3rd ed. (Wiley, 1989).

Sutherland, J. P.

A. H. Varnam, and J. P. Sutherland, Milk and Milk Products: Technology, Chemistry, and Microbiology (Springer, 2001).

Tonso, A. O.

N. A. Russo, A. O. Tonso, and E. E. Sicre, Opt. Laser Technol. 25, 109 (1993).
[CrossRef]

Trojanowicz, M.

M. Trojanowicz, Flow Injection Analysis: Instrumentation and Applications (World Scientific, 2000).

Varnam, A. H.

A. H. Varnam, and J. P. Sutherland, Milk and Milk Products: Technology, Chemistry, and Microbiology (Springer, 2001).

Yeh, M.-K.

W.-K. Chang, Y.-C. Chao, and M.-K. Yeh, Asia Pac. J. Clin. Nutr. 17, 116 (2008).

Asia Pac. J. Clin. Nutr.

W.-K. Chang, Y.-C. Chao, and M.-K. Yeh, Asia Pac. J. Clin. Nutr. 17, 116 (2008).

Opt. Laser Technol.

N. A. Russo, A. O. Tonso, and E. E. Sicre, Opt. Laser Technol. 25, 109 (1993).
[CrossRef]

Phys. Scr.

S. Singh, Phys. Scr. 65, 167 (2002).
[CrossRef]

Other

H. A. Strobel and W. R. Heineman, Chemical Instrumentation: a Systematic Approach3rd ed. (Wiley, 1989).

G. E. Fishter, in Applied Optics and Optical Engineering, Optical Instruments, Part 1, R. Kingslake, ed. (Academic, 1967).

A. H. Varnam, and J. P. Sutherland, Milk and Milk Products: Technology, Chemistry, and Microbiology (Springer, 2001).

M. Trojanowicz, Flow Injection Analysis: Instrumentation and Applications (World Scientific, 2000).

T. M. Niemczyk, in Physical Methods in Modern Chemical AnalysisT. Kuwana, ed. (Academic, 1980).

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Figures (6)

Fig. 1.
Fig. 1.

Refractometer system layout. (a) Top view. (b) Side view.

Fig. 2.
Fig. 2.

Raw white light image. Rows (y values) correspond to wavelengths with blue (400 nm) at the bottom and red (700 nm) at the top. Columns (x values) correspond to RI critical pixel locations, with RI decreasing from left (η=1.7) to right (η=1.3).

Fig. 3.
Fig. 3.

Wavelength calibration using Ne and Hg(Ar) lamps as input light sources. The inset is a composite of the two calibration lamp images. The plot is a column (x value) scan of a line through the middle of the inset image with the known light source spectral emission peaks labeled with corresponding wavelengths.

Fig. 4.
Fig. 4.

Data plot of linear relationship between pixel row location (y) and wavelength (λ).

Fig. 5.
Fig. 5.

Representative RI sample images for three liquid standards: (a) η=1.60, (b) η=1.51, and (c) η=1.39. Images are the averages of 3–4 repetitions analyzed via MATLAB for conversion to binary images and automatic detection of RI Pc’s). Hilbert transform and SavitzkyGolay filtering were utilized to aid in Pc extraction before binary conversion of the images.

Fig. 6.
Fig. 6.

Plot of experimental and actual (based on manufacturer-provided Cauchy coefficients) data for the validation 1.50 liquid-gel RI standard.

Tables (1)

Tables Icon

Table 1. Comparison of Actual (Based on Manufacturer-Provided Cauchy Coefficients) and Experimental RI Values for η=1.50 Liquid-Gel Sample, Based on the Implementation of Eq. (4) at Select Wavelengths Within the Spectral Bandwidth

Equations (4)

Equations on this page are rendered with MathJax. Learn more.

θc=sin1(η2/η1),
λ(y)=0.0554y+688.13.
Rs=D·Rp,
η(x,y)=1.74743.5108×105x7.0094×107y4.2454×109x2+1.7019×109y2.

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