OSA's Digital Library

Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 18, Iss. 20 — Sep. 27, 2010
  • pp: 21410–21418
« Show journal navigation

Fast ellipsometric measurements based on a single crystal photo-elastic modulator

R. Petkovšek, Jaka Petelin, J. Možina, and F. Bammer  »View Author Affiliations


Optics Express, Vol. 18, Issue 20, pp. 21410-21418 (2010)
http://dx.doi.org/10.1364/OE.18.021410


View Full Text Article

Acrobat PDF (1224 KB)





Browse Journals / Lookup Meetings

Browse by Journal and Year


   


Lookup Conference Papers

Close Browse Journals / Lookup Meetings

Article Tools

Share
Citations

Abstract

For quality control in high volume manufacturing of thin layers and for tracking of physical and chemical processes, ellipsometry is a common measurement technology. For such kinds of applications we present a novel approach of fast ellipsometric measurements. Instead of a conventional setup that uses a standard photo-elastic modulator, we use a 92 kHz Single Crystal Photo-Elastic Modulator (SCPEM), which is a LiTaO3 crystal with a size of 28 × 9 × 4 mm. This small, simple, and cost-effective solution also offers the advantage of direct control of the retardation via the current amplitude, which is important for repeatability of the measurements. Instead of a Lock-In Amplifier, an automated digital processing based on a fast analog to digital converter controlled by a highly flexible Field Programmable Gate Array is used. This and the extremely compact and efficient polarization modulation allow fast ellipsometric testing where the upper limit of measurement rates is mainly limited by the desired accuracy and repeatability of the measurements. The standard deviation that is related to the repeatability +/–0.002° for dielectric layers can be easily reached.

© 2010 OSA

1. Introduction

Ellipsometry plays an important role in many applications like thin coatings, photovoltaic devices, semiconductor devices, flat panel displays, optoelectronic devices, and biological and chemical engineering. Ellipsometry measures the polarizing effect of a sample via the ellipsometric angles ψ and Δ in order to deduce basic physical parameters such as the thickness and refractive index of optical layers [1

1. H. G. Tompkins, A Users's Guide to Ellipsometry, Academic Press Inc., London (1993).

]. For this the polarization of the probe light beam needs to be changed in a defined manner during the measurement. How this is done divides ellipsometers into three categories, namely with slow (based on rotating wave-plates [1

1. H. G. Tompkins, A Users's Guide to Ellipsometry, Academic Press Inc., London (1993).

,10

10. S.-M. F. Nee, “Error analysis of null ellipsometry with depolarization,” Appl. Opt. 38(25), 5388–5398 (1999). [CrossRef]

,11

11. H. Zhu, L. Liu, Y. Wen, Z. Lü, and B. Zhang, “High-precision system for automatic null ellipsometric measurement,” Appl. Opt. 41(22), 4536–4540 (2002). [CrossRef] [PubMed]

]), medium (with liquid crystals retarders [3]), and fast polarization modulation (based on a PEM – Photo-Elastic Modulator [2

2. B. Drévillon, J. Perrin, R. Marbot, A. Violet, and J. L. Dalby, “Fast polarization modulated ellipsometer using a microprocessor system for digital Fourier analysis,” Rev. Sci. Instrum. 53(7), 969–977 (1982). [CrossRef]

,4

4. C.-Y. Han and Y.-F. Chao, “Photoelastic modulated imaging ellipsometry by stroboscopic illumination technique,” Rev. Sci. Instrum. 77(2), 023107 (2006). [CrossRef]

,5

5. M. V. Khazimullin and Y. A. Lebedev, “Fourier transform approach in modulation technique of experimental measurements,” Rev. Sci. Instrum. 81(4), 043110 (2010). [CrossRef] [PubMed]

,8

8. A. Zeng, L. Huang, Z. Dong, J. Hu, H. Huang, and X. Wang, “Calibration method for a photoelastic modulator with a peak retardation of less than a half-wavelength,” Appl. Opt. 46(5), 699–703 (2007). [CrossRef] [PubMed]

,12

12. S. N. Jasperson and S. E. Schnatterly, “An improved method for high reflectivity ellipsometry based on a new polarization modulation technique,” Rev. Sci. Instrum. 40(6), 761–767 (1969). [CrossRef]

]). The first method produces extremely accurate results +/–0.001° at very low sampling rates (several seconds for one sample). The second method is faster with less accuracy, and the third, to which our setup belongs, currently achieves sampling rates of up to 1 kHz with accuracy +/–0.01°. The modulator is in this case composed of one piece of glass that is excited on a resonance frequency with one or two actuators [6

6. J. C. Kemp, “Piezo-optical birefringence modulators: new use for a long-known effect,” J. Opt. Soc. Am. 59, 950–954 (1969).

,7

7. J. C. Canit and J. Badoz, “New design for a photoelastic modulator,” Appl. Opt. 22(4), 592–594 (1983). [CrossRef] [PubMed]

]. The resulting mechanical oscillation induces a modulated birefringence in the glass, via the photo-elastic effect, and hence a modulated polarizing effect. Combinations of different ellipsometric methods are also possible [14

14. K. Postava, A. Maziewski, T. Yamaguchi, R. Ossikovski, S. Višnovsky, and J. Pištora, “Null ellipsometer with phase modulation,” Opt. Express 12(24), 6040–6045 (2004), http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-12-24-6040. [CrossRef] [PubMed]

].

The ellipsometric parameters ψ and Δ can be calculated from the 0th, 1st, and 2nd harmonics of the signal of the photo diode (Section 2). These are usually measured with a Lock-In Amplifier.

The main advantage of our setup is the usage of a single piezo-electric crystal as a modulator, which in comparison to a conventional PEM, which is composed of at least two glued components, is more favorable in terms of size, price, control, and handling [9

9. F. Bammer, B. Holzinger, and T. Schumi, “A single crystal photo-elastic modulator,” Proc. SPIE 6469, 1–8 (2007).

,13

13. R. Petkovsek, F. Bammer, D. Schuöcker, and J. Mozina, “Dual-mode single-crystal photo-elastic modulator and possible applications,” Appl. Opt. 48(7), C86–C91 (2009). [CrossRef] [PubMed]

]. The crystal is made of LiTaO3, with dimensions of 28 × 9.5 × 4 mm in x-, y-, and z-coordinates. The light travels along the z-axis, which is the optical axis (this crystal from the crystal symmetry group 3m is uniaxial). The electrodes are on the y-surfaces and a longitudinal x-oscillation is excited. The voltage amplitude for half wave retardation amplitude for 633 nm is ~2V.

This solution approach enables easier and more direct control of optical retardation as there is no transmission of the mechanical oscillation from an actuator to the optical modulator.

The evaluation is digital, as first demonstrated in [2

2. B. Drévillon, J. Perrin, R. Marbot, A. Violet, and J. L. Dalby, “Fast polarization modulated ellipsometer using a microprocessor system for digital Fourier analysis,” Rev. Sci. Instrum. 53(7), 969–977 (1982). [CrossRef]

], where a spectroscopic ellipsometer based on a classical PEM is presented. Due to the limitations of electronics and due to the use of a lamp (as necessary for spectroscopic ellipsometry) the accuracy and measurement velocity is much lower than in the system presented here. Further we refer to recent work [5

5. M. V. Khazimullin and Y. A. Lebedev, “Fourier transform approach in modulation technique of experimental measurements,” Rev. Sci. Instrum. 81(4), 043110 (2010). [CrossRef] [PubMed]

], where a detailed error analysis for a digital (Fourier) evaluation is presented and applied to a birefringence measurement, based again on a classical PEM, and similar to an ellipsometric measurement.

Our setup uses custom-made electronics, which is also very important for driving the SCPEM as well as for data acquisition and processing. It is based on a Field Programmable Gate Array (FPGA), which replaces the conventional Lock-In Amplifier usually used in PEM-based ellipsometers and enables high sampling rates with high flexibility.

This approach realizes high sampling rates with sufficient repeatability with a compact design. Here one must distinguish between absolute or relative accuracy and repeatability. The latter, which makes an evaluation based on the constancy of the signals for a continuous measurement on a constant sample, is decisive for monitoring applications for which our system is especially suited due to the high sampling rate. As the system is mainly intended for the measurement of fast temporal or spatial changes in layer thickness or its optical properties, it is therefore more important to have high repeatability than high absolute accuracy.

We mention that it is straightforward to extend this method to spectroscopic ellipsometry [2

2. B. Drévillon, J. Perrin, R. Marbot, A. Violet, and J. L. Dalby, “Fast polarization modulated ellipsometer using a microprocessor system for digital Fourier analysis,” Rev. Sci. Instrum. 53(7), 969–977 (1982). [CrossRef]

] and, with a synchronized pulsed light source, to imaging ellipsometry, as done with a conventional PEM in [4

4. C.-Y. Han and Y.-F. Chao, “Photoelastic modulated imaging ellipsometry by stroboscopic illumination technique,” Rev. Sci. Instrum. 77(2), 023107 (2006). [CrossRef]

]. In the latter case the angle-dependent natural birefringence of the crystal must be taken into account [9

9. F. Bammer, B. Holzinger, and T. Schumi, “A single crystal photo-elastic modulator,” Proc. SPIE 6469, 1–8 (2007).

].

2. Theoretical background of fast ellipsometry

Figure 1
Fig. 1 Schematic diagram of a PEM-based ellipsometer
shows the optical setup of a typical ellipsometric measurement with a photo-elastic modulator. The polarization of the light from the low noise laser source is oriented at 45° with respect to the axis perpendicular to the figure plane. The optical axis (z-axis) of the modulator is parallel to the laser beam in the case of ideal adjustment. The x-axis of the crystal is parallel to the paper plane.

The modulator changes the phase of the p-polarization with respect to the s-polarization by an angle (or retardation) δ, which varies according to:
δ=δ0+δ1sinΩt
(1)
δ 0 is the retardation dc-value or off-set (depending on pre-stresses and on the parallelism between the light beam and the optical axis of the crystal), δ 1 is the amplitude of the 1st harmonic of the retardation course, and Ω is the modulator frequency

The ellipsometric angles ψ and Δ are defined for a reflection as
tanψ=|Rp|/|Rs|,   Δ=argRpargRs,
(2)
where R p and R s are the complex reflection coefficients for p- and s-polarized light, respectively. Their measurement within the setup of Fig. 1 uses a polarization-modulated light beam. The reflected beam passes an analyzer and hits a detector that records the temporal dependency of the resulting intensity. For a proper sample without any depolarizing effect the temporal transmission course T through the analyzer is now given by
T=(1+tan2ψ+2tanψcos(ΔS+δ1sinωt))/4,
(3)
with ΔS = Δ + δ 0. If now the dc-value component I 0 and the first two harmonics components I 1,2 of this function are calculated, one obtains the following relations: (J 0,1,2 are the 0th, 1st, and 2nd order Bessel functions):

I1I0=4J1(δ1)sinΔStanψ1+tan2ψ2J0(δ1)tanψcosΔSI2I0=4J2(δ1)sinΔStanψ1+tan2ψ2J0(δ1)tanψcosΔSI1I2=J1(δ1)J2(δ1)tan ΔS
(4)

By adjusting the retardation amplitude to δ 1 = δB = 2.4048…rad, which corresponds to the first zero of J 0, the ratios of the first harmonic to the DC component and the second harmonic to the DC component are given by:

I1I0=4J1(δB)sinΔStanψ1+tan2ψ,I2I0=4J2(δB)cosΔStanψ1+tan2ψ
(5)

In order to calculate the ellipsometric angles from the ratio of the particular components it is useful to introduce the following intensity ratio:
I˜=(1J1(δB)I1I0)2+(1J2(δB)I2I0)2=4tanψ1+tan2ψ
(6)
Then we can finally obtain the ellipsometric angles.
tanψ=2±4I˜2I˜,   tanΔS=J2(δ1)I1J1(δ1)I2
(7)
The equation for ψ holds only for δ 1 = δB, whereas that for ΔS holds for all δ 1.

To judge now the sensitivity of the measurement on errors of I 0, I 1, I 2, and δ, the partial derivatives of Δ, and ψ as functions of δ, I 0,1,2 can be calculated. Figures 2
Fig. 2 Influence of initial retardation inaccuracy (a) and inaccuracy of I 1/I 2 (b); measurement on absolute deviation of ellipsometric angle Δ.
and 3
Fig. 3 Influence of initial retardation inaccuracy (a) and inaccuracy of I 1/I 0 (b) as well I 2/I 0 (c); measurement on absolute deviation of ellipsometric angle ψ.
show these as functions of Δ and ψ. Obviously ψ-values near 45° are difficult to measure, since all partial derivatives of ψ show a singularity at ψ = 45°. Small inaccuracies in the measurement of the harmonics I 0,1,2 or a small deviation of δ 1 from the desired value then cause large errors.

3. Experimental setup

The laser source is an ultra low noise laser diode (RMS noise 0.06% in the bandwidth from 10 Hz to 10 MHz, wavelength 635 nm, 4 mW). The extinction rates of the polarizers are approximately 1:105. We used several samples: glass, sapphire, polished aluminum, copper, steel, and zinc.

3.1 Calibration of retardation

To directly measure the retardation amplitude and to calibrate the SCPEM one has to check the light intensity I going through parallel polarizers with the SCPEM in between, tilted by 45° around the optical path. It is sufficient to track the dc-value I 0 in dependence on δ 1 [6

6. J. C. Kemp, “Piezo-optical birefringence modulators: new use for a long-known effect,” J. Opt. Soc. Am. 59, 950–954 (1969).

]:
I0(δ1)I0(0)=1+J0(δ1)2
(8)
For example, if δ 1 is exactly the first zero of the 0th Bessel function (J 0(δ 1) = 0 → δ 1 = δB = 2.4048…), I 0 takes exactly 50% of the value measured at δ 1 = 0.

3.2 Control of retardation

This linear relation allows control of the retardation via control of the current. When the excitation frequency f is tuned to any resonance frequency f R, where a sharp resonance peak is found, current and retardation are extremely sensitive to small changes in frequency, which must therefore be controlled with high precision. However the linear relation between the current and retardation amplitude is constant only within the resonance bandwidth f FWHM (typically f R/f FWHM = ~5000):
δ1i1const    for    fRfFWHM2<f<fR+fFWHM2
(9)
Due to this relation, the measurement and precise control of the current amplitude i 1 are of utmost importance to keep the retardation amplitude δ 1 at the desired value.

3.3 SCPEM driver and measuring unit

A schematic diagram of the driver and the measuring units is presented in Fig. 5
Fig. 5 Schematic diagram of driver and measuring unit
.

The role of the driver unit is to keep the retardation amplitude of the modulator fixed. For the dynamic ellipsometric measurements it is very important to control the retardation amplitude of the modulator very precisely. How the retardation amplitude affects the final results can be seen from Figs. 2(a) and 3(a), which show the influence of variation in initial retardation on ellipsometric angles. The retardation amplitude of the SCPEM is directly proportional to the electrical current. Within the resonance bandwidth the factor between both values is constant (Eq. (9)). The resonance peak of the SCPEM used in our experiments is quite narrow (relative FWHM is in the range of 10−4). Therefore the electronics must first precisely control the frequency and second stabilize the current amplitude. This is realized by a digital measurement of current amplitude and phase. The information on amplitude is used for current stabilization and retardation adjustment. The phase information is used to lock the electronic clock frequency to the crystal resonance frequency with high relative accuracy (better than 10−6).

In the measuring unit the photodiode signal is converted to a digital signal by using a fast and precise 14 bit analog to digital converter (ADC). Signal components that correspond to the DC, first harmonic, and second harmonic contribution are separated from the initial signal by digital signal processing. The time that is needed for a single measurement directly depends on the acquisition time. It is determined by the ADC clock frequency and the number of captured samples per single measurement. Therefore in order to achieve a lower acquisition time, the number of sampling points has to be decreased and/or the sampling frequency has to be increased. However due to the high frequency noise of the system that comes from the photodiode, amplifiers, and ADC, there is a limit to the sampling frequency. Above this limit the repeatability of the system deteriorates. Furthermore the number of sampling points of course directly influences the accuracy and repeatability. Therefore there is a trade-off between the repeatability of the measurements and acquisition time.

4. Results and discussion

Typical intensity courses for different dielectric and metallic surfaces are shown in Fig. 6
Fig. 6 Typical waveform corresponding to reflection from: dielectric surfaces: sapphire and glass (upper two graphs); metal surfaces: stainless steel and copper (lower two graphs). Vertical axes represent amplitude normalized to 1.
clearly showing the first and second harmonic components of the photodiode signal. From the upper left graph to the bottom right the share of the first harmonic component I 1 is increasing. As clearly shown by Eq. (7), the ellipsometric angle Δ depends on I 1/I 2. A higher share of the first harmonic I 1 means a lower Δ (for 90° < Δ < 180°). Therefore for the dielectric material Δ is close to 180°, and for the metals Δ is much smaller.

Examples of series of consecutive measurements of Δ angle for dielectric surfaces are presented in Fig. 7
Fig. 7 Typical repeatability of ellipsometric angles measurement for dielectric surfaces (glass, sapphire) for acquisition times of 0.3 ms and 20 ms (in degrees).
. The lower and upper two graphs represent measurements taken at acquisition times of 0.3 ms and 20 ms respectively. Obviously a longer acquisition time leads to better repeatability, as expected. From the graphs it is also clear that there is no significant drift in measurements and therefore the repeatability can be well represented by the standard deviation of the measurement.

The effect of acquisition time on standard deviation is summarized in Table 1

Table 1. Influence of acquisition time on repeatability of results for Δ obtained from measurement for different dielectric and metallic surfaces. In general a longer acquisition time corresponds to a lower standard deviation and therefore to better repeatability of the results.

table-icon
View This Table
| View All Tables
. Clearly the standard deviation increases with decreasing acquisition time, which can in principle be reduced to the period time of the SCPEM-oscillation, i.e. to nearly 10µs. A further reduction is possible by the usage of an SCPEM with higher frequency; up to 1 MHz can be realized rather easy, corresponding to acquisition times of 1µs.

The difference in the standard deviation of angle ψ corresponding to dielectric and metal surfaces is much higher. For the metal ψ is close to 45°. From Fig. 3(a) it is clear that in that case ψ is very sensitive to any variation in the initial retardation δ 1 and therefore to variation in the electrical current of the modulator. Furthermore, any variation in the measurement that is reflected in the variation of the ratio of I 1 and I 0 as well as I 2 and I 0 also strongly influences the standard deviation of the final results and therefore the repeatability of the final value of ψ, when this angle is close to 45° – see Figs. 3(a) and 3(b).

5. Conclusion

In general, as expected the repeatability strongly depends on acquisition time, which was tested with this prototype in the range 0.03–20 ms. Even shorter acquisition times are possible. A further development is planned to increase the working frequency by using higher harmonics of the SCPEM or by using a different crystal with a higher fundamental frequency. The proposed measurement device is ideally suited for monitoring applications, quality control for large volume production (for example thin film control in photovoltaic panel production), and tracking of fast physical and chemical reactions.

References and links

1.

H. G. Tompkins, A Users's Guide to Ellipsometry, Academic Press Inc., London (1993).

2.

B. Drévillon, J. Perrin, R. Marbot, A. Violet, and J. L. Dalby, “Fast polarization modulated ellipsometer using a microprocessor system for digital Fourier analysis,” Rev. Sci. Instrum. 53(7), 969–977 (1982). [CrossRef]

3.

Product bulletin,http://www.hindsinstruments.com/wp-content/uploads/Abrio-Product-Bulletin.pdf

4.

C.-Y. Han and Y.-F. Chao, “Photoelastic modulated imaging ellipsometry by stroboscopic illumination technique,” Rev. Sci. Instrum. 77(2), 023107 (2006). [CrossRef]

5.

M. V. Khazimullin and Y. A. Lebedev, “Fourier transform approach in modulation technique of experimental measurements,” Rev. Sci. Instrum. 81(4), 043110 (2010). [CrossRef] [PubMed]

6.

J. C. Kemp, “Piezo-optical birefringence modulators: new use for a long-known effect,” J. Opt. Soc. Am. 59, 950–954 (1969).

7.

J. C. Canit and J. Badoz, “New design for a photoelastic modulator,” Appl. Opt. 22(4), 592–594 (1983). [CrossRef] [PubMed]

8.

A. Zeng, L. Huang, Z. Dong, J. Hu, H. Huang, and X. Wang, “Calibration method for a photoelastic modulator with a peak retardation of less than a half-wavelength,” Appl. Opt. 46(5), 699–703 (2007). [CrossRef] [PubMed]

9.

F. Bammer, B. Holzinger, and T. Schumi, “A single crystal photo-elastic modulator,” Proc. SPIE 6469, 1–8 (2007).

10.

S.-M. F. Nee, “Error analysis of null ellipsometry with depolarization,” Appl. Opt. 38(25), 5388–5398 (1999). [CrossRef]

11.

H. Zhu, L. Liu, Y. Wen, Z. Lü, and B. Zhang, “High-precision system for automatic null ellipsometric measurement,” Appl. Opt. 41(22), 4536–4540 (2002). [CrossRef] [PubMed]

12.

S. N. Jasperson and S. E. Schnatterly, “An improved method for high reflectivity ellipsometry based on a new polarization modulation technique,” Rev. Sci. Instrum. 40(6), 761–767 (1969). [CrossRef]

13.

R. Petkovsek, F. Bammer, D. Schuöcker, and J. Mozina, “Dual-mode single-crystal photo-elastic modulator and possible applications,” Appl. Opt. 48(7), C86–C91 (2009). [CrossRef] [PubMed]

14.

K. Postava, A. Maziewski, T. Yamaguchi, R. Ossikovski, S. Višnovsky, and J. Pištora, “Null ellipsometer with phase modulation,” Opt. Express 12(24), 6040–6045 (2004), http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-12-24-6040. [CrossRef] [PubMed]

OCIS Codes
(120.2130) Instrumentation, measurement, and metrology : Ellipsometry and polarimetry
(230.4110) Optical devices : Modulators
(260.2130) Physical optics : Ellipsometry and polarimetry
(240.2130) Optics at surfaces : Ellipsometry and polarimetry

ToC Category:
Instrumentation, Measurement, and Metrology

History
Original Manuscript: July 28, 2010
Revised Manuscript: September 10, 2010
Manuscript Accepted: September 10, 2010
Published: September 23, 2010

Citation
R. Petkovšek, Jaka Petelin, J. Možina, and F. Bammer, "Fast ellipsometric measurements based on a single crystal photo-elastic modulator," Opt. Express 18, 21410-21418 (2010)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-18-20-21410


Sort:  Author  |  Year  |  Journal  |  Reset  

References

  1. H. G. Tompkins, A Users's Guide to Ellipsometry, Academic Press Inc., London (1993).
  2. B. Drévillon, J. Perrin, R. Marbot, A. Violet, and J. L. Dalby, “Fast polarization modulated ellipsometer using a microprocessor system for digital Fourier analysis,” Rev. Sci. Instrum. 53(7), 969–977 (1982). [CrossRef]
  3. Product bulletin, http://www.hindsinstruments.com/wp-content/uploads/Abrio-Product-Bulletin.pdf
  4. C.-Y. Han and Y.-F. Chao, “Photoelastic modulated imaging ellipsometry by stroboscopic illumination technique,” Rev. Sci. Instrum. 77(2), 023107 (2006). [CrossRef]
  5. M. V. Khazimullin and Y. A. Lebedev, “Fourier transform approach in modulation technique of experimental measurements,” Rev. Sci. Instrum. 81(4), 043110 (2010). [CrossRef] [PubMed]
  6. J. C. Kemp, “Piezo-optical birefringence modulators: new use for a long-known effect,” J. Opt. Soc. Am. 59, 950–954 (1969).
  7. J. C. Canit and J. Badoz, “New design for a photoelastic modulator,” Appl. Opt. 22(4), 592–594 (1983). [CrossRef] [PubMed]
  8. A. Zeng, L. Huang, Z. Dong, J. Hu, H. Huang, and X. Wang, “Calibration method for a photoelastic modulator with a peak retardation of less than a half-wavelength,” Appl. Opt. 46(5), 699–703 (2007). [CrossRef] [PubMed]
  9. F. Bammer, B. Holzinger, and T. Schumi, “A single crystal photo-elastic modulator,” Proc. SPIE 6469, 1–8 (2007).
  10. S.-M. F. Nee, “Error analysis of null ellipsometry with depolarization,” Appl. Opt. 38(25), 5388–5398 (1999). [CrossRef]
  11. H. Zhu, L. Liu, Y. Wen, Z. Lü, and B. Zhang, “High-precision system for automatic null ellipsometric measurement,” Appl. Opt. 41(22), 4536–4540 (2002). [CrossRef] [PubMed]
  12. S. N. Jasperson and S. E. Schnatterly, “An improved method for high reflectivity ellipsometry based on a new polarization modulation technique,” Rev. Sci. Instrum. 40(6), 761–767 (1969). [CrossRef]
  13. R. Petkovsek, F. Bammer, D. Schuöcker, and J. Mozina, “Dual-mode single-crystal photo-elastic modulator and possible applications,” Appl. Opt. 48(7), C86–C91 (2009). [CrossRef] [PubMed]
  14. K. Postava, A. Maziewski, T. Yamaguchi, R. Ossikovski, S. Višnovsky, and J. Pištora, “Null ellipsometer with phase modulation,” Opt. Express 12(24), 6040–6045 (2004), http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-12-24-6040 . [CrossRef] [PubMed]

Cited By

Alert me when this paper is cited

OSA is able to provide readers links to articles that cite this paper by participating in CrossRef's Cited-By Linking service. CrossRef includes content from more than 3000 publishers and societies. In addition to listing OSA journal articles that cite this paper, citing articles from other participating publishers will also be listed.


« Previous Article  |  Next Article »

OSA is a member of CrossRef.

CrossCheck Deposited