Answer:  From its beginning, the J.A. Woollam Company has dedicated itself solely to the development and refinement of spectroscopic ellipsometry. The J.A. Woollam Company was founded in 1987 in response to commercial demand for ellipsometry technology which had been studied for decades at the University of Nebraska at Lincoln. Our efforts have led to over 50 patents and numerous awards.

Over half of J.A. Woollam employees are scientists and engineers dedicated to the advancement of this single technology. The J.A. Woollam possesses a level of expertise in spectroscopic ellipsometry that no other company can match. Our applications engineers have seen almost every ellipsometry application imaginable. This, combined with our versatile product line, allows the J.A. Woollam to provide excellent customer support for any application.

Our ellipsometry analysis software can tackle the most complex analysis while maintaining the ease of use necessary for industrial applications.  J.A. Woollam has worked hard to provide the best product available with an excellent level of support.  

Question:  Why Spectroscopic Ellipsometry? 
Why not use a Laser with a single wavelength instead?

Question:  Why not use a reflectometer instead of an ellipsometer?

Answer:  The main advantage of  phase modulation ellipsometers is a very fast, theoretical, data acquisition rate. They use a photo-elastic modulator that can operate at rates up to 50kHz. However, to achieve satisfactory signal to noise levels, longer integration times are required; otherwise a very intense light source such as a laser must be used. 

To perform spectroscopic measurements with phase modulation ellipsometers, the amplitude of the modulation must be adjusted at each wavelength in turn, so monochromatic light input is necessary, which makes simultaneous acquisition of spectroscopic ellipsometric data not possible. In this case, the advantages of such high modulation rate are lost because of the limited mechanical speed at which the monochromator can change wavelengths. A mechanical system is only as fast as it's slowest component, which in this case is the monochromator. 

J. A. Woollam monochromators have been specially designed for fast wavelength changes; this makes VASE instruments as fast, if not faster than any spectroscopic phase modulation ellipsometer on the market today. If a high data acquisition rate is important for a particular application, a diode array/CCD-based ellipsometer, like the M-2000 that simultaneously acquires data over the entire desired spectral range, is the best choice.

Traditional rotating element ellipsometers lose accuracy and precision when delta is at or near 0°  or 180°. Phase modulation ellipsometers suffer from a similar disadvantage when psi is near 0° or 45°. To overcome this delta insensitivity in a rotating element ellipsometer, a compensator element can be added.  This provides data sensitivity over the entire 0-360° delta range. For more details please read this article on compensators from the J.A. Woollam company newsletter.  

In general, spectroscopic phase modulation ellipsometers are difficult to construct and calibrate, and the modulators are very sensitive to temperature. The advantage which phase modulation ellipsometers have over rotating element ellipsometers is their lack of any mechanical moving parts. However, with current bearing technology and quality construction, rotating element ellipsometers will most likely be obsolete before mechanical failure occurs.  

• Reflectance (Rp and Rs).
• Polarization.
• Path length in film (Multiple angles probe physical thickness multiple times!)

Some samples are more sensitive at a certain angle of incidence. By changing the angle of incidence, one can maximize the sample's sensitivity to a given parameter of interest.  This helps to determine multiple unknowns in difficult samples. Acquiring data at multiple angles ensures optimum sensitivity to any sample. Often times the flexibility of a VASE instrument is key in characterizing a material.