Setting Compensator To A Specific Retardance; Setting The Compensator At The Calibration Wavelength; Setting The Compensator For Other Wavelengths - THORLABS SBC-VIS Operation Manual

Soleil-Babinet Compensator Operations Manual – Doc # N0073-D01 Rev A Ver 1.4

3.0 Setting Compensator to a specific retardance

3.1 Setting the Compensator at the Calibration Wavelength

The calibration distance can be used to set the compensator to any fractional wave of retardance at the
calibration wavelength using the following relationship:
Xcal = calibration distance
N = desired retardance (in waves)
X = N * Xcal
SBC
Example:
Test wavelength = 632.8nm
Xcal = 14.55
N = 0.25 (i.e. quarter wave of retardance)
X = 14.55 * 0.25 = 3.638 = micrometer setting to get a quarter wave of retardance.
SBC

3.2 Setting the Compensator for Other Wavelengths

Sometimes it is not possible or convenient to calibrate the compensator at the operating wavelength. For
example; the compensator is to be used in a Nd:YAG system but for logistical reasons can only be calibrated
using a low power HeNe.
In such cases, the compensator target position can be extrapolated using the calibration obtained in 2.4.1
together with the basic retardance equations for the compensator. The following equation calculates the
compensator position at the target wavelength and retardance:
* λ
X = N * B(λ
SBC 2 2
where: X is the micrometer setting to obtain the desired retardance
SBC
For models SBC-VIS and SBC-IR, use equation B-1 in Appendix B for B(λ). For SBC-UV, use equation B-2.
(obtained from 2.4.1)
) / (λ * B(λ ) ) * Xcal
2 1 2
X is the calibration from 2.4.1
CAL
is the desired retardance at wavelength λ
N
2
λ
is the new wavelength
2
B(λ) is the birefringence of the SBC model
2
Page 9
(eq. 3-1)
(eq 3-2)