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Birefringence Modulator: Advantages

Modulator Comparison

The standard method is to drive the vibration using the piezoelectric properties of crystalline quartz. A drive crystal is attached to the optical element, and both are set into mechanical vibration using a power amplifier drive. This method however is very subject to variations in losses in the components, and to temperature drifts. Devices manufactured this way have been the source of many frustrations.

The Beaglehole Instruments Birefringence Modulator uses a unique three component device, with the optical element sandwiched between two crystal quartz pieces. One crystal quartz is used as the driver, the other (via the inverse piezoelectric effect) as a gauge of the vibrational amplitude. The feedback circuit is designed to hold the gauge signal at a constant level with minimal drift. The device is now completely insensitive to changes in temperature and vibrational losses. In spectroscopic applications, it is crucial that the phase shift is kept constant through the entire wavelength range. With the three-element Birefringence Modulator, the gauge signal provides a direct monitor of the birefringence, without the need of elaborate on-line calibration methods. Furthermore, there is no need for temperature stabilization of the optical head.

The design of the Birefringence Modulator is very reliable and greatly simplifies the setup of high-sensitivity instruments. Applications include measurement of birefringence, dichroism, and other polarisation effects. It is used in our Picometer Ellipsometer for very fast high sensitivity ellipsometry measurements. The Birefringence Modulator can easily be included in any optical setup. The unit can be remotely controlled through an analog input voltage - calibration software routines are provided. An AD/DA interface board for IBM compatible PCs is available. The Birefringence Modulator can also be controlled through our universal measurement control interface, consisting of an external microcontroller and a graphical user interface running on WindowsNT. This configuration features automatic calibration and real-time data acquisition from up to 6 inputs. Contact us for more information.