Polarimeter with CO2 laser

The company BBT - MATERIALS PROCESSING has long been engaged in the development and production of unique infrared polarization optics and acousto-optics for laser technology, photonics and materials research in space. For its development, the company requested an assembly designed to measure the optical transmittance of samples as a function of the polarization of the incident light. In view of the company's focus, the requirement was for measurements in the mid-infrared (MIR) region. In addition to the assembly of the optical path itself, part of the request was to completely cover the assembly to make the measurements safe for the operator.

The light source chosen was an air-cooled_CO2 industrial Diamond laser from Coherent operating at a wavelength of 9.3 µm. The output from this laser is linearly polarized (100:1) and achieves a power output of up to 17 W. The optical path of the assembly is further designed to allow for variation of the diameter, intensity and plane of polarization of the beam incident on the sample. The set laser intensity can be monitored by a control sensor inserted into the adjacent arm of the optical path for this purpose. This was also necessary in view of the fact that the laser used is an industrial source for which extremely high temporal stability of the output power is not typically required. To facilitate the measurement setup, a red guide laser is then integrated into the setup, which points in the sample plane to the same location as the measurement beam. Finally, a stray radiation detector is placed behind the sample.

All the optical components of the assembly are placed on a common substrate for which a protective cover has been fabricated. The control of the experiment is possible entirely via a PC that communicates with the individual peripherals of the assembly via a USB interface. The signal from the end detector is output via a coaxial cable for connection to an external measuring instrument (oscilloscope).

Device parameters

• _CO2 laser with a working wavelength of 9.3 µm and power up to 17 W
• Adjustable intensity incident on the sample in the range 0 - 100%
• Degree of polarization of the measuring beam in the sample plane up to 10000:1
• Experiment control via USB interface + detector signal output via coaxial (BNC) cable
• Encapsulation meeting the requirements for Class I laser equipment