Combination of excimer and CO2 laser beams

The customer from the BIOCEV research centre has been studying biopolymers such as proteins, nucleic acids and carbohydrates for a long time. To analyse them, he used, among other things, mass spectroscopy, in which information is extracted from fragments of the original polymers. In the existing set-up, the customer obtained these fragments by dissociating the polymers using a CO2 laser fed directly into the vacuum chamber of the spectrometer.

Now the customer wanted to add the possibility to dissociate the polymers in the chamber using an excimer laser, whose 193 nm wavelength reacts with the polymers in a significantly different way than the infrared radiation of the CO2 laser (10.2 um). Thus, the basic challenge of the project was to guide the lasers into the same path so that one, the other or both could be used simultaneously.

Putting the lasers in the same path should normally be a relatively simple task. In our case, however, the situation was complicated by the lack of a suitable dichroic mirror for the combination of 193 nm and 10.2 um wavelengths. The laser that should not have passed into the chamber was diverted and safely absorbed in the "beam dump". Thanks to a table movement speed of up to 250 mm/s, the possibility of switching between lasers with a frequency of up to 10 Hz was achieved.

The control of the mirror table and both lasers was realized by electronics designed by us. This was particularly important in view of the necessary synchronization of the lasers with the oscillation of the mirror. We were able to integrate all the electronics into a housing that was already part of the customer's original setup. The experiment is then controlled by our own control software, which was designed for this purpose and delivered with the setup. Another important part of the system was to cover the optical path of the excimer laser. The enclosure not only allows for a tight fit of the holders with the guiding mirrors, but also allows the interior to be pressurized with nitrogen to eliminate the presence of water vapor that would otherwise absorb the UV radiation. To ensure the stability of the optical path, both lasers are mounted on a common moving base.