Today the pulsed CO₂ laser is used in applications such as paint stripping, spectroscopy, non-destructive testing, LIDAR, and laser photochemistry. In general, these applications require wavelength tuneability and/or narrow bandwidth operation.

The CO₂ laser is a molecular laser, and the energy levels of concern are the rotational and vibrational levels of the CO₂ molecule. Tunability is achieved by operating the laser on different vibrational levels. This can be achieved by inserting a wavelength selective element, such as a diffraction grating, inside the cavity.

Depending on the vibrational transition selected, the laser can be operated in either the 9μm or 10μm regions. Usually a TEA CO₂ laser is line tunable. This means that the laser can only be operated on discrete lines, with no wavelength selection between the lines. However, by increasing the operating pressure, continuous tunability can be achieved, i.e., you could operate at wavelengths that are between the discrete lines.

At SDILasers, we offer a full range of pulsed line tuneable and continuously tuneable CO₂ lasers.

The typical bandwidth of an atmospheric CO₂ laser is approximately 300MHz. This means that at least three longitudinal modes are lasing simultaneously. To decrease the bandwidth, SDILasers can make use of injection mode locking, intracavity etalons, or low gain cells.

Injection mode locking is the most versatile but as can be seen from the image below, minimum seed intensity is required to ensure single mode operation.

Single Longitudinal Mode (SLM) operation is characterised by a smooth temporal pulse. If only narrow bandwidth operation is required, then a high-pressure laser with grazing incidence grating can be used. This will narrow the bandwidth of the laser to approximately 300 MHz.

The figure below shows a single longitudinal mode pulse, generated by a WH-20 laser that has been injection locked with a low-pressure stabilized cw CO₂ laser.

Short Pulse Amplification
One advantage of high-pressure lasers is that because their gain spectrum is so wide, they can be used to amplify large bandwidth pulses.  The ability to amplify large bandwidth pulses makes this type of laser particularly useful for the amplification of IR ultra-short pulses as shown by this picture of a multi-pass 10Bar amplifier installed at Brookhaven National Laboratory.