Removing tattoos with lasers is tricky business as surgeons be very cautious to ensure the skin is not overheated as that would result in scarring. The normal procedure involves using a coolant such as tetrafluoroethane which reduces skin temperature as it evaporates. Tetrafluoroethane has one unfortunate property: it contributes to greenhouse gases as it is many times worse than carbon dioxide.
Taking that into consideration, John Stuart Nelson at the the Beckman Laser Institute (University of California) developed and patented an alternative removal method which uses pressurised liquid CO2 (carbon dioxide) as the cooling agent. It is delivered as a fine mist of solid dry ice particles which reduce skin temperatures before sublimating into a gaseous form.