Brookhaven Lecture

The molecular-gas CO2 laser was invented in 1964, at the very beginning of the laser era. Due to its high efficiency, robustness, and scalability, it quickly became a first-choice laser for science, industry, and defense. Development of new types of solid-state lasers and the invention of chirped-pulse amplification in the 1980s led to a gradual decrease in the number of CO2 laser systems deployed. The unique 10-micron wavelength in the long-wave infrared (LWIR), however, makes CO2 lasers indispensable in specific applications and stimulates the development of new generations of these amazing machines. High-energy physics, and, in particular, laser acceleration of charged particles, are among the fields in which high-power, long-wave infrared laser sources are highly desirable. To address this need, in 1997, the BNL Accelerator Test Facility (ATF) deployed a high-pressure CO2 laser system, which has now undergone a series of upgrades. The ATF's LWIR laser enabled a number of "first-ever" experiments that included the inverse free-electron laser acceleration, inverse Cherenkov acceleration, staged laser acceleration, and monoenergetic ion acceleration from a gas target. A large team of researchers from several world-renowned institutions is presently collaborating to reach a breakthrough in laser wakefield acceleration (LWFA). This high-gradient acceleration scheme is believed to have the potential to revolutionize particle acceleration technology by enabling the production of high-energy table-top accelerators. Wavelength scaling of the underlying physical processes results in accelerating plasma structures that are orders of magnitude larger and with much higher charges when a 10-micron LWIR laser is used to create them than those produced by conventional solid-state laser systems operating at 1-micron wavelength. The success of the development and scale-up of new laser acceleration schemes such as LWFA strongly depend on the availability of lasers that satisfy highly challenging requirements. These requirements are pushing the LWIR laser research and development effort at ATF. In recent years, ATF has implemented several approaches unique to gas lasers in its LWIR system. These include isotopically enriched CO2 active medium, chirped-pulse amplification and the use of a low-energy, solid-state front end for seeding the CO2 power amplifiers. Presently, the laser delivers 5 TW peak power in a 14 J, 2 ps pulse, which is the shortest multi-terawatt LWIR laser pulse ever achieved. Ongoing development of a millijoule-class frontend laser will allow reducing the pulse duration to 500 fs via the use of two branches, instead of one, of the CO2 gain spectrum. This will increase the system peak power to the 10–15 TW required by the next-generation LWFA experiments. The next ambitious goal is the post-compression of the pulse to between 100 and 200 fs (which is very short, considering that the duration of the optical cycle at 10 um is 33 fs) and the achievement of 20+ TW peak power, which will enable laser acceleration of ions to energy levels sufficient for some medical applications. Our very recent demonstration of the compression of a sub-terawatt 2 ps pulse to