Custom High-Resolution UV Laser Systems for new Accurate Ozone Absorption Cross Section measurements in the Huggins bands

Accurate and traceable observation of atmospheric ozone is a fundamental requirement for reliable analyses of climate evolution, air quality, and ultraviolet radiation exposure, as ozone simultaneously limits biologically harmful UV radiation and contributes to radiative forcing. Detecting and interpreting long-term ozone variability and trends requires spectroscopic inputs with high accuracy. However, ozone absorption cross sections in the UV Huggins bands (310–360 nm), used by ground-based lidars, Brewer and Dobson spectrometers, and UV-visible satellite instruments, remain a major source of uncertainty. It has been established that recommended and widely used datasets in this spectral region exhibit uncertainties exceeding 1 % at room temperature and rising above 3 % at low stratospheric temperatures. These inconsistencies introduce systematic biases when measurements from multiple platforms are combined. To address this limitation, a dedicated laser-based experimental approach was developed to determine ozone absorption cross sections with high spectral resolution and accurate frequency control across a significant part of the Huggins bands. Because continuous-wave UV laser sources are not commercially available in this wavelength range, ultraviolet radiation was produced through frequency doubling of tunable visible lasers derived from fiber-based infrared systems. These lasers were specifically designed and built for this experiment, providing narrow linewidths, stable tuning, and performance tailored to high-precision ozone spectroscopy. Two complementary laser systems were implemented: one operating between 307.8 and 308.2 nm, targeting wavelengths relevant for stratospheric lidar applications, and a second system covering 308–318 nm to match the spectral requirements of Brewer and Dobson spectrometers as well as satellite instruments. The experimental setup includes a purpose-built absorption cell that allows measurements over a controlled temperature range from −80 °C to +30 °C, thereby reproducing atmospheric conditions encountered from the ground to the lower stratosphere. Ozone used in the experiments is generated on site and has a purity of 99.8 %. In connection with simultaneous ozone measurements at 254 nm, this ensures traceability to the photometric ozone standard and minimizes contamination effects. The use of custom high-resolution laser sources and a temperature-controlled measurement cell significantly reduces biases associated with conventional broadband UV spectroscopy. The developed methodology provides a robust framework for improving existing ozone absorption datasets and for harmonizing measurements across different observing platforms.