Compact solid-state laser source for1S−2Sspectroscopy in atomic hydrogen

We demonstrate a compact solid-state laser source for high-resolution two-photon spectroscopy of the $1S\text{−}2S$ transition in atomic hydrogen. The source emits up to $20\mathrm{mW}$ at $243\mathrm{nm}$ and consists of a $972\mathrm{nm}$ diode laser, a tapered amplifier, and two doubling stages. The diode laser is actively stabilized to a high-finesse cavity. We compare the new source to the stable $486\mathrm{nm}$ dye laser used in previous experiments and record $1S\text{−}2S$ spectra using both systems. With the solid-state laser system, we demonstrate a resolution of the hydrogen spectrometer of $6\times {10}^{11}$, which is promising for a number of high-precision measurements in hydrogenlike systems.