Compact solid-state laser source for $1S\text{−}2S$ spectroscopy 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.

Figure 1

A schematic diagram of the experimental setup. ECDL is the external cavity diode laser at $972\mathrm{nm}$, TA is the tapered amplifier, SHG 1,2 are the second-harmonic-generation stages, PDH represents the Pound-Drever-Hall lock, and AOM is the acousto-optic modulator used for scanning the laser frequency. The output of the stabilized dye laser at $486\mathrm{nm}$ is superimposed with the output of the SHG 1 and is used both for the beat signal detection using a radiofrequency (RF) spectrum analyzer and for generation of $243\mathrm{nm}$ radiation. The hydrogen spectra are detected alternatively either using the dye laser or the solid-state system.

Figure 2

Power spectrum of the beat note at $486\mathrm{nm}$ between the second harmonic of the diode laser and the dye laser in a logarithmic scale. Inset: The zoomed central part of the spectrum plotted on a linear scale. The dashed line shows a Lorentzinan fit with a $1\mathrm{kHz}$ FWHM.

Figure 3

Top: $1S\text{−}2S$ time-resolved spectra recorded with the diode laser source. The power of $243\mathrm{nm}$ radiation coupled to the enhancement cavity equals $2.6\mathrm{mW}$. Bottom: $1S\text{−}2S$ spectra recorded with the dye laser source at the power of $2.2\mathrm{mW}$. In each case, two spectra recorded in two different scan directions are averaged and the drift of the corresponding reference cavity is compensated. The plots corresponding to different delays are vertically shifted by 50, 100, and 150 counts.