Daniel Kolbe

Continuous-wave Lyman-alpha generation with solid-state lasers

A coherent continuous-wave Lyman-alpha source based on four-wave sum-frequency mixing in mercury vapor has been realized with solid-state lasers. The third-order nonlinear susceptibility is enhanced by the 6(1)S - 7(1)S two-photon resonance and the near 6(1)S-6(3)P one-photon resonance. The phase matching curve for this four-wave mixing scheme is observed for the first time. In addition we investigate the two-photon enhancement of the Lyman-alpha yield and observe that the maxima of Lyman-alpha generation are shifted compared to the two-photon resonances of the different isotopes.

4W continuous-wave narrow-linewidth tunable solid-state laser source at 546nm by externally frequency doubling a ytterbium-doped single-mode fiber laser system.

A high-power continuous-wave coherent light source at 545.5nm is described. We use 8.3W from a solid-state ytterbium-doped single-mode fiber oscillator/amplifier system as input into an external frequency doubling stage. This system produces up to 4.1W of stable green single-frequency laser radiation. We characterize the light source by performing absorption spectroscopy on iodine across the full tuning range of the fiber laser and saturation spectroscopy on one strong iodine line of the doppler-broadened spectrum.

A continuous wave 10 W cryogenic fiber amplifier at 1015 nm and frequency quadrupling to 254 nm

A stable, continuous wave, single frequency fiber amplifier system at 1015 nm with 10 W output power is presented. It is based on a large mode double clad fiber cooled to liquid nitrogen temperature. The amplified light is frequency quadrupled to 254 nm and used for spectroscopy of the 6¹S → 6³P transition in mercury.

Triple resonant four-wave mixing boosts the yield of continuous coherent vacuum ultraviolet generation.

Efficient continuous-wave four-wave mixing by using three different fundamental wavelengths with individual detunings to resonances of the nonlinear medium is shown. Up to 6 μW of vacuum ultraviolet light at 121 nm can be generated, which corresponds to an increase of three orders of magnitude in efficiency. This opens the field of quantum information processing by Rydberg entanglement of trapped ions.

Continuous-wave, double-pass second-harmonic generation with 60% efficiency in a single MgO:PPSLT crystal

We present a double-pass scheme for high-efficiency, high-power, second-harmonic generation (SHG) in a single MgO-doped periodically poled stoichiometric lithium tantalate (MgO:PPSLT) crystal. The device is pumped by a single-frequency, continuous-wave fiber amplifier laser system at a wavelength of 1091 nm. For the double-pass scheme, a conversion efficiency of 60% and a harmonic power of 12.8 W at a wavelength of 545.5 nm with a high beam quality of (M2<1.2) is achieved. Compared to single-pass SHG, a double-pass enhancement factor of more than two is observed at the highest fundamental pump power.

Rydberg Excitation of a Single Trapped Ion.

We demonstrate excitation of a single trapped cold (40)Ca(+) ion to Rydberg levels by laser radiation in the vacuum ultraviolet at a wavelength of 122 nm. Observed resonances are identified as 3d(2)D(3/2) to 51F, 52F and 3d(2)D(5/2) to 64F. We model the line shape and our results imply a large state-dependent coupling to the trapping potential. Rydberg ions are of great interest for future applications in quantum computing and simulation, in which large dipolar interactions are combined with the superb experimental control offered by Paul traps.

A semiconductor laser system for the production of antihydrogen

Laser-controlled charge exchange is a promising method for producing cold antihydrogen. Caesium atoms in Rydberg states collide with positrons and create positronium. These positronium atoms then interact with antiprotons, forming antihydrogen. Laser excitation of the caesium atoms is essential to increase the cross section of the charge-exchange collisions. This method was demonstrated in 2004 by the ATRAP collaboration by using an available copper vapour laser. For a second generation of charge-exchange experiments we have designed a new semiconductor laser system that features several improvements compared to the copper vapour laser. We describe this new laser system and show the results from the excitation of caesium atoms to Rydberg states within the strong magnetic fields in the ATRAP apparatus.

Continuous-wave spontaneous lasing in mercury pumped by resonant two-photon absorption

We demonstrate the first cw two-photon absorption laser-induced stimulated emission. The 7(1)S(0)-6(1)P(1) transition in mercury at a 1014 nm wavelength is used, and selective lasing of different isotopes is observed.

A reliable cw Lyman-α laser source for future cooling of antihydrogen

We demonstrate a reliable continuous-wave (cw) laser source at the 1 S–2 P transition in (anti)hydrogen at 121.56 nm (Lyman-α) based on four-wave sum-frequency mixing in mercury. A two-photon resonance in the four-wave mixing scheme is essential for a powerful cw Lyman-α source and is well investigated.

Triple resonant four-wave mixing: A microwatt continuous-wave laser source in the vacuum ultraviolet region at 120 nm

We present a vacuum ultraviolet laser source by four-wave mixing in mercury vapour based on solid-state laser systems. Maximum powers of 6μW were achieved with an increase of four orders of magnitude in efficiency.