Direct frequency-comb spectroscopy of a dipole-forbidden clock transition in trapped 40Ca+ ions

We demonstrate direct frequency-comb (FC) spectroscopy of the dipole-forbidden 4

High-energy, high-repetition-rate picosecond pulses from a quasi-CW diode-pumped Nd:YAG system

We report on a high-power quasi-CW pumped Nd:YAG laser system, producing 130 mJ, 64 ps pulses at 1064 nm wavelength with a repetition rate of 300 Hz. Pulses from a Nd:YVO 4 oscillator are first amplified by a regenerative amplifier to the millijoule level and then further amplified in quasi-CW diode-pumped Nd:YAG modules. Pulsed diode pumping enables a high gain at repetition rates of several hundred hertz, while keeping thermal effects manageable. Birefringence compensation and multiple thermal-lensing-compensated relay-imaging stages are used to maintain a top-hat beam profile. After frequency doubling, 75 mJ pulses are obtained at 532 nm. The intensity stability is better than 1.1%, which makes this laser an attractive pump source for a high-repetition-rate optical parametric amplification system. High-energy ultrashort laser pulses are used in highharmonic generation schemes for the production of coherent radiation in the ultraviolet and soft x-ray spectral region High-energy pump pulses are generally produced in a master-oscillator power-amplifier scheme, where the generation of pulses is decoupled from the high-power amplification. Amplifier construction depends on the properties of the used gain materials, such as Nd-or Yb-doped crystals. Yb:YAG has gained a lot attention lately because of its favorable properties as a gain material. It has a high saturation fluence, and cryogenic cooling improves thermal conductivity and also transforms this medium from a quasi-three-level to a more favorable four-level system. Yb:YAG has been used in Innoslab Nd:YAG on the other hand is a well-established material that has been widely used in flashlamp-pumped cylindrical rod amplifiers. However, the repetition rate of such systems has typically been limited to the 10 Hz range In this paper we report our results on a quasi-CW diode pumped, Nd:YAG based amplification system that delivers 75 mJ, 64 ps pulses at a wavelength of 532 nm and a repetition rate of 300 Hz. For homogeneous amplification in the OPCPA, and to maximize energy extraction, a tophat beam profile is implemented. Thermal birefringence compensation is used in combination with relay imaging to generate this beam profile with a flat wavefront at 1064 nm, resulting in efficient frequency doubling after amplification. The total footprint of the laser system is less than 1.8 m 2 . The setup is shown in Inside the regenerative amplifier a Nd:YAG rod is pumped with CW laser diodes. A Pockels cell is switched on at 300 Hz, for a duration of 500 ns, to keep a single pulse traveling in the cavity for amplification in 60 round trips. A 0.5 mm thick intracavity etalon stretches the pulses in the regenerative amplifier to 64 ps, to reduce the peak intensity and to match the stretched pulse length from a Ti:sapphire oscillator which will later be used to seed an OPCPA system. The 1.2 mJ output pulses of the regenerative amplifier are amplified in two modules from the REA-series August 15, 2013 / Vol. 38, No. 16 / OPTICS LETTERS 3021 0146-9592/13/163021-03$15.00/

Direct frequency comb spectroscopy in trapped 40Ca+ ions on a dipoleforbidden clock transition

Optical frequency combs (FCs) have revolutionised ultra-high precision metrology by providing a link between optical and microwave frequencies [1]. While FCs are traditionally used for calibrating a CW probe-laser, also direct frequency comb spectroscopy (DFCS) is possible. We have recently demonstrated the versatility of DFCS performed in the environment of an ion trap, combining the broad spectral range of a Ti:sapphire FC with the feasibility of trapping and (sympathetic) cooling of different ion species [2]

Ramsey-comb spectroscopy with intense ultrashort laser pulses

Optical frequency combs based on mode-locked lasers have revolutionized the field of metrology and precision spectroscopy by providing precisely calibrated optical frequencies and coherent pulse trains. Amplification of the pulsed output from these lasers is very desirable, as nonlinear processes can then be used to cover a much wider range of transitions and wavelengths for ultra-high precision, direct frequency comb spectroscopy. Therefore full repetition rate laser amplifiers and enhancement resonators have been employed to produce up to microjoule-level pulse energies. Here we present a spectroscopic method to obtain frequency comb accuracy and resolution by using only two frequency comb pulses amplified to the millijoule pulse energy level, orders of magnitude more energetic than what has previously been possible. The new properties of this approach, such as cancellation of optical light-shift effects, are demonstrated on weak two-photon transitions in atomic rubidium and caesium, thereby improving the frequency accuracy by up to thirty times