David Kielpinski

Isotope selective optical excitation of atoms is important for experiments with neutral atoms, metrology, and work with trapped ions, including quantum information processing. Polarization-enhanced absorption spectroscopy is used to frequency stabilize a tunable external cavity laser diode system at 398.9 nm for isotope selective photoionization of neutral Yb atoms. This spectroscopy technique is used to measure isotope resolved dispersive features from transitions within a see-through configuration ytterbium hollow-cathode discharge lamp. This Doppler-free dichroic polarization spectroscopy is realized by retro-reflecting a laser beam through the discharge and analyzing the polarization dependent absorption with balanced detection. The spectroscopy signal is recovered using lock-in detection of frequency modulation induced by current modulation of the external cavity laser diode. Here, we show an order of magnitude improvement in the long-term stability using polarization-enhanced absorption spectroscopy of Yb compared to polarization spectroscopy.

Ionization of atoms and molecules in strong laser fields is a fundamental process in many fields of research, especially in the emerging field of attosecond science. So far, demonstrably accurate data have only been acquired for atomic hydrogen (H), a species that is accessible to few investigators. Here, we present measurements of the ionization yield for argon, krypton, and xenon with percent-level accuracy, calibrated using H, in a laser regime widely used in attosecond science. We derive a transferable calibration standard for laser peak intensity, accurate to 1.3%, that is based on a simple reference curve. In addition, our measurements provide a much needed benchmark for testing models of ionization in noble-gas atoms, such as the widely employed single-active electron approximation.

Ionization of atoms and molecules in strong laser fields is a fundamental process in many fields of research, especially in the emerging field of attosecond science. So far, demonstrably accurate data have only been acquired for atomic hydrogen (H), a species that is accessible to few investigators. Here we present measurements of the ionization yield for argon, krypton, and xenon with percentlevel accuracy, calibrated using H, in a laser regime widely used in attosecond science. We derive a transferrable calibration standard for laser peak intensity, accurate to 1.3%, that is based on a simple reference curve. In addition, our measurements provide a much-needed benchmark for testing models of ionisation in noble-gas atoms, such as the widely employed single-active electron approximation.

We present percent-level accurate ionisation yields of atomic hydrogen, argon, krypton, and xenon by few-cycle lasers. From these measurements, a peak laser intensity calibration standard is derived, accurate to 1.3% in the 10¹⁴ W/cm² regime.

We explore the effect of nuclear mass on the laser-driven electron localization process. We dissociate a mixed H${}_{2}$ and D${}_{2}$ target with intense, carrier-envelope-phase (CEP) stable 6 fs laser pulses and detect the products in a reaction microscope. We observe a very strong CEP-dependent asymmetry in proton and deuteron emission for low dissociation energy channels. This asymmetry is stronger for H${}_{2}$ than for D${}_{2}$. We also observe a large CEP offset between the asymmetry spectra for H${}_{2}$ and D${}_{2}$. Our theoretical simulations, based on a one-dimensional two-channel model, agree very well with the asymmetry spectra, but fail to account properly for the phase difference between the two isotopes.

We present the measured photoionization yield of atomic hydrogen as a function of laser intensity for few-cycle pulses. Fits with exact ab-initio simulations produce better agreement than analytical theories and enable accurate intensity calibration.

We experimentally optimize the yield of attosecond XUV pulses, with pulse duration inferred from carrier-envelope-phase resolved spectral measurements. We also demonstrate generation of dual attosecond pulses with timing resolution of 90 zeptoseconds.

Fluorescence from three photon absorption was observed in CdSe quantum dots excited with ultrashort pulses from a telecom band Erbium fibre laser. Reduced scattering at longer wavelengths makes this approach interesting for deep tissue imaging.