Direct optical field sampling

Characterizing few-cycle UV resonant dispersive waves through direct field sampling

We demonstrate compression of few-cycle ultraviolet (UV) resonant dispersive waves (RDWs) generated in a cascaded hollow capillary fiber setup using a Yb laser system. Temporal characterization is performed using both tunneling ionization with a perturbation for the time-domain observation of an electric field (TIPTOE) and self-diffraction frequency resolved optical gating (SD-FROG), which show good agreement. Through careful dispersion management, we compress the RDW pulse to 6.9~fs at a $\sim$390~nm central wavelength. This is to our knowledge the first measurement of an RDW using the TIPTOE method and demonstrates the viability of this technique to reliably characterize few-cycle UV pulses with $\mu$J pulse energies.

The cascaded hollow capillary fiber (HCF) set-up and Yb laser beam path is depicted below.

A schematic depicting the cascaded HCF system used to generate RDWs. The spectrum of the pulse at each successive fiber entrance are enumerated and displayed at the top of the figure (1-3), in addition to the output spectrum from the RDW/soliton generation stage (4). L - lens, CM - chirped mirrors, SCM - spherical concave mirror, W - wedge pair, $\lambda$/2 - half wave plate, P - wire grid polarizer, DM - dichroic mirrors (unlabeled mirrors are high reflectors).

The parameters for the RDW/soliton generation fiber are presented below, in addition to some exemplary spectra.

Spectra as a function of gas pressure for the RDW/soliton hollow capillary fiber.

The tunability of the RDW is illustrated by simply changing gas pressure and gas species in the hollow capillary fiber, providing spectral coverage from 195 - 450 nm.

Various RDW spectra taken at different gas pressures and using different gas species.

The RDW pulse is characterized using SD-FROG, where the retrieval is shown below.

SD-FROG retrieval, indicating a pulse duration of 6.9 fs.

The RDW pulse is also characterized using direct optical field sampling (TIPTOE), where the result is shown below.

Direct field sampling measurement of the RDW pulse.

Finally, we can compare these two methods and we see there is close agreement.

Comparing SD-FROG with direct field sampling.