K. D. Moll

100 MHz frequency combs in the XUV spectral region

High-harmonic generation is achieved at 100 MHz repetition rates by utilizing a femtosecond enhancement cavity to increase peak intensities from a mode-locked laser. This provides a coherent frequency comb in the VUV for high-resolution spectroscopy.

Toward Direct Frequency Comb Spectroscopy in Helium: Proposed Measurements and Experimental Progress

We describe progress toward precision measurements in helium by direct use of a phase-stabilized frequency comb, including numerical calculations of estimated signal sizes and lineshapes, and experimental work on a bichromatic-force slower for metastable helium.

Self-focusing and multiple filamentation of intense laser pulses

We show experimentally that the spatial profile of a collapsing beam evolves to the circularly symmetric Townes profile. We also show deterministic methods for controlling multiple filamentation of high-power pulses. The basic model for propagation of intense laser beams in a bulk Kerr medium is given by the dimensionless 2D nonlinear Schrödinger equation (NLS) 2 ( , , ) 0. z xx yy i x y z A A A A A + + + = Here A is the amplitude of the electric field, z is the propagation direction, and x and y are the transverse directions. The NLS has waveguide solutions of the A(z,r) = a exp(i a z) R(ar), where r = (x+y), and R, the so-called Townes profile, is the ground-state solution of the equation

PRECISION MEASUREMENT MEETS ULTRAFAST CONTROL

Optical spectroscopy and frequency metrology at the highest level of precision and resolution are being greatly facilitated by the use of ultracold atoms and phase stabilized light in the form of both cw and ultrashort pulses. It is now possible to pursue simultaneously coherent control of quantum dynamics in the time domain and high precision measurements of global atomic structure in the frequency domain. These coherent light-based precision measurement capabilities may be extended to the XUV spectral region, where new possibilities and challenges lie for precise tests of fundamental physical principles.

Observation of self-similar nonlinear wave collapse

We show that during self-focusing induced collapse of a laser beam, the spatial profile evolves into the same cylindrically symmetric shape, known as the Townes soliton, regardless of the shape of the input beam profile.

Self-focusing dynamics and catastrophic collapse of ultrashort laser pulses

Summary form only given. We study the nonlinear dynamical behavior of the self-focusing of femtosecond pulses both near and above the point at which the pulse effectively undergoes catastrophic collapse. Even for pulses substantially longer than a single optical cycle, our results indicate that the dynamics can only be described by a model that goes beyond the slowly-varying envelope approximation.