Marina Gertsvolf

Transient nanoplasmonics inside dielectrics

Intense ultrashort light pulses interacting inside dielectrics can create nanoplasmas due to localized inhomogeneous nonlinear ionization. These nanoplasmas are bound inside the dielectric and are transient as their density changes during the light pulse—from underdense to quasi-metallic plasma densities. Interaction of light at the transient plasma–dielectric interface can lead to local field enhancements, similar to that observed in the metal-dielectric interface, which control the growth of nanoplasmas. We discuss the differences in the interaction of light at these two interfaces and demonstrate that transient nanoplasmonics can imprint periodic nanostructures inside the dielectric.

Demonstration of attosecond ionization dynamics inside transparent solids

Attosecond science has arisen from intense light pulses interacting with low density gases. We show that the initiating process—sub-cycle ionization—also survives in large band gap condensed media. Using fused SiO2 as an example, we measure the differential nonlinear absorption between the major and minor axis of elliptically polarized light. Through simulations that include ionization and light propagation, we confirm that changes in the ellipticity between the incident beam and the transmitted beam encode sub-cycle absorption dynamics. As the pulse duration is increased, we observe that sub-cycle ionization is masked by collisional processes. We propose a general class of methods for measuring attosecond dynamics in condensed media.

Self-controlled formation of microlenses by optical breakdown inside wide-band-gap materials

By repeatedly illuminating fused silica slabs with focused femtosecond pulses, we permanently decrease the local refractive index without increasing the linear absorption or scattering. This progressively forms a biconvex lens in the prefocal region. With linearly polarized light, the index change reaches several percent and is associated with the formation of an array of planar nanocracks. We analyze the polarization-dependent focusing power of the subwavelength periodic structure. While the detailed material modification changes, spontaneous defocusing lens formation is a common feature of every wide-band-gap transparent materials that we have studied (SiO2, BK7, LiF, sapphire, and mica).

An STM for molecules and wide-bandgap crystal

We are all influenced by Nicolai Delone’s research. Through much of his career, his influence reached Canada through his published papers. However, Professor Delone visited the National Research Council of Canada’s laboratories at least three times from about 1989 to 1995. At that time he was primarily interested in stabilization. Stabilization refers to the fact that, as the intensity of laser light illuminating an atom is increased, the ionization rate passes through a maximum, then falls. Surprisingly the atom becomes stable against ionization at very high intensities.

Mapping the magnetic field vector in a fountain clock

We show how the mapping of the magnetic field vector components can be achieved in a fountain clock by measuring the Larmor transition frequency in atoms that are used as a spatial probe. We control two vector components of the magnetic field and apply audio frequency magnetic pulses to localize and measure the field vector through Zeeman spectroscopy.

Status of the atomic fountain clock at the National Research Council of Canada

Despite the rapid advances in optical frequency standards, caesium fountain clocks retain a critical role as the most accurate primary frequency standards available. At the National Research Council Canada, we are working to develop a second generation caesium fountain clock. Work is currently underway to improve several systems of FCs1, such as the laser system and microwave local oscillator, which will be incorporated into its refurbished version, FCs2. In addition, we have added an optical pumping stage which has increased the detected atom number by over a factor of six. In collaboration with the National Physical Laboratory (NPL), we are planning on replacing the physics package of FCs1. We will report on several recent improvements to FCs1, along with our progress in the development of FCs2.

High refractive index modification of SiO2 created by femtosecond laser nanostructuring

By comparing simulations with experiment, we show that the effective refractive index of fused SiO2 can be locally reduced by (1.8 ? 0.2)% by femtosecond laser nanostructuring. We create a microlens of material containing a planar array of nanocracks embedded inside fused silica and probe how it refracts or absorbs light as a function of pulse energy. The self-generated microlens lowers the peak light intensity by deflecting the light around the focus. We obtain the refractive index by simulating the beam transport using the 3D wave equation in conjunction with the measured dimensions of the modified material.

Evaluation of NRC-FCs1: Mapping the C-field using the Larmor frequency

An uncertainty evaluation of NRCs cesium fountain clock FCs1 is currently being performed. One task of this evaluation consists in quantifying the contribution to the frequency uncertainty, the second-order Zeeman shift. We report the results obtained from measurements of the C-field above the Ramsey cavity using the Larmor frequency as a probe. This technique is possible because a transverse C-field is used in NRC-FCs1 and alignment electrodes are available to produce an orthogonal excitation field. The non-uniformity of the C-field near the Ramsey cavity and the uncertainties in the measurements produce the largest contribution to the type-B uncertainty.

From carrier dynamics inside fused silica to control of multiphoton-avalanche ionization for laser machining

Using pump-probe measurements, we characterize carrier decay time inside fused silica and measure deeply bound self-trapped excitons. With pump-probe delay, we also control free carrier injection and the subsequent avalanche process for laser machining applications.

Polarization Dependence of Nanostructure Formation in Transparent Solids

We demonstrate how the polarization of light controls the geometry of nanostructures formed by ultrashort laser pulses in fused quartz.