arXiv subjects

Catherine Kealhofer

Publications and source records attributed to Catherine Kealhofer.

4 recordsLinked to original sources

arXiv2024

Angular distribution of electron emission from ultrafast nanotip sources

We investigate the angular distribution of ultrafast laser-induced electron emission from a tungsten nanotip in the multiphoton regime. A theoretical model allows precise determination of the relative contribution of different electron emission mechanisms, revealing connections between emission mechanism and the angular distribution of emitted electrons. We infer a continuous map of the work function across the surface of the tip, which in combination with the model can be used to predict values including the number of electrons per pulse and the angular divergence of the resulting beam as a function of laser power and tip voltage for (310)-oriented tungsten nanotips. The model is straightforward to implement and can be used to optimize the performance of instruments using ultrafast nanotip electron sources.

physics.app-ph↗

arXiv2015

Ultrafast time resolved photo-electric emission

The emission times of laser-triggered electrons from a sharp tungsten tip are directly characterized under ultrafast, near-infrared laser excitation at Keldysh parameters $6.6< γ< 19.1$. Emission delays up to 10 fs are observed, which are inferred from the energy gain of photoelectrons emitted into a synchronously driven microwave cavity. ~ fs timing resolution is achieved in a configuration capable of measuring timing shifts up to 55 ps. The technique can also be used to measure the microwave phase inside the cavity with a precision below 70 fs upon the energy resolved detection of a single electron.

physics.acc-ph↗

arXiv2012

Ultrafast laser-triggered emission from hafnium carbide tips

Electron emission from hafnium carbide (HfC) field emission tips induced by a sub-10 fs, 150 MHz repetition rate Ti:sapphire laser is studied. Two-photon emission is observed at low power with a moderate electric bias field applied to the tips. As the bias field and/or laser power is increased, the average current becomes dominated by thermally-enhanced field emission due to laser heating: both the low thermal conductivity of HfC and the laser's high repetition rate can lead to a temperature rise of several hundred Kelvin at the tip apex. The contribution of current from a thermal transient at times shorter than the electron-phonon coupling time is considered in the context of the two-temperature model. Under the conditions of this experiment, the integrated current from the thermal transient is shown to be negligible in comparison with the two-photon emission. A finite element model of the laser heating and thermal conduction supports these conclusions and is also used to compare the nature of thermal effects in HfC, tungsten, and gold tips.

cond-mat.mes-hall↗

arXiv2006

A spatially and temporally localized sub-laser-cycle electron source

We present an experimental and numerical study of electron emission from a sharp tungsten tip triggered by sub-8 femtosecond low power laser pulses. This process is non-linear in the laser electric field, and the non-linearity can be tuned via the DC voltage applied to the tip. Numerical simulations of this system show that electron emission takes place within less than one optical period of the exciting laser pulse, so that an 8 fsec 800 nm laser pulse is capable of producing a single electron pulse of less than 1 fsec duration. Furthermore, we find that the carrier-envelope phase dependence of the emission process is smaller than 0.1% for an 8 fsec pulse but is steeply increasing with decreasing laser pulse duration.

quant-ph↗