Margaret M. Murnane

Time-domain classification of charge-density-wave insulators

Distinguishing insulators by the dominant type of interaction is a central problem in condensed matter physics. Basic models include the Bloch-Wilson and the Peierls insulator due to electron-lattice interactions, the Mott and the excitonic insulator caused by electron-electron interactions, and the Anderson insulator arising from electron-impurity interactions. In real materials, however, all the interactions are simultaneously present so that classification is often not straightforward. Here, we show that time- and angle-resolved photoemission spectroscopy can directly measure the melting times of electronic order parameters and thus identify-via systematic temporal discrimination of elementary electronic and structural processes-the dominant interaction. Specifically, we resolve the debates about the nature of two peculiar charge-density-wave states in the family of transition-metal dichalcogenides, and show that Rb intercalated 1T-TaS(2) is a Peierls insulator and that the ultrafast response of 1T-TiSe(2) is highly suggestive of an excitonic insulator.

Attosecond Coherent Control of Single and Double Photoionization in Argon

Ultrafast high harmonic beams provide new opportunities for coherently controlling excitation and ionization processes in atoms, molecules, and materials on attosecond time scales by employing multiphoton two-pathway electron-wave-packet quantum interferences. Here we use spectrally tailored and frequency tuned vacuum and extreme ultraviolet harmonic combs, together with two phase-locked infrared laser fields, to show how the total single and double photoionization yields of argon can be coherently modulated by controlling the relative phases of both optical and electronic-wave-packet quantum interferences. This Letter is the first to apply quantum control techniques to double photoionization, which is a fundamental process where a single, high-energy photon ionizes two electrons simultaneously from an atom.

Grism Based Stretcher/Compressor System for Amplified, Femtosecond Kilohertz Lasers

We demonstrate a simple and efficient grism based stretcher/compression system. 40 fs, 300 µJ pulses are generated at 5 kHz using this unique amplifier design.

Generation of megaelectronvolt electron beams by an ultrashort (<30 fs), intense laser pulse

Ultrafast, megaelectronvolt electron beams with a divergence angle as small as 1° have been generated by an ultrashort (<30 fs), intense laser pulse. The experimental phenomena, related physics, and the development of such an e-source at 1 KHz repetition rate are described.

Complex EUV imaging reflectometry: spatially resolved 3D composition determination and dopant profiling with a tabletop 13nm source

With increasingly 3D devices becoming the norm, there is a growing need in the semiconductor industry and in materials science for high spatial resolution, non-destructive metrology techniques capable of determining depth-dependent composition information on devices. We present a solution to this problem using ptychographic coherent diffractive imaging (CDI) implemented using a commercially available, tabletop 13 nm source. We present the design, simulations, and preliminary results from our new complex EUV imaging reflectometer, which uses coherent 13 nm light produced by tabletop high harmonic generation. This tool is capable of determining spatially-resolved composition vs. depth profiles for samples by recording ptychographic images at multiple incidence angles. By harnessing phase measurements, we can locally and nondestructively determine quantities such as device and thin film layer thicknesses, surface roughness, interface quality, and dopant concentration profiles. Using this advanced imaging reflectometer, we can quantitatively characterize materials-sciencerelevant and industry-relevant nanostructures for a wide variety of applications, spanning from defect and overlay metrology to the development and optimization of nano-enhanced thermoelectric or spintronic devices.

Prototype through-pellicle coherent imaging using a 30nm tabletop EUV source

We present preliminary through-pellicle imaging using a 30nm tabletop extreme ultraviolet (EUV) coherent diffractive imaging microscope. We show that even in a non-optimized setup, this technique enables through-pellicle imaging of a sample with no detectable impact on image fidelity or resolution.

Nanoscale surface phononic crystals for characterization of complex and periodic materials using extreme ultraviolet light

Phononic crystals and acoustic metamaterials enable the precise control of elastic properties, even in ranges inaccessible to traditional materials, making them useful for applications ranging from acoustic waveguiding to thermoelectrics. In particular, surface phononic crystals (SPCs) consisting of periodic nanolines on a semi-infinite substrate can be used to generate narrow bandwidth pseudosurface acoustic waves with exquisite sensitivity to the elastic properties of the underlying substrate. Tuning the period of the surface phononic crystal tunes the penetration depth of the pseudosurface wave, and thus selectively probes different depths of layered substrates. In our experiments, we use ultrafast near infrared laser pulses to excite these waves in the hypersonic frequency range by illuminating absorbing metallic nanolines fabricated on top of complex substrates. We probe the nanoscale dynamics launched by our SPCs via pump-probe spectroscopy where we monitor the diffraction of ultrafast pulses of extreme ultraviolet light generated via tabletop high harmonic generation. We then extract the mechanical properties of the substrate by comparing our measurements to quantitative finite element analysis. Utilizing this technique, we characterize the effective elastic and thermal transport properties of 3D periodic semiconductor metalattices.

0.5 MHz 50fs ?J-class Ultrafast Laser Amplifier System

We report an innovative and robust ultrafast Ti:sapphire regenerative amplifier system accessing a new operating regime tunable from 50kHz up to 500kHz-repetition-rate, up to 10?J, 50fs pulses, enabling applications in micromachining, imaging, and spectroscopy.

Efficient 100 kHz-Repetition-Rate Ultrafast Laser System with OPA/NOPA Frequency Conversion

We report an innovative ultrafast Ti:Sapphire laser-amplifier/OPA/NOPA system accessing a new operating regime of 30% efficient, tunable, 100kHz-repetition-rate, 20μJ, 50fs pulses, enabling applications in micromachining, imaging, and spectroscopy. Millijoule pulses are attainable using cryogenic cooling.

Manipulating Attosecond Electrons for Coherent X-Ray Generation from Atoms and Molecules

We demonstrate phase matching in the soft-x-ray region using trains of counterpropagating light pulses, by manipulating electron dynamics on the fastest, attosecond, time-scales. We enhance the x-ray output by almost 1000. Article not available.