Michael Gerrity

Phase matching of high harmonic generation in the soft and hard X-ray regions of the spectrum

We show how bright, tabletop, fully coherent hard X-ray beams can be generated through nonlinear upconversion of femtosecond laser light. By driving the high-order harmonic generation process using longer-wavelength midinfrared light, we show that, in theory, fully phase-matched frequency upconversion can extend into the hard X-ray region of the spectrum. We verify our scaling predictions experimentally by demonstrating phase matching in the soft X-ray region of the spectrum around 330 eV, using ultrafast driving laser pulses at 1.3-μm wavelength, in an extended, high-pressure, weakly ionized gas medium. We also show through calculations that scaling of the overall conversion efficiency is surprisingly favorable as the wavelength of the driving laser is increased, making tabletop, fully coherent, multi-keV X-ray sources feasible. The rapidly decreasing microscopic single-atom yield, predicted for harmonics driven by longer-wavelength lasers, is compensated macroscopically by an increased optimal pressure for phase matching and a rapidly decreasing reabsorption of the generated X-rays.

Bright, Coherent, Ultrafast Soft X-Ray Harmonics Spanning the Water Window from a Tabletop Light Source

We demonstrate fully phase-matched high harmonic emission spanning the water window spectral region important for nano- and bioimaging and a breadth of materials and molecular dynamics studies. We also generate the broadest bright coherent bandwidth (≈300  eV) to date from any light source, small or large, that is consistent with a single subfemtosecond burst. The harmonic photon flux at 0.5 keV is 10³ higher than demonstrated previously. This work extends bright, spatially coherent, attosecond pulses into the soft x-ray region for the first time.

2D IR spectroscopy at 100 kHz utilizing a Mid-IR OPCPA laser source.

We present a 100 kHz 2D IR spectrometer. The system utilizes a ytterbium all normal dispersion fiber oscillator as a common source for the pump and seed beams of a MgO:PPLN OPCPA. The 1030 nm OPCPA pump is generated by amplification of the oscillator in cryocooled Yb:YAG amplifiers, while the 1.68 μm seed is generated in a OPO pumped by the oscillator. The OPCPA outputs are used in a ZGP DFG stage to generate 4.65 μm pulses. A mid-IR pulse shaper delivers pulse pairs to a 2D IR spectrometer allowing for data collection at 100 kHz.

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.

Sub-wavelength transmission and reflection mode tabletop imaging with 13nm illumination via ptychography CDI

EUV lithography is promising for addressing upcoming, <10nm nodes for the semiconductor industry, but with this promise comes the need for reliable metrology techniques. In particular, there is a need for actinic mask inspection in which the imaging wavelength matches that of the intended lithography process, so that the most relevant defects are detected. Here, we demonstrate tabletop, ptychographic, coherent diffraction imaging (CDI) in reflection- and transmission-modes of extended samples, using a 13 nm high harmonic generation (HHG) source. We achieve the first sub-wavelength resolution EUV image (0.9λ) in transmission, the highest spatial resolution using any 13.5 nm source to date. We also present the first reflection-mode image obtained on a tabletop using 12.7 nm light. This work represents the first 12.7 nm reflection-mode image using any source of a general sample.

Wide Field-of-View Reflection-Mode Ptychographic Imaging Microscope with Tabletop 12.7 nm High Harmonic Illumination

High-resolution imaging is an invaluable tool for understanding nanoscale systems. In particular, tabletop extreme ultraviolet (EUV) coherent diffractive imaging (CDI) techniques based on high harmonic generation (HHG) can combine femtosecond (fs) pulse durations with nanometer resolution and elemental-, spin-, electronicand magnetic-sensitivity, proving to be an ideal probe of complex nanostructured systems [1-2]. In this work, we demonstrate a novel technique for glancing-incidence, large field-of-view, reflection-mode ptychographic imaging using a tabletop 12.7nm HHG source. To our knowledge, this is the first demonstration of reflection-mode imaging at 12.7nm on a tabletop, as well as the first ~13nm reflection-mode image using any source of an extended sample of general composition (ie., not fabricated on a multilayer mirror).

High Peak and Average Power Near/Mid-IR Femtosecond Laser Sources

I will present work on hybrid fiber/bulk systems employing non-linear amplifiers to reach near and mid-IR wavelengths to obtain high peak and average powers, with <100 femtosecond pulse durations. These systems have a wide range of uses from biotech imaging techniques, hard X-ray generation, and industrial/medical micromachining. I will illustrate our specific designs for pushing the limits on femtosecond fiber laser technology, mating it with solid state lasers, and extending these systems to meet the needs of cutting edge science.

Multi-mJ, High Repetition Rate, mid-IR OPCPA System

We present a multi-mJ, 1 kHz repetition-rate, mid-IR OPCPA laser, for soft x-ray high harmonic generation. To date we have demonstrated 2.7mJ at 1.6µm, and 1.1mJ at 3µm, with sufficient bandwidth in each to support <100fs compression.

Practical Compact Spatially-Coherent, Phase-Matched Extreme UV Source at 50 kHz

We report the first efficient source of spatially-coherent extreme-UV light at the high repetition rates (>50kHz) needed for metrology and imaging applications. This practical compact tabletop EUV source uses IR pulse energy of only 25μJ.