Second Order Nonlinear Optics with Ultrashort Frequency Combs

Nonlinear optical frequency conversion techniques have now existed for 60 years; frequency combs have now also been important scientific tools for two decades. Nonlinear optics is a vital piece of experimental realizations of frequency combs in the form of f-2f interferometry for stabilization of the carrier envelope offset frequency. Frequency combs, owing to their unparalleled frequency stability, broad spectral bandwidths, and coherent link between microwave and optical frequencies, have similarly had an impact on the field of optical frequency conversion.The work in this thesis demonstrates the important symbiotic relationship between nonlinear optics and optical frequency combs – combs could not have existed without nonlinear optics, and combs continue to push the boundaries of what is possible in nonlinear optics. In this work, I show the generation of few-cycle pulses from Er:fiber oscillators, approaching the picture of frequency combs being delta functions in the time and frequency domain. With these ultrashort pulses, I show mid-infrared frequency comb generation with intrapulse difference frequency generation. Dual comb spectroscopy in the mid-infrared shows the applicability of these combs. I also show a novel comb stabilization technique relying on offset frequency detection in the mid-infrared. With ultrashort near-infrared pulses, I show mid-infrared comb measurement techniques using electro- optic sampling and discuss the current noise limits. Finally, this dissertation also provides an outlook on future techniques enabled by frequency combs aimed at measuring light sources beyond coherent laser frequency combs

Phenomenology of Higgs bosons in QCD at the LHC

This thesis presents two phenomenological research projects focusing on the nature of Higgs bosons in quantum chromodynamics and tool building for precision studies of the Standard Model and beyond at the Large Hadron Collider. The first project presents H1jet, a fast and easy-to-use program that computes the total cross-section and differential distribution in the transverse momentum of a colour singlet. In its current version, the program implements only leading-order 2 æ 1 and 2 æ 2 processes, but could be extended to higher orders. H1jet can be used by theorists to quickly assess deviations of selected new physics models from the Standard Model behaviour, and quickly obtain distributions of relevance for Standard Model phenomenology. The second project presents a detailed study of Higgs interference effects at next-to-leading-order in the 1-Higgs-singlet extension of the Standard Model for the process pp (æ {h1, h2}) æ tt¯+ X. The interference effects have been studied for different benchmark points with heavy Higgs masses in the range 700–3000 GeV. For this purpose, gghtt, a parton-level NLO Monte Carlo event generator, has been developed, making it possible to study the interference effect between tree-level and loop-induced processes at NLO. Future versions of gghtt can easily be generalised to work for any loop-induced process

H1jet, a fast program to compute transverse momentum distributions

We present H1jet, a fast code that computes the total cross section and differential distribution in the transverse momentum of a colour singlet. In its current version, the program implements only leading-order 2 → 1 and 2 → 2 processes, but could be extended to higher orders. We discuss the processes implemented in H1jet, give detailed instructions on how to implement new processes, and perform comparisons to existing codes. This tool, mainly designed for theorists, can be fruitfully used to assess deviations of selected new physics models from the Standard Model behaviour, as well as to quickly obtain distributions of relevance for Standard Model phenomenology

On angular momentum of gravitational radiation

The quasigroup approach to the conservation laws (Phys. Rev. D56, R7498 (1997)) is completed by imposing new gauge conditions for asymptotic symmetries. Noether charge associated with an arbitrary element of the Poincar\'e quasialgebra is free from the supertranslational ambiquity and identically vanishes in a flat spacetimeComment: Revtex4 styl

Euclidean Mahler measure and twisted links

If the twist numbers of a collection of oriented alternating link diagrams are bounded, then the Alexander polynomials of the corresponding links have bounded euclidean Mahler measure (see Definition 1.2). The converse assertion does not hold. Similarly, if a collection of oriented link diagrams, not necessarily alternating, have bounded twist numbers, then both the Jones polynomials and a parametrization of the 2-variable Homflypt polynomials of the corresponding links have bounded Mahler measure.Comment: This is the version published by Algebraic & Geometric Topology on 7 April 200

A New Model for Jet Energy Loss in Heavy Ion Collisions

We present a new model for jet quenching from coherent radiation in a brick medium. The jet energy loss is simulated as a perturbative final-state vacuum parton shower followed by a medium-induced shower originating from elastic and radiative collisions with the medium constituents. Coherency is achieved by starting with trial gluons that act as field dressing of the initial jet parton. These are formed according to a Gunion-Bertsch seed. The QCD version of the LPM effect is attained by increasing the phase of the trial gluons through elastic scatterings with the medium. Above a phase threshold, the trial gluons will be realised and can produce coherent radiation themselves. The model has been implemented in a Monte Carlo code and has been validated by successfully reproducing the BDMPS-Z prediction for the energy spectrum. The realistic case with minimal assumptions are also produced and shown. In particular, we show the influence of various parameters on the energy spectrum and transverse momentum distribution, such as the in-medium quark masses, the energy transfer in the recoil process, and the phase accumulation criteria, especially for low and intermediate energy gluons. Future studies will allow for the interface with full simulations of the quark-gluon-plasma with hydrodynamic evolution, such as vHLLE, along with subsequent hadronisation of the jet partons in order to produce realistic distributions that can be directly compared to LHC and RHIC data.Comment: Proceedings for Hard Probes 2023 (Aschaffenburg, Germany, 26-31 March 2023). 6 pages, 8 figure

A Quantum Theory of Temporally Mismatched Homodyne Measurements with Applications to Optical Frequency Comb Metrology

The fields of precision timekeeping and spectroscopy increasingly rely on optical frequency comb interferometry. However, comb-based measurements are not described by existing quantum theory because they exhibit both large mode mismatch and finite strength local oscillators. To establish this quantum theory, we derive measurement operators for homodyne with arbitrary mode overlap. These operators are a combination of quadrature and intensity-like measurements, which inform a filter that maximizes the quadrature measurement signal-to-noise ratio. Furthermore, these operators establish a foundation to extend frequency-comb interferometry to a wide range of scenarios, including metrology with nonclassical states of light.Comment: 5 pages plus appendice

Single-cycle all-fiber frequency comb

Single-cycle pulses with deterministic carrier-envelope phase enable the study and control of light-matter interactions at the sub-cycle timescale, as well as the efficient generation of low-noise multi-octave frequency combs. However, current single-cycle light sources are difficult to implement and operate, hindering their application and accessibility in a wider range of research. In this paper, we present a single-cycle 100 MHz frequency comb in a compact, turn-key, and reliable all-silica-fiber format. This is achieved by amplifying 2 $\mu$m seed pulses in heavily-doped Tm:fiber, followed by cascaded self-compression to yield 6.8 fs pulses with 215 kW peak power and 374 mW average power. The corresponding spectrum covers more than two octaves, from below 700 nm up to 3500 nm. Driven by this single-cycle pump, supercontinuum with 180 mW of integrated power and a smooth spectral amplitude between 2100 and 2700 nm is generated directly in silica fibers. To broaden applications,few-cycle pulses extending from 6 $\mu$m to beyond 22 $\mu$m with long-term stable carrier-envelope phase are created using intra-pulse difference frequency, and electro-optic sampling yields comb-tooth-resolved spectra. Our work demonstrates the first all-fiber configuration that generates single-cycle pulses, and provides a practical source to study nonlinear optics on the same timescale.Comment: Revised versio