An adaptive mid-infrared ultrashort pulse source for applications in coherent control

An adaptive mid-infrared (MIR) ultrashort pulse source is investigated for application to the coherent control of molecules. The MIR regime will allow access to vibrational modes of common organic bonds, and ultrashort pulse durations should enable the required interaction to occur before the energy is redistributed throughout the molecule. By using the molecular system as part of an adaptive learning loop, one can deliver the desired MIR pulse without the need for prior lengthy calculations to solve the Hamiltonian. The adaptive MIR pulse shaper is presented as a feasibility study in this thesis. It involves shaping a near-infrared (NIR) pulse using a spatial light modulator in a phase-only pulse shaper. The shaped NIR pulse is then transferred to the MIR via a synchronously pumped optical parametric oscillator (SPOPO), which is consequently measured using a nonlinear detector whose signal is used as the feedback parameter to be optimised. Using a global optimisation algorithm, initial experiments demonstrated adaptive MIR pulse shaping, achieving pulse compression and double pulse generation. The transfer of the pulse shape from the NIR to the MIR in the SPOPO however, is non-trivial and is discussed in detail, both numerically and experimentally, in this thesis. The results show that parameters such as the signal pulse bandwidth, temporal walk-off of the interacting pulses, signal gain, pump depletion, and group velocity dispersion should be considered when high fidelity transfer is required. It is also shown that, for an SPOPO based on periodically poled LiNbO3 high-fidelity transfer is possible for wavelengths centred around 3.5µm with a tunability of ±0.5µm. The investigation then progresses to the femtosecond regime where the demonstration of coherent control experiments becomes more accessible. Using a fibre-based chirped pulse amplification system, which is an attractive pump source for the SPOPO, adaptive pulse shaping is demonstrated, showing significant improvement in the quality of the 500 fs source at high pulse energies of 65µJ, as a result of the learning loop. Thus the individual components to make the adaptive MIR ultrashort pulse shaping system have all been demonstrated; namely the adaptive shaping of MIR pulses via an SPOPO, the high-fidelity transfer of NIR pump pulses to the MIR in an SPOPO, and the femtosecond NIR pump source

Green-pumped, picosecond MgO:PPLN optical parametric oscillator

We investigate the performance of a magnesium-oxide-doped periodically poled lithium niobate crystal (MgO:PPLN) in an optical parametric oscillator (OPO) synchronously-pumped by 530nm, 20ps, 230MHz pulses with an average power of up to 2W from a frequency-doubled, gain-switched laser diode seed and a multi-stage Yb:fiber amplifier system. The OPO produces ~165mW (signal, 845nm) and ~107mW (idler, 1421nm) of average power for ~1W of pump power and can be tuned from ~800nm to 900nm (signal) and 1.28µm to 1.54µm (idler). Observations of photo-refraction and green-induced infrared absorption (GRIIRA) in different operational regimes of the MgO:PPLN OPO are described and the role of peak intensity and average power are investigated, both with the aim to find the optimal operating regime for pulsed systems

Analytical modelling of Tm-doped tellurite glass including cross-relaxation process

In this paper, we present a comprehensive analytical model of Tm able to take into account direct cross-relaxation process. We show that by using an appropriate set of parameters the model is able to properly fit the first part of the fluorescence decay of Tm-doped tellurite glasses for different dopant concentration values. We also compare the model with a full numerical model to investigate its limitations. We assess the model is a valid tool to fit fluorescence properties but for precisely predicting population inversion is limited to doping level up to about 1%. In fact, we show the reverse cross-relaxation process becomes significant in case of higher doping level

Seasonal Propagation Characteristics of MSTIDs Observed at High Latitudes Over Central Alaska Using the Poker Flat Incoherent Scatter Radar

Near‐continuous electron density measurements obtained over a ∼3 year period, 2010–2013, using the Poker Flat Incoherent Scatter Radar (PFISR) in central Alaska (69°N, 147°W) have been analyzed to quantify the properties of over 650 high‐latitude medium‐scale traveling ionospheric disturbances (MSTIDs). Our analysis focused on the altitude range 100–300 km encompassing the lower ionosphere/thermosphere and yielded first full seasonal day/night distributions of MSTIDs at high northern latitudes with mean values: horizontal wavelength 446 km, horizontal phase speed 187 m/s, and period 41 min. These year‐round measurements fill an important summertime gap in existing MSTID measurements revealing predominantly eastward wave propagation during the summer, while continued winter season observations agree well with previous reports of near southward propagating MSTIDs. Our 3 years of results suggest a cyclic change in the seasonal horizontal propagation directions that was found to be quantitatively consistent with critical level wind and dissipative filtering. Concurrent measurements of the vertical wavelength spectrum as a function of altitude also compared favorably in shape with that calculated using a theoretical dispersion relation (Vadas & Fritts, 2005, https://doi.org/10.1029/2004JD005574) for the thermosphere, but with a higher mean value. Evidence supporting the systematic broadening and shrinking in the azimuthal distributions of the MSTIDs during the course of the year was also found, as well as an unexpected correlation between the MSTID propagation directions and the AE index, both of which are under further investigation

Accommodation functions: co-dependency and relationship to refractive error

We assessed the extent to which different accommodative functions are correlated and whether accommodative functions predict the refractive error or the progression of myopia over a 12 month period in 64 young adults (30 myopes and 34 non-myopes). The functions were: amplitude of accommodation; monocular and binocular accommodative facility (6 m and 40 cm); monocular and binocular accommodative response to target distance; AC/A and CA/C ratios, tonic accommodation (dark focus and pinhole), accommodative hysteresis, and nearwork-induced transient myopia. Within groups of related accommodative functions (such as facility measures or open-loop measures) measurements on individuals were generally significantly correlated, however correlations between functions from different groups were generally not significant. Although accommodative amplitude and pinhole (open loop) accommodation were significantly different in myopes than in non-myopes, these functions were unrelated to myopia progression. Facility of accommodation and accommodative lag was independent predictors of myopia progression

Going it alone won’t work! The relational imperative for social innovation in social enterprises

Shifts in the philosophy of the “state” and a growing emphasis on the “Big Society” have placed an increasing onus on a newly emerging organizational form, social enterprises, to deliver innovative solutions to ease societal issues. However, the question of how social enterprises manage the process of social innovation remains largely unexplored. Based on insights from both in-depth interviews and a quantitative empirical study of social enterprises, this research examines the role of stakeholder relationships in supporting the process of social innovation within social enterprises. We find that social enterprises are adept at working with their stakeholders in the ideation stage of social innovation. In contrast, they often fail to harness knowledge and expertise from their partners during the social innovation implementation phase. Consequently, we propose a social innovation–stakeholder relationship matrix that provides social enterprises in particular with insight for developing stakeholder relationships to achieve their social innovation missions

Retrospective evaluation of whole exome and genome mutation calls in 746 cancer samples

Funder: NCI U24CA211006Abstract: The Cancer Genome Atlas (TCGA) and International Cancer Genome Consortium (ICGC) curated consensus somatic mutation calls using whole exome sequencing (WES) and whole genome sequencing (WGS), respectively. Here, as part of the ICGC/TCGA Pan-Cancer Analysis of Whole Genomes (PCAWG) Consortium, which aggregated whole genome sequencing data from 2,658 cancers across 38 tumour types, we compare WES and WGS side-by-side from 746 TCGA samples, finding that ~80% of mutations overlap in covered exonic regions. We estimate that low variant allele fraction (VAF < 15%) and clonal heterogeneity contribute up to 68% of private WGS mutations and 71% of private WES mutations. We observe that ~30% of private WGS mutations trace to mutations identified by a single variant caller in WES consensus efforts. WGS captures both ~50% more variation in exonic regions and un-observed mutations in loci with variable GC-content. Together, our analysis highlights technological divergences between two reproducible somatic variant detection efforts

Theoretical and numerical investigations of parametric transfer via difference frequency generation for indirect mid-infrared pulse shaping

We theoretically and numerically investigate indirect mid-infrared pulse shaping via parametric transfer, specifically difference-frequency generation. We define a quantitative measure for the fidelity of parametric transfer, and investigate the effect of material dispersion and process nonlinearity on the parametric transfer. We show that a good fidelity transfer of a broad-bandwidth pulse can be efficiently achieved with a reasonable wavelength tunability, by careful design of the experimental configuration