Direct spatial-temporal discrimination of modes in a photonic lightwave circuit using photon scanning tunnelling microscopy

Multi-mode photonic lightwave circuits (PLCs) provide new avenues for extending the performance of single mode systems. As an example, they can potentially provide increased bandwidth by multiplexing information into different waveguide modes[1]. For practical applications of multi-mode PLCs to be developed, a measurement technique is required to investigate detailed mode profiles and propagation constants in complex circuits. Photon scanning tunnelling microscopy (PSTM) provides a means of experimentally tracking the femtosecond inter-modal delays observed in PLCs with the ability to discriminate modes by their spatial profiles inside the waveguide

Nonlinear ptychographic coherent diffractive imaging

Ptychographic Coherent diffractive imaging (PCDI) is a significant advance in imaging allowing the measurement of the full electric field at a sample without use of any imaging optics. So far it has been confined solely to imaging of linear optical responses. In this paper we show that because of the coherence-preserving nature of nonlinear optical interactions, PCDI can be generalised to nonlinear optical imaging. We demonstrate second harmonic generation PCDI, directly revealing phase information about the nonlinear coefficients, and showing the general applicability of PCDI to nonlinear interactions

High intensity pulse self-compression in short hollow core capillaries

The drive for shorter pulses for use in techniques such as high harmonic generation and laser wakefield acceleration requires continual improvement in post-laser pulse compression techniques. The two most commonly used methods of pulse compression for high intensity pulses are hollow capillary compression via self-phase modulation (SPM) [1] and the more recently developed filamentation [2]. Both of these methods can require propagation distances of 1-3 m to achieve spectral broadening and compression. Additionally, hollow capillary compression requires post compression of the broadened pulse by chirped mirrors. Filamentation trades the efficiency of hollow capillary compression (67%) for ionisation-induced pulse self-compression. A mixture of SPM and plasma generation increases the spectral bandwidth of the pulse; however this occurs only in a small region at the centre of the beam. Spatial filtering is required to achieve the shortest pulses, reducing the efficiency to 20%. Although the majority of hollow core capillary compression requires long propagation distances, compression in short capillaries [3] with significant plasma generation has been demonstrated to be a promising technique

A practical microwave method for the synthesis of fluoromethy 4-methylbenzenesulfonate in tert-amyl alcohol

YesFluorine substitution is an established tool in medicinal chemistry to favourably alter the molecular properties of a lead compound of interest. However, gaps still exist in the library of synthetic methods for accessing certain fluorine-substituted motifs. One such area is the fluoromethyl group, particularly when required in a fluoroalkylating capacity. The cold fluorination of methylene ditosylate is under evaluated in the literature, often proceeding with low yields or harsh conditions. This report describes a novel microwave method for the rapid nucleophilic fluorination of methylene ditosylate using inexpensive reagents in good isolated yield (65%)

Defect production in silica fibers doped with Tm³⁺

Irradiation of Tm3+ fibers with blue light at 476 nm induces a broad-bandwidth loss in these fibers. We have measured the spectral dependence of the loss for both silica-germania and silica-alumina fibers and show through micro-Raman studies of the core regions of the fibers that this induced loss is correlated with the production of structural defects in the glass host

Diode-pumped, ion-exchanged Er/Yb waveguide laser at 1.5µm in phosphorus-free silicate glass

We demonstrate the first diode-pumped, planar ErNb waveguide laser. The device was fabricated by thallium-exchange in a phosphorus-free silicate glass. Lasing was achieved with a low threshold of 15 mW, indicating the absence of the severe backtransfer effects previously reported in Er/Yb bulk laser silicate glasses

High-energy laser-pulse self-compression in short gas-filled fibers

We examine the spatiotemporal compression of energetic femtosecond laser pulses within short gas-filled fibers. The study is undertaken using an advanced nonlinear pulse propagation model based on a multimode generalized nonlinear Schrödinger equation that has been modified to include plasma effects. Plasma defocusing and linear propagation effects are shown to be the dominant processes within a highly dynamical mechanism that enables 100-fs pulses to be compressed into the few-cycle regime after <50 mm of propagation. Once the mechanism has been introduced, parameter spaces are explored and compressor designs suitable for performing high-field experiments in situ are presented. We finish by showing how these designs may be extended to novel wavelengths and driving pulses delivered by state-of-the-art high-repetition-rate lasers

Soft systems methodology: a context within a 50-year retrospective of OR/MS

Soft systems methodology (SSM) has been used in the practice of operations research and management science OR/MS) since the early 1970s. In the 1990s, it emerged as a viable academic discipline. Unfortunately, its proponents consider SSM and traditional systems thinking to be mutually exclusive. Despite the differences claimed by SSM proponents between the two, they have been complementary. An extensive sampling of the OR/MS literature over its entire lifetime demonstrates the richness with which the non-SSM literature has been addressing the very same issues as does SSM

An alternative synthesis of Vandetanib (CaprelsaTM) via a microwave accelerated Dimroth rearrangement

YesVandetanib is an orally available tyrosine kinase inhibitor used in the treatment of cancer. The current synthesis proceeds via an unstable 4-chloroquinazoline, using harsh reagents, in addition to requiring sequential protection and deprotection steps. In the present work, use of the Dimroth rearrangement in the key quinazoline forming step enabled the synthesis of Vandetanib in nine steps (compared to the previously reported 12–14).This work was supported by the Cancer Research UK-Cancer Imaging Centre (grant: C1060/ A16464), the Institute of Cancer Research and the University of Hull