Passive mode-locking of flashlamp pumped Rhodamine dye-lasers

A simple dye-laser system is described in which Rhodamine dyes are pumped by a co-axial linear air flashlamp in a cylindrical elliptical pumping reflector. Output pulses lasting up to 1.5sec and containing up to 250 mJ energy, have been successfully mode-locked to produce 100% modulated pulse trains. Employing a diffraction grating as cavity reflector to tune the laser frequency, in each case, for maximum absorption by the same Q-switching dye, successful mode-locking has been achieved with both Rhodamine B and Rhodamine 6G. Time resolved emission spectra have been recorded with an image tube streak camera and the effect of resonant reflectors has been studied.This work was described in a paper presented at the IEEE Conference on Laser Engineering and Applications, Washington, May 1969.     

Organo-imido alkoxides of tungsten(VI). The crystal and molecular structures of [W(NPh)(μ-OMe)(OMe)3]2 and [W(NPh)(OCMe3)3Cl(NH2CMe3)]

Reaction of phenylimido tungsten tetrachloride with MeOH and t-butylamine gave the dimeric complexes [W(NPh)(μ-OMe)(OMe)₃]₂ and [W(NPh)(μ-OMe)(OMe)₂Cl]₂. With ethanol [W(NPh)(μ-OEt)(OEt)₂Cl]₂ was formed whereas isopropyl and neopentyl alcohols gave the monomeric complexes [W(NPh)(OR)₄(NH₂CMe₃)](R = CHMe₂, CH₂CMe₃); t-butanol gave [W(NPh)(OCMe₃)3Cl(NH₂CMe₃)] which could not be converted to [W(NPh) (OCMe₃)₄]. Further reaction of [W(NPh)(μ-OMe)(OMe)₃]₂ with o-HOC₆H₄CH = NC₆H₃Me₂(salim-H) gave the salicylaldimine complex [W(NPh)(OMC)₃(salim)]. The products were characterised by analytical data, IR, ¹H NMR, ¹³C NMR and mass spectroscopy. The crystal and molecular structures of the title complexes have been determined from single crystal X-ray diffractometer data. Crystals of [W(NPh)(μ-OMe)(OMe)₃]₂are triclinic with a = 8.473(7), b = 10.776(5), c = 7.683(Å, α = 102.26(3), β = 102.68(4), γ = 71.13(6)°, space group P$\text{1}$ Crystals of 3) [W(NPh)(OCMe₃)₃Cl(NH₂CMe₃) are monoclinic with a = 9.341(2), b = 29.608(7), c = 10.257(2) Å, β = 106.28(2)°, space group, P2₁/c. Both structures were solved by Patterson and Fourier methods and refined to R = 0.075 for the 1022 observed data of [W(NPh) (μ-OMe)(OMe)₃]₂ and to R = 0.074. For the 2033 observed data of [W(NPh)(OCMe₃)₃Cl(NH₂CMe₃). The former molecule is shown to be a dimer, the two halves of the molecule being related by a centre of symmetry. Both W atoms adopt a distorted octahedral coordination geometry and they are linked by two methoxy bridges. Trans to one of the bridging donors is the phenyl imido group with a WN bond length of 1.61(4) Å; the remaining coordination sites are filled with methoxy groups. The structure of W(NPh)(OCMe₃)₃ Cl(NH₂CMe₃) is monomeric with the phenylimido group trans to the NH₂CMe₃ ligand in a distorted octahedral coordination geometry. Remaining sites are filled with the chloride and 3 OCMe₃ ligands. The WN (imido) bond length is 1.71(2) Å, whilst WN(amine) is 2.40(2) Å     

Aluminium triflate: a remarkable Lewis acid catalyst for the ring opening of epoxides by alcohols

Al(OTf)3 was found to be an extremely effective catalyst (at ppm levels) for ring opening reactions of epoxides using a range of alcohols.     

Strong coupling in a microcavity LED

Thin films of polyelectrolyte/J aggregate dye bilayers with high absorption coefficient (6 nm thick with alpha approximately equal to 1.0 x 10(6) cm(-1)) inserted in an optical microcavity enable the cavity quantum electrodynamic strong coupling limit to be reached at room temperature with a coupling strength (Rabi splitting) of 265 +/- 15 meV. By embedding these films in a resonant cavity organic LED structure, we demonstrate the first emissive electrically pumped exciton-polariton device.     

On the relationship between signal bandwidth and frequency correlation for ocean surface forward scattered signals

The relationship between the bandwidth of a signal and the correlation of that signal with its ocean surface reflected arrival, a quantity we term frequency correlation, has been investigated experimentally and compared with two theories. Decorrelation of wideband surface scattered signals is a direct consequence of time spread. The acoustic measurement utilized a very short pure tone signal, from which time spread has been estimated, and four broadband signals with different bandwidths, for which correlation with the transmitted signal has been measured. An environment-driven model developed by Dahl was used to predict time spread, which agreed favorably with our time spread measurements. The model was also employed in two theories that predict frequency correlation. The first, a theory published by Reeves in 1974, is based upon the ratio of signal temporal resolution to total time spread. This theory compared well with our measurements for 1 kHz bandwidth signals, but is not applicable for signal bandwidths greater than about 2 kHz. The second, a theory developed by Ziomek, models ocean acoustic propagation as transmission through a linear system. This theory agreed well with our frequency correlation measurements for signal bandwidths of 1-22 kHz.     

Ultrafast all-optical modulation on a silicon chip

We experimentally demonstrate ultrafast all-optical modulation using a micrometer-sized silicon photonic integrated device. The device transmission is strongly modulated by photoexcited carriers generated by low-energy pump pulses. A p-i-n junction is integrated on the structure to permit control of the generated carrier lifetimes. When the junction is reverse biased, carriers are extracted from the device in a time as short as 50 ps, permitting greater than 5 Gbit/s modulation of optical signals on a silicon chip.     

Polyborane reactions in ionic liquids: new efficient routes to functionalized decaborane and o-carborane clusters

In contrast to reactions that have been observed in traditional organic solvents, decaborane olefin-hydroboration and alkyne-insertion reactions have been found to proceed in ionic liquid solvents without the need of a catalyst. These reactions now provide important new, high-yield synthetic pathways to functionalized decaborane and o-carborane clusters.     

Charge transfer from ammonia physisorbed on nanotubes

We report the use of nanotube field-effect transistor devices for chemical sensing in a conducting liquid environment. Detection of ammonia occurs through the shift of the gate voltage dependence of the source-drain current. We attribute this shift to charge transfer from adsorbed ammonia molecules, with the amount of charge estimated to be as small as 40 electrons for the smallest shift detected. Using the concentration dependence of the response as an adsorption isotherm, we are able to measure the amount of charge transfer to be 0.04 electron per ammonia molecule.     

Dyad beads and the combinatorial discovery of catalysts

Dyad beads, bearing both a substrate and a catalyst, were prepared to enable direct split and mix bead based screening for catalysis.