A simple laser linac

When a laser is focused by a lens or mirror array the field acquires a longitudinal component. Under certain conditions this longitudinal laser field could be used to accelerate an injected particle to high energies.     

An integrated optical sensor for measuring glucose concentration

We used an optical sensor combined with a Mach-Zehnder interferometric waveguide and optical fibers to measure slight changes of aqueous sugar concentrations. The merits of this sensor are simplicity, reliability, high sensitivity and continuous monitoring. The technique is based on the fact that the refractive index of sugar solution changes with the concentration of sugar. In the experiment, one arm of the interferometer is clad with glue and is thus isolated from the sugar solution. The other one is exposed to the sugar solution. A single mode fiber is directly glued onto the interferometric waveguide, to guide the light into the interferometer. If the concentration of sugar covering the waveguide changes, the phase of propagating light in the exposed arm will be changed, while the phase in the other arm is fixed. Hence the output intensity from the interferometer is directly related to the concentration of the sugar solution. The result of this experiment yields the relation between the sugar concentration and output signal. From 0% to 1% concentration of sugar solution, there is only a 1.4×10^–3 refractive index difference. Two sets of experimental data have been obtained, showing a linear relation between the sugar concentration and the output signal from our sensor. This sensor could be used for continuous monitoring of blood sugar in the human body.     

Dynamics of the pulsed free-electron laser

Calculations of coherent picosecond pulse propagation in the free-electron laser are presented, based on a theory directly coupling the Maxwell and single-particle equations. Good agreement is obtained with data of the Stanford experiment, such as the power-tuning curve and the electron energy distribution.     

Generalized gain-spread expressions for the free electron laser

Starting from a many electron hamiltonian model we derive general expressions for the unsaturated gain and spread of a free electron laser that are valid for arbitrary magnetic field configurations. The general validity of a well known gain-spread relation is demonstrated.     

Lasing without inversion III: microwave coupling induced atomic coherence

We consider the nondegenerateA quantum beat laser, and investigate the possibility of lasing without population inversion when coherence is established, between the lower levels, by applying a strong microwave field. For a specific example we calculate how much coherence may be established between the lower levels using microwave coupling. Analytical calculations are presented for both the open and closed three level atomic systems, using perturbation theory up to third order in the optical fields. Taking the linear equations, we show numerically how gain may be achieved.     

Photophysics of a sulfonated 2-hydroxyphenylbenzotriazole UV absorber in solution and in polymer substrates

The total absorption spectrum of the UV absorber sodium 2-(2′-hydroxy-5′-methylphenyl) benzotriazole sulfonate (TINS) has been resolved into contributions by two ground-state forms in acetonitrile-water solvent mixtures and hydrogen bonding polymer and protein substrates. These two ground-state species can be assigned to (i) a planar intramolecularly hydrogen bonded form which can undergo the efficient nonradiative energy dissipation process of excited-state intramolecular proton transfer (ESIPT), and (ii) a fluorescent nonplanar species in which ESIPT is effectively prevented. The mole fractions of each contributing conformer in the polymeric substrates have been estimated. In all the polymer systems studied, a significant proportion of the TINS molecules exist in the nonplanar form and thus may not contribute to photostabilization of the substrate. The proportion of nonplanar molecules varied from 11 to 86% in synthetic polymers and 20 to 41% in protein substrates.