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The natural history of the residual aorta after repair of acute type A aortic dissection is incompletely understood.During a 22-year period, 201 patients underwent repair of acute type A dissection by 25 surgeons. For 168 operative survivors, mean late follow-up for reoperation or death was 6.5 +/- 5.5 years and was 100% complete. Late blood pressure and medication history were available for 136 patients. Overall, 412 computed tomography scans were analyzed for segmental diameter and false lumen patency from 69 patients who underwent multiple follow-up imaging studies at our institution.Freedom from reoperation at 10 years (range, 1 to 170 months) was 74% +/- 5% (28 reoperations in 26 patients). A nonresected primary tear (p = 0.05), Marfan syndrome (p0. 001), elevated systolic blood pressure at follow-up (p = 0.008), and absence of beta-blocker therapy (p = 0.02) were independent predictors of late reoperation. Aortic growth between consecutive imaging studies was detected in 18% of intervals (62/343) affecting 49% patients (34/69), with mean yearly growth rate of 5.3 +/- 4.5 mm. Onset of enlargement was unpredictable and occurred 59 +/- 45 months postoperatively (range, 1 to 167 months). Risk factors for growth included aortic diameter (p0. 001), elevated systolic blood pressure (p = 0.04), and presence of a patent false lumen (p = 0.05). Maximum aortic diameter of less than 35 mm predicted growth in 11% of intervals, 35 to 49 mm in 22%, and more than 49 mm in 37% (p0.001). Different proximal or distal surgical strategies did not affect aortic growth or need for reoperation (p0.17).Optimal long-term outcome of patients with acute type A dissection demands rigorous antihypertensive therapy and lifelong radiographic follow-up because aortic enlargement can begin more than a decade postoperatively.

We outline the theory of a practical Bragg scattering technique for studying the long-range spatial order of atoms localized in one-dimensional optical lattices and we demonstrate the technique using and F = 1 → 1 transitions with lin ⊤ lin laser cooling fields. The latter transition gives a dark optical lattice. We show that the scattering by a spin grating, which may also be present, can be completely or partially filtered out by varying the polarizations of the cooling fields while holding the polarization of the probe and the detector analyser fixed. This allows the fraction of atoms that are localized to be measured. The probe field is treated as a pulse and so the technique also allows time-resolved details of the spatial structure to be studied.

The semiclassical light force on a free atom is derived as the reaction on the atom of momentum loss from and exchange between plane wave modes of a classical light field. This approach leads directly to an expression for the force that is computationally convenient for multidimensional laser field configurations under conditions where a two-level model of the atoms is appropriate, and provides insight into the origin of the light force in terms of loss, gain and exchange of mode momenta.

Theoretical results are presented for high-gain high-conversion amplification of picosecond laser pulses in a Raman medium. The influence of phase-pulling in the case of noisy pulses is investigated for both collinear and non-collinear propagation. An equivalent “average” set of equations is given which can be used to calculate the average gain characteristics of the amplifier for non-collinear noisy pulses.

A unique high-power laser system is described that is based on stimulated Raman scattering in methane. KrF-laser pump beams of 10-ps duration are confined in a square-section light guide and amplify a 268-nm Stokes-shifted beam to 0.5 TW with extremely low prepulse. The near-diffraction-limited beam quality gives a peak brightness of >1020 W cm−2 sr−1.

A large aperture KrF laser (SPRITE) based on a 27 cm diameter electron beam pumped amplifier has been developed at the Rutherford Appleton Laboratory and is in operation as a user facility. Recent development of this system has concentrated on the demands of short pulse and high brightness and this has led to two parallel program. One concentrates on efficient multiplexed energy extraction in one or more very low divergence beams using the approach known as 'Raman beam combining'. The second is directed to maximizing the brightness of a single amplified pulse by minimizing the pulse duration and using the technique of chirped pulse amplification (CPA) and recompression.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Amplification of short optical pulses in a KrF amplifier is studied theoretically with the use of a coherent interaction model that describes the dissociation on the lower electronic state rigorously in terms of the dephasing of the lower-state vibrational wave functions. The model is extended to include more than one upper vibrational level. The results are compared with those obtained from a discrete-level coherent model and from an incoherent (rate equation) approach.