ABSTRACT
We experimentally demonstrate an integrated semiconductor source of counterpropagating twin photons in the telecom range. A pump beam impinging on top of an AlGaAs waveguide generates parametrically two counterpropagating, orthogonally polarized signal/idler guided modes. A 2 mm long waveguide emits at room temperature one average photon pair per pump pulse, with a spectral linewidth of 0.15 nm. The twin character of the emitted photons is ascertained through a time-correlation measurement. This work opens a route towards new guided-wave semiconductor quantum devices.
ABSTRACT
We measure the efficiency of converting high-power 15-fs 0.8-mum pulses to the mid infrared in GaAs and GaSe as well as the pulse duration and the spectrum of the infrared radiation that is produced. Free-carrier production limits the conversion efficiency in GaAs to approximately 5x10(-7) , allowing us to produce 2.5-pJ, 30-fs pulses spanning the spectral range from 6 to 14 mum . In GaSe we obtain, in a moderately saturated regime, a conversion efficiency of 7.5x10(-5) , limited by two-photon absorption, allowing us to produce pulses of 100-fs duration containing 10 nJ of energy.
ABSTRACT
We demonstrate broadband infrared pulse shaping by difference-frequency mixing of two visible phase-locked linearly chirped pulses in GaAs. Control of the temporal profile of the emitted field is achieved through this direct tailoring of the exciting visible intensity. The results are in agreement with a simulation with no adjustable parameter.
ABSTRACT
The interference between different harmonics of a few-cycle optical pulse in the region of the spectral overlap is sensitive to the phase of the optical carrier inside the pulse envelope. Near-surface third-harmonic generation from Si(001) combined with second-harmonic generation in a 10-mum -thick beta-barium borate crystal produces sufficiently strong harmonic emission for single-shot measurement. We propose using this technique to measure the carrier envelope phase of high-energy 5-fs pulses.
ABSTRACT
Using Fourier-transform spectral interferometry, we demonstrate the measurement of both amplitude and phase of photon echoes in GaAs multiple-quantum-well structures. The complete measurement of the electric field thus achieved makes possible the determination of the corresponding Wigner spectrograms.
ABSTRACT
We present time-resolved pump-probe experiments on a semiconductor in which the signal shape, dominated by perturbed free polarization decay, is strongly dependent on the probe pulse's spectral shape. This effect can be used efficiently to reduce large spectral oscillations that prevent the observation of weak signals near a narrow spectral structure.
ABSTRACT
Bovine Cu Zn SOD was used during an 8 year period as an antiinflammatory drug in 26 patients with severe Crohn's disease (CDAI 300) usually after failure of corticotherapy or when this drug was discontinued because of side effects or infection. This was a phase II trial during which doses routes of administration and concomitant therapies were progressively modified. We obtained 73% good short term responses (judged upon CDAI and anatomic healing) and 82% positive results on long term evolution (the criteria were: i CDAI lower than 100 in between relapses, ii complete healing or notable improvement of lesions, iii no surgery needed, iv return to work. The acceptability was excellent with the free enzyme. Since the above described experience, published in Free Radical Biology and Medicine (1989, 7: 145-151), we used always the same treatment schedule (SOD 8 mg/day associated with Desferroxamine--500 mg subcutaneous every 2 days). The follow-up during the 87-89 period showed that 12 are in good health without any relapse, 9 experienced one or more relapses, and showed good responses upon resumption of treatment, 5 failed to respond to treatment, all part of the initial group on which SOD treatment had already failed, and among whom 3 were lost for follow-up before 1987, and two others took up another SOD treatment which also failed. 3 new patients (2 females, 1 male) were treated since then, and all 3 had positive results (one with disappearance of ileocoecal mass). The efficacy of SOD as an antiinflammatory drug in Crohn's disease needs to be confirmed by controlled trials.
Subject(s)
Anti-Inflammatory Agents, Non-Steroidal , Crohn Disease/drug therapy , Superoxide Dismutase/therapeutic use , Copper/chemistry , Drug Evaluation , Female , Follow-Up Studies , Humans , Male , Zinc/chemistryABSTRACT
Free oxygen radicals (F.O.R.) belong to a very aggressive chemical species derived from molecular oxygen. Their role in inflammation is well established and Polymorphonuclear neutrophils (PMNS) make use of them as antibacterial weapons. Their role has been experimentally demonstrated in numerous ischemia-reperfusion models. Free radical scavengers such as the superoxide dismutase, allopurinol or desferrioxamine can prevent the occurrence of lesions. The essential role of PMNS in these models is demonstrated by the fact that previous depletion of the animal in PMNS also prevents such lesions. Histologically, in these ischemia-reperfusion models, PMNS infiltration may be quantified by assay of myeloperoxidase. In experimental models of inflammatory colitis (acetic acid, bacterial polysaccharides) intestinal wall infiltration by PMNS is a fundamental phenomenon and is also a characteristic of Crohn's disease and exacerbations of Ulcerative Colitis. Thus, it is probable in both disorders that F.O.R. play an important role since steroids inhibit their secretion by PMNS and 5-aminosalicylic acid has been shown to be a F.O.R. scavenger.
Subject(s)
Inflammatory Bowel Diseases/etiology , Oxygen/metabolism , Reperfusion Injury/physiopathology , Free Radicals , Humans , Inflammation/physiopathology , Neutrophils/physiology , Superoxide Dismutase/metabolism , Superoxides/metabolismABSTRACT
The effectiveness of 2 hematins administered by intravenous infusion was compared in acute intermittent porphyria. Judging from subjective symptoms (abdominal pain), clinical improvement was complete and constant. There was a rapid decrease in urinary excretion of porphyrins precursors, with a clearer response of delta-aminolevulinic acid than of porphobilinogen. Urine levels of uroporphyrin often returned to normal after two infusions. The drugs were very well tolerated. Provided it is administered early, before neurological complications develop, treatment with hematin completely relieves abdominal symptoms and suppresses most of the biochemical changes associated with hepatic porphyria.