Observation of high transient gain in the germanium x-ray laser at 19.6 nm

The transient-excitation pumping scheme, in which a picosecond duration pulse rapidly heats the plasma preformed by a low-intensity nanosecond pulse, was used to pump the Ne-like germanium, J = 0-1 transition at 19.6 nm. A small-signal gain coefficient of 30 cm(-1) was measured for targets less than or equal to 5 mm long. (C) 1998 Optical Society of America.

A study to optimise the temporal drive pulse structure for efficient XUV lasing on the J=0-1, 19.6 nm line of Ge XXIII

Short pulses of 100 ps FWHM duration at 1.06 mu m wavelength are used as the pump source for driving the J = 0-1, 19.6 nm, Ne-like germanium X-ray laser. Different combinations of short pulses are investigated and quantitatively compared. Configurations investigated include a single pulse, double pulses at 400 ps and 800 ps separation, single pulses with prepulses and double pulses with prepulses. Data are presented in the form of integrated energy measurements, and supported by modelling. The most efficient short pulse configurations are shown to be orders of magnitude more effective than pumping with nanosecond duration pulses. (C) 1997 Elsevier Science B.V.

Saturated output of a Ge XXIII x-ray laser at 19.6 nm

We report on measurements of the saturated single frequency output of a Ge XXIII x-ray laser on the J=0-->1 transition at 19.6 nm from a refraction compensating double target driven by 150 J of energy from 75-ps Nd-glass laser pulses. The 19.6-nm line completely dominated the laser output. The output energy was measured to be 0.9 mJ in a beam of 6.6x30 mrad(2) divergence, corresponding to a conversion efficiency of 6 x 10(-6).

Using low and high prepulses to enhance the J=0-1 transition at 19.6 nm in the Ne-like germanium XUV laser

We report a study of the effect of prepulses on XUV lasing of Ne-like germanium for an irradiation geometry where approximate to 20 mm long germanium slab targets were irradiated at approximate to 1.6 x 10(13) W cm(-2) using approximate to 0.7 ns (1.06 mu m) pulses from the VULCAN glass laser. Prepulses were generated at fractional power levels of approximate to 2 x 10(-4) (low) and approximate to 2 x 10(-2) (high) and arrived on target 5 and 3.2 ns respectively in advance of the main heating pulse, For both the low and high prepulses the output of the 3p-3s, J = 0-1, line at 19.6 nm was enhanced such that the peak radiant density (J/st) for this line became greater than that for the normally stronger J = 2-1 lines at 23.2 and 23.6 nm. The J = 0-1 line, whose FWHM duration was reduced from approximate to 450 ps to approximate to 100 ps, delivered approximate to 6 x more power (W) than the average for the combined J = 2-1 lines, whose FWHM duration was approximate to 500 ps for both levels of prepulse, The higher prepulse was more effective, yielding approximate to 2 x more radiant density and approximate to 7 x more power on both the J = 0-1 and J = 2-1 transitions compared to the low prepulse case, The most dramatic observation overall was the approximate to 40 x increase of power in the J = 0-1 line for the high prepulse (approximate to 2%) case compared with the zero prepulse case. These observations, coupled with measurements of beam divergence and beam deviation through refractive bending, as well as general agreement with modelling, lead us to conclude that, for germanium, the main influence of the prepulse is (a) to increase the energy absorbed from the main pulse, (b) to increase the volume of the gain zone and (c) to relax the plasma density gradients, particularly in the J = 0-1 gain zone.

High contrast plasma mirror: spatial filtering and second harmonic generation at 10(19)Wcm(-2)

Recently, the use of plasma optics to improve temporal pulse contrast has had a remarkable impact on the field of high- power laser-solid density interaction physics. Opening an avenue to previously unachievable plasma density gradients in the high intensity focus, this advance has enabled researchers to investigate new regimes of harmonic generation and ion acceleration. Until now, however, plasma optics for fundamental laser reflection have been used in the sub-relativistic intensity regime (10(15) - 10(16)Wcm(-2)) showing high reflectivity (similar to 70%) and good focusability. Therefore, the question remains as to whether plasma optics can be used for such applications in the relativistic intensity regime (> 10(18)Wcm(-2)). Previous studies of plasma mirrors (PMs) indicate that, for 40 fs laser pulses, the reflectivity fluctuates by an order of magnitude and that focusability of the beam is lost as the intensity is increased above 5 x 10(16)Wcm(-2). However, these experiments were performed using laser pulses with a contrast ratio of similar to 10(7) to generate the reflecting surface. Here, we present results for PM operation using high contrast laser pulses resulting in a new regime of operation - the high contrast plasma mirror (HCPM). In this regime, pulses with contrast ratio > 10(10) are used to form the PM surface at > 10(19)Wcm(-2), displaying excellent spatial filtering, reflected near- field beam profile of the fundamental beam and reflectivities of 60 +/- 5%. Efficient second harmonic generation is also observed with exceptional beam quality suggesting that this may be a route to achieving the highest focusable harmonic intensities. Plasma optics therefore offer the opportunity to manipulate ultra-intense laser beams both spatially and temporally. They also allow for ultrafast frequency up-shifting without detrimental effects due to group velocity dispersion (GVD) or reduced focusability which frequently occur when nonlinear crystals are used for frequency conversion.

Critical assessment of two-qubit post-Markovian master equations

A post-Markovian master equation has been recently proposed as a tool to describe the evolution of a system coupled to a memory-keeping environment [A. Shabani and D. A. Lidar, Phys. Rev. A 71, 020101 ( R) ( 2005)]. For a single qubit affected by appropriately chosen environmental conditions, the corresponding dynamics is always legitimate and physical. Here we extend such a situation to the case of two qubits, only one of which experiences the environmental effects. We show how, despite the innocence of such an extension, the introduction of the second qubit should be done cum grano salis to avoid consequences such as the breaking of the positivity of the associated dynamical map. This hints at the necessity of using care when adopting phenomenologically derived models for evolutions occurring outside the Markovian framework.

Relevance of breast cancer hormone receptors and other factors to the efficacy of adjuvant tamoxifen: patient-level meta-analysis of randomised trials

Background: As trials of 5 years of tamoxifen in early breast cancer mature, the relevance of hormone receptor measurements (and other patient characteristics) to long-term outcome can be assessed increasingly reliably. We report updated meta-analyses of the trials of 5 years of adjuvant tamoxifen.
Methods: We undertook a collaborative meta-analysis of individual patient data from 20 trials (n=21457) in early breast cancer of about 5 years of tamoxifen versus no adjuvant tamoxifen, with about 80% compliance. Recurrence and death rate ratios (RRs) were from log-rank analyses by allocated treatment.
Findings: In oestrogen receptor (ER)-positive disease (n=10 645), allocation to about 5 years of tamoxifen substantially reduced recurrence rates throughout the first 10 years (RR 0.53 [SE 0.03] during years 0-4 and RR 0.68 [0.06] during years 5-9 [both 2p<0.00001]; but RR 0.97 [0.10] during years 10-14, suggesting no further gain or loss after year 10). Even in marginally ER-positive disease (10-19 fmol/mg cytosol protein) the recurrence reduction was substantial (RR 0.67 [0.08]). In ER-positive disease, the RR was approximately independent of progesterone receptor status (or level), age, nodal status, or use of chemotherapy. Breast cancer mortality was reduced by about a third throughout the first 15 years (RR 0.71 [0.05] during years 0-4, 0.66 [0.05] during years 5-9, and 0.68 [0.08] during years 10-14; p<0.0001 for extra mortality reduction during each separate time period). Overall non-breast-cancer mortality was little affected, despite small absolute increases in thromboembolic and uterine cancer mortality (both only in women older than 55 years), so all-cause mortality was substantially reduced. In ER-negative disease, tamoxifen had little or no effect on breast cancer recurrence or mortality.
Interpretation: 5 years of adjuvant tamoxifen safely reduces 15-year risks of breast cancer recurrence and death. ER status was the only recorded factor importantly predictive of the proportional reductions. Hence, the absolute risk reductions produced by tamoxifen depend on the absolute breast cancer risks (after any chemotherapy) without tamoxifen.
Funding: Cancer Research UK, British Heart Foundation, and Medical Research Council.

Randomised controlled trial of ranitidine versus omeprazole in combination with antibiotics for eradication of Helicobacter pylori

This study compared high dose ranitidine versus low dose omeprazole with antibiotics for the eradication of H pylori. 80 patients (mean age 48 years, range 18-75) who had H pylori infection were randomised in an investigator-blind manner to either a two-week regime of omeprazole 20 mg daily, amoxycillin 500 mg tid and metronidazole 400 mg tid (OAM), or ranitidine 600 mg bd, amoxycillin 500 mg tid and metronidazole 400 mg tid (RAM), or omeprazole 20 mg daily and clarithromycin 500 mg tid (OC), or omeprazole 20 mg daily and placebo (OP). H pylori was eradicated in 6 of 19 patients in the OAM group (32%); 8 of 18 in the RAM group (44%), 4 of 15 in the OC group (27%); none of 18 in the OP group (0%). [<P0.005 for OAM, RAM, OC vs OP; P = N.S. between OAM, RAM, OC]. Overall metronidazole resistance was unexpectedly high at 58%. Eradication rates in metronidazole sensitive patients were 71% (5/7) and 100% (3/3) for OAM and RAM respectively. In conclusion, H pylori eradication rates using high dose ranitidine plus amoxycillin and metronidazole may be similar to that of low dose omeprazole in combination with the same antibiotics for omeprazole with clarithromycin. Overall eradication rates were low due to a high incidence of metronidazole resistance but were higher in metronidazole-sensitive patients. Even high dose ranitidine with two antibiotics achieves a relatively low eradication rate. These metronidazole-based regimens cannot be recommended in areas with a high incidence of metronidazole resistance.