Fused silica ablation by double ultrashort laser pulses with dual wavelength and variable delays.

Today, glass and other similar dielectric materials are widely used in modern manufacturing. However, glass is a brittle and a heat sensitive material. Laser technology is used to process glass but quality and throughput are still a key issue. In the present paper, we investigate dual-wavelength double ultrashort laser pulses in order to control free electrons dynamics and subsequent ablation for fused silica processing, and further improve the understanding of this laser-material interaction. We used a high average power Yb-doped femtosecond laser source (100 W) with two optical lines exhibiting different pulse durations and wavelengths (500 fs at 515 nm; and 1 or 10 ps at 1030 nm) with various fluences and delays. The best configuration in terms of ablation efficiency is expected to take place when the green pulse first induces free electrons, followed by their heating by the red pulse. The obtained results are discussed in terms of optical transmission as well as ablated volume, and are compared with single pulse ablation. Our experimental results are supported by absorbed energy density calculations based on a model considering the two-color laser induced electron dynamics, including photoionization, laser heating of free electrons, and their recombination. We demonstrate that there is an optimal cooperating effect between the two sub-pulses for a 1-ps delay, nevertheless there is no beneficial effect in splitting the beam for optimizing fused silica ablation compared with the single-pulse green configuration.

Pulse to pulse control for highly precise and efficient micromachining with femtosecond lasers.

Micromachining with high repetition rate femtosecond lasers and galvo scanners shows some limitations in the pulses positioning accuracy due to the galvo mirrors acceleration. This is particularly evident during scan speed or direction changes, resulting in a poor quality and overtreatment e.g. in corners. Several scanning approaches have been proposed to tackle these issues like the so-called skywriting (SW) and the pulse-on-demand (POD) being the last limited to ns lasers, moderate pulse repetition rates and scan speeds. Recently, POD approach has been extended to femtosecond laser sources with high power and high repetition rate. Here, for the first time, we explored the huge potential in laser micromachining of femtosecond POD technology associated to a fast galvo scanner. We tested an innovative set-up allowing for precise laser triggering at the requested time and position for MHz repetition rate and scan speed as high as 20 m/s. The pulse position accuracy of the system has been estimated to be ≤ 1µm whilst performances have been evaluated in comparison to conventional scanning and SW. Finally, we report the results of an engraving test on stainless steel. The advantages of the approach we propose are clearly shown in terms of machining quality and precision with respect to conventional scanning and reduction of the processing time by ≈ 40% with respect to SW.

Yb:CaGdAlO4 thin-disk laser.

We present the first demonstration of a Yb:CALGO thin-disk laser. In a slightly multimode configuration, we obtained up to 30 W of average power at a slope efficiency of 40% and an optical-to-optical efficiency of 32%. With a single-mode cavity, an average power of 25 W was achieved. A tuning range from 1018 to 1052 nm could be demonstrated by inserting a prism into the cavity. In the Q-switched regime, we obtained 1 mJ of pulse energy at a repetition rate of 100 Hz.

Passively mode-locked diode-pumped Nd:YVO4 oscillator operating at an ultralow repetition rate.

We demonstrate the operation of an ultralow-repetition-rate, high-peak-power, picosecond diode-pumped Nd:YVO4 passively mode-locked laser oscillator. Repetition rates lower than 1 MHz were achieved with the use of a new design for a multiple-pass cavity and a semiconductor saturable absorber. Long-term stable operation at 1.2 MHz with a pulse duration of 16.3 ps and an average output power of 470 mW, corresponding to 24-kW peak-power pulses, is reported. These are to our knowledge the lowest-repetition-rate high-peak-power pulses ever generated directly from apicosecond laser resonator without cavity dumping.

A support group for children with one parent with cancer: report on 4 year experience of a talking group. / Le soutien des enfants ayant un parent atteint de cancer: description de 4 années de fontionnement d'un groupe de parole.

Children of a parent diagnosed with cancer, experience severe emotional distress, which may have important repercussions later, in adult life. However, responses of children to a parent with a serious illness vary, depending on the functioning of the family unit, and more especially, the capacity of the family to communicate openly and effectively about the parent's illness. A support group has now been established at IGR for children of parents undergoing treatment for cancer, in order to help foster intra-familial communication about coping with illness. The group is open to children and other family members and consists of a non-structured discussion of approximately 2 hours. The support group is animated by a psychologist and a doctor. In 4 years, 175 children, aged from 6 months to 23 years, from 98 families have participated in the programme. The emotional and behavioural conduct of the children and their family were analysed. Children were encouraged to express their fears concerning their parent's illness and age-appropriate medical information was given in response to their questions. As a result of this opportunity to express and share feelings with others, children's anxiety was shown to be considerably lessened and a renewal of discussion within the family followed in the majority of cases. Nevertheless, the dynamics of these groups can be delicately balanced. It is therefore paramount that the animation of such groups be confined to experienced professionals.

Totally implanted catheters to reduce catheter-related infections in patients receiving interleukin-2: a 2-year experience.

A high incidence of bacterial infections has been previously reported during interleukin-2 (IL-2) treatment, mainly due to catheter-related infections. Antibiotic prophylaxis has been successfully used to decrease such infections. The goal of this study was to evaluate an alternative way to reduce catheter-related infections in IL-2-treated patients by the use of totally implanted catheters. A total of 74 patients with metastatic renal cell carcinoma, referred to our institution to receive IL-2 from March 1989 to July 1991, were included in this prospective study. IL-2 was given on a 2-days-a-week schedule (24 x 10(6) IU m-2 day-1) either alone (41 patients) or in association with interferon gamma (33 patients). All these patients were prospectively evaluated for fever, bacteremia and line-site infection. Seven patients (9.5%) had one (2 patients) or more (5 patients) positive blood cultures with Staphylococcus aureus. Antibiotics were used only in 5 patients, and the catheter had to be removed in only 2 of these patients. In the other patients, no further infection developed despite the lack of antibiotics. Moreover, 9 patients had positive blood cultures with Staphylococcus epidermidis (1.9% of total number of blood cultures). In conclusion, a totally implanted catheter appears to reduce the incidence of infections in IL-2-treated patients, at least on a 2-days-a-week schedule.

Classical external indwelling central venous catheter versus totally implanted venous access systems for chemotherapy administration: a randomized trial in 100 patients with solid tumors.

A prospective randomized trial was organized at the Institut Gustave-Roussy to assess the reliability of classical external catheters (CE) versus totally implanted access systems (TI) for delivering intravenous chemotherapy for a duration of at least 6 months. The analysis was performed on the 96 patients whose implantation succeeded (CE 46, TI 50). Failure was defined as loss of ability to function (followed by removal) within the 6-month period of the survey. Patients dying with functional catheters were considered as censored (15 cases) at the time of death. Twenty-four access systems were removed. The removal-free curves differ significantly (P less than 0.001), favoring the TI access systems. The main reasons for removal were: catheter fall (CE6, (TI 0), migration (CE 1, TI 1), infection (CE 5, TI 1), thrombotic occlusion (CE 1, TI 0) and venous complications (CE 1 thrombosis plus 1 pulmonary embolism, TI 1 thrombosis). In addition, a survey by questionnaire demonstrated a significantly better patient activity rate (P = 0.02) and hygiene (P less than 0.001) in the TI group. This prospective randomized study demonstrates that totally implanted access systems are more reliable, safer and better tolerated than classical external catheters for solid tumor patients undergoing intravenous chemotherapy for longer than 6 months.

Phytohormone control of translatable RNA populations in sexual organogenesis of the dioecious plant Mercurialis annua L. (2n = 16).

A cell-free translation system was programmed with total, poly(A), non poly(A) and polysomal RNAs from male and female flowers of this plant with separated sexes. The peptide patterns obtained reflected differences in corresponding translatable RNAs. In total RNA products, three peptides were specific for males, two for females. One of the two male-specific polypeptides of high molecular weight was obtained from poly(A) RNAs and a female-specific one from non poly(A) RNAs. Differences between peptides common to both sexes reflected different concentrations of corresponding messengers. Similar results were obtained with polysomal RNAs. The male-specific RNAs were depending on high endogenous auxin concentrations while the female on active cytokinins. Cytokinin feminization of males induced the female-specific RNAs showing cytokinin action at pretranslational stages. Phytohormone roles are discussed.