Saturated amplification of a collisionally pumped optical-field-ionization soft X-ray laser at 41.8 nm.

We report the first saturated amplification of an optical-field-ionization soft x-ray laser. The amplifying medium is generated by focusing a circularly polarized 330-mJ, 35-fs, 10-Hz Ti:sapphire laser system in a few-mm cell filled with xenon. A gain of 67 cm(-1) on the 4d(9)5p-4d(9)5d transition at 41.8 nm in Pd-like xenon and a gain-length product of 15 have been inferred at saturation. This source delivers about 5 x 10(9) photons per pulse. The influence of the pumping energy and the laser polarization on the lasing output are also presented.

Hot-electron distribution functions in a subpicosecond laser interaction with solid targets of varying initial gradient scale lengths.

We have studied the distribution function of the hot electrons produced during the interaction of a 120-fs, 60-mJ, 800-nm wavelength and a p-polarized laser pulse with bilayered Al/Fe targets. The main pulse interacts with a preformed plasma, obtained with a controlled prepulse, whose density gradient scale length has been measured. The electron distribution function is characterized by means of the Kalpha emission of the two materials of the target as a function of the Al-layer thickness. The low-energy region (<50 keV) of the hot-electron distribution function shows no dependency in shape on the gradient scale length, but only a variation in the total number of the generated electrons. The comparison between the experimental results and the particle-in-cell and Monte Carlo calculations of the electron distribution function and the Kalpha emission is gratifying.

Ventral hernia repair with simultaneous panniculectomy.

The repair of a ventral hernia in an obese patient presents an interesting clinical challenge. We retrospectively reviewed the charts of 55 patients who, over a 12-year period from 1983 to 1995, concomitantly underwent both ventral herniorrhaphy and panniculectomy or abdominoplasty. In six of 55 patients, the hernia was recurrent. Forty-six patients had primary abdominal wall hernias or diastasis recti. Nineteen of 55 patients had weight greater than 200 lbs. This last subset of patients had a significantly higher incidence of complications, such as seroma, cellulitis, and persistent wound drainage. In our 55 patients, we experienced only two hernia recurrences (3.6%) during an average patient follow-up of 53 weeks. From this experience, we believe that simultaneous ventral hernia repair and panniculectomy is a safe and efficacious approach to these two problems so commonly found in the obese patient. Patients with a preoperative weight greater than 200 lbs can be expected to have a greater risk of wound complications. In all cases, the wounds eventually healed with no long-term sequelae.

Generation of 25-TW, 32-fs pulses at 10 Hz.

We have developed a femtosecond laser chain that generates 25-TW pulses of less than 35 fs at 10 Hz with focused intensities higher than 5 x 10(19) W/cm(2) and an average power of 8 W. This system is optimized for a broad transmission bandwidth and includes an aberration-free stretcher compressor.

Effects of a modified Q-switched Nd-YAG laser on human vascular tissue: an ex vivo study.

RATIONALE AND OBJECTIVES: Relatively disappointing results with continuous-wave lasers stimulated us to evaluate pulsed lasers for interventional radiology. In this article, we describe our efforts to assess the effects of this technology ex vivo. METHODS: We modified a Q-switched yttrium aluminum garnet (Nd-YAG) laser to emit pulses of 300 mJ maximum with a 20-Hz repetition rate, at 1064 nm, and with a duration that ranged from 300 ns to 2.3 microseconds. The lengthening of the pulse duration by a factor of 100 (compared with the conventional nanosecond Q-switched Nd-YAG laser) and the ability to define it exactly were obtained by controlling the opening and closing of the Pockels cell electronically. Lengthening the pulse duration made it possible to reduce peak power while conserving the same total energy. In this way, high energy was transmitted through thin optical fibers. RESULTS: One hundred fifty millijoules with 2-microsecond pulses, 140 mJ with 1-microsecond pulses, and 100 mJ with 500-ns pulses were transmitted through a 300-micron silica-polymer fiber. The transmission coefficient was identical for the three pulse durations. Ex vivo irradiation experiments were performed on human atheromatous arteries in saline solution using a 300-micron diameter optical fiber. Craters were easily obtained. Their depth and width were related to maximum energy transmission and irradiation time. No carbonization occurred and no destruction of the optical fiber was observed. CONCLUSION: A modified Q-switched Nd-YAG laser can transmit high-energy pulses through thin optical fibers without damaging them and can destroy human atheroma in an ex vivo setting.

Frequency-domain interferometer for measuring the phase and amplitude of a femtosecond pulse probing a laser-produced plasma.

A frequency-domain interferometer for probing the variations of the dielectric constant of a plasma with sub-100- fs temporal resolution and lambda/2000 phase resolution is described. Imaging the plasma on the entrance slit of a spectrograph provides spatial resolution along a diameter of the focal spot. The technique is used to map out the expansion of the critical density surface of a femtosecond laser-produced plasma with subnanometer spatial resolution along the laser axis.

Compact and efficient multipass Ti:sapphire system for femtosecond chirped-pulse amplification at the terawatt level.

We have developed efficient multipass Ti:sapphire amplifiers for femtosecond chirped-pulse amplification. With only two of these devices we get an amplification factor of 10(8), which corresponds to a peak power of ~0.5 TW after compression. We present a detailed analysis of such a system and its advantages in terms of its high quantum yield (0.3), flexibility, optical quality, and potential for tunability.