Guiding of laser pulses in plasma waveguides created by linearly-polarized femtosecond laser pulses

We experimentally demonstrate that plasma waveguides produced with ultra-short laser pulses (sub-picosecond) in gas jets are capable of guiding high intensity laser pulses. This scheme has the unique ability of guiding a high-intensity laser pulse in a plasma waveguide created by the same laser system in the very simple and stable experimental setup. A hot plasma column was created by a femtosecond class laser that expands into an on-axis parabolic low density profile suitable to act as a waveguide for high intensity laser beams. We have successfully guided ~10¹⁵ W cm⁻² laser pulses in a 8 mm long hydrogen plasma waveguide with a 35% guiding efficiency.

Dispersion compensation by two-stage stretching in a sub-400 fs, 1.2 mJ Yb:CaF2 amplifier

We generate 1.24 mJ, 390 fs pulses at 1035 nm in a CPA laser system featuring a 2.8 mJ Yb:CaF(2) regenerative amplifier, stretcher/compressor based on a single chirped volume Bragg grating and a compact, low-dispersion grating compressor. The auxiliary compressor is used to effectively pre-compensate the intra-cavity dispersion of the amplifier.

Laparoscopic surgery and corticoadrenalomas

BACKGROUND

Nowadays, laparoscopic adrenalectomy is the "gold standard" procedure for the treatment of benign lesions. However, the situation is not so clearcut when the issue is laparoscopic excision of malignant adrenal tumors. We present our results of laparoscopic adrenalectomy for treating malignant tumors over the past decade.

METHODS

Between October 1995 and June 2004, 131 consecutive laparoscopic adrenalectomies were performed on 120 patients (11 synchronous bilateral procedures). All patients underwent a standardized investigation protocol during their workup for surgery.

RESULTS

There were only two conversions to laparotomy (1.6%). Complications that occurred during the procedure were limited to six patients (5%). Postoperative 30-days mortality was nil. Postoperative complications occurred in five patients (4.7%) during the first 30 days of recovery. The median hospital stay for all patients was 2.5 days (range = 2-10 days). Twelve patients (9%) had a malignant tumor: nine corticoadrenalomas, one pleomorphic sarcoma, one metastatic deposit from a previously excised colonic cancer, and one malignant pheochromocytoma. At mean followup of 34 months, mean survival time was 42.3 months for corticoadrenalomas that had undergone laparoscopy versus 29.7 months for those who had had a laparotomy. Five of the nine patients are alive and well at a mean of 37 months following surgery. One patient developed pulmonary metastases one year postsurgery; they were responsive to mitotane. Five years later, the same patient had a reoperation for an intra-abdominal retrogastric recurrence of her tumor and continues to do well. Another patient developed pulmonary metastases 22 months following adrenalectomy. Two patients died of metastatic intra-abdominal disease 20 and 7 months postsurgery.

CONCLUSION

When laparoscopic surgery is to used for cancer treatment, caution is the rule to maintain the primary objective of securing a survival rate at least as high as that for open surgery, without increased risk of recurrence. Considering the results presented within this study, it seems that the laparoscopic removal of a corticoadrenaloma should not worsen the prognosis, provided the surgeon respects the primary rules of oncologic resectional surgery. Any surgical conditions that would preclude the strict application of these criteria are contraindications to a laparoscopic procedure.

Plasma channels produced by a laser-triggered high-voltage discharge

A plasma waveguide scheme for high-intensity laser guiding with densities and lengths suitable for laser-plasma particle accelerators is presented. This scheme uses a laser-triggered high-voltage discharge, presents negligible jitter, allows full access to the plasma, and can be scaled to large distances. Experimental results showing the feasibility of this scheme are presented.

Photon acceleration of ultrashort laser pulses by relativistic ionization fronts

We present experimental results from the collision of weak ultrashort pulses with relativistic ionization fronts in copropagation and counterpropagation. The observed frequency upshifts of the probe pulses provide not only information about the electron density of the ionization front but also reveal the fine structure of the front. The connection between the correlation lengths for copropagation and counterpropagation and the longitudinal and transverse dimensions of the ionization front is also demonstrated thus showing the feasibility of using the frequency upshift experienced by short probe pulses to fully characterize relativistic ionization fronts and other relativistic coherent structures in laser-produced plasmas.

Two-dimensional collision of probe photons with relativistic ionization fronts

The collision of a probe laser pulse with a relativistic ionization front is analyzed via two-dimensional ray-tracing theory and simulations. It is shown that collisions in higher dimensions lead to new regimes for the frequency upshift of the probe photons; the frequency upshift can be considerably higher for particular collision angles that maximize the interaction length with the ionization front gradient. Finite ionization fronts also lead to angle-dependent frequency upshifts, thus acting as diffraction gratings.