Perturbative study of multiphoton processes in the tunneling regime

A perturbative study of the Schr\"{o}dinger equation in a strong electromagnetic field with dipole approximation is accomplished in the Kramers-Henneberger frame. A prove that just odd harmonics appear in the spectrum for a linear polarized laser field is given, assuming that the atomic radius is much lesser than the free-electron quiver motion amplitude. Within this approximation a perturbation series is obtained in the Keldysh parameter giving a description of multiphoton processes in the tunneling regime. The theory is applied to the case of hydrogen-like atoms: The spectrum of higher order harmonics and the above-threshold ionization rate are derived. The ionization rate computed in this way determines the amplitudes of the harmonics. The wave function of the atom proves to be rigid with respect to the perturbation so that the effect of the laser field on the Coulomb potential in the computation of the probability amplitudes can be neglected as a first approximation: This approximation improves as the ratio between the amplitude of the quiver motion of the electron and the atom radius becomes larger. The semiclassical description currently adopted for harmonic generation is so rederived by solving perturbatively the Schr\"{o}dinger equation.Comment: Latex, 11 pages. To appear on Phys. Lett.

Generation of chirp-free picosecond pulses

The frequency spectrum of moderately chirped laser pulses depends upon the portion of the beam which is accepted by the spectrometer. Observation of the development of the chirp in a mode-locked pulse train allows to determine the small incipient chirp of early pulses. A product, bandwidth times pulse duration, of 0.47 ± 0.03 is consistently observed for single pulses switched from a passively mode-locked Nd-glass system

Second harmonic beam analysis, a sensitive technique to determine the duration of single ultrashort laser pulses

The second harmonic beam generated in a noncollinear arrangement allows the observation of the autocorrelation functio: A compact optical beam splitter and imaging system eliminates alignment problems. Single pulses of 1 ps duration and approximately 10−8 joule energy are readily observed using an optical multichannel analyser

Terahertz quantum beats in molecular liquids

With ultrashort pulses of less than 100 fs it is possible to excite coherently several vibrational modes of polyatomic molecules simultaneously. The femtosecond time resolution of the experiment allows the study of pronounced high-frequency beat phenomena up to 10 THz. The frequency difference between vibrational modes separated by more than 300 cm−1 may be determined with high precision

Platelets are key in cold physical plasma-facilitated blood coagulation in mice

Purpose: Surgical interventions inevitably lead to destruction of blood vessels. This is especially dangerous in anticoagulated patients. Electrocauterization is a frequently used technique to seal incised tissue. However, leading to a superficial layer of necrotic tissue, the treated area evolves a high vulnerability to contact, making it prone to detachment. As a result, dangerous postoperative bleeding may occur. Cold physical plasma was previously suggested as a pro-coagulant treatment method. It mainly acts by expelling a delicate mixture of oxidants. We therefore tested the suitability of an atmospheric pressure plasma jet (kINPen MED) as a new medical device for sufficient blood coagulation in a murine model of liver incision. Methods: Plasma treatment of murine blood ex vivo induced sufficient coagula. This effect did not affect any tested parameter of plasmatic coagulation cascade, suggesting the mechanism to be related to cellular coagulation. Indeed, isolated platelets were significantly activated following exposure to plasma, although this effect was less pronounced in whole blood. To analyze the biological effect of plasma-on blood coagulation in vivo, mice were anticoagulated (clopidogrel inhibiting cellular and rivaroxaban inhibiting plasmatic hemostasis) or received vehicle only. Afterwards, a partial resection of the left lateral liver lobe was performed. The quantification of the blood loss after liver incision followed by treatment with kINPen MED plasma or electrocauterization revealed a similar and significant hemostatic performance in native and rivaroxaban but not clopidogrel-treated animals compared to argon gas-treated controls. In contrast to electrocauterization, kINPen MED plasma treatment did not cause necrotic cell layers. Conclusion: Our results propose a prime importance of platelets in cold physical plasma-mediated hemostasis and suggest a clinical benefit of kINPen MED plasma treatment as coagulation device in liver surgery