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Biomedical subjects

C Spielmann

Publications and source records attributed to C Spielmann.

11 recordsLinked to original sources
PubMed2005

Laser technology: source of coherent kiloelectronvolt X-rays.

Generating X-rays that have the properties of laser light has been a long-standing goal for experimental science. Here we describe the emission of highly collimated, spatially coherent X-rays, at a wavelength of about 1 nanometre and at photon energies extending to 1.3 kiloelectronvolts, from atoms that have been ionized by a 5-femtosecond laser pulse. This means that a laboratory source of laser-like, kiloelectronvolt X-rays, which will operate on timescales relevant to many chemical, biological and materials problems, is now within reach.

Journal Article↗
PubMed2001

Attosecond metrology.

The generation of ultrashort pulses is a key to exploring the dynamic behaviour of matter on ever-shorter timescales. Recent developments have pushed the duration of laser pulses close to its natural limit-the wave cycle, which lasts somewhat longer than one femtosecond (1 fs = 10-15 s) in the visible spectral range. Time-resolved measurements with these pulses are able to trace dynamics of molecular structure, but fail to capture electronic processes occurring on an attosecond (1 as = 10-18 s) timescale. Here we trace electronic dynamics with a time resolution of </= 150 as by using a subfemtosecond soft-X-ray pulse and a few-cycle visible light pulse. Our measurement indicates an attosecond response of the atomic system, a soft-X-ray pulse duration of 650 +/- 150 as and an attosecond synchronism of the soft-X-ray pulse with the light field. The demonstrated experimental tools and techniques open the door to attosecond spectroscopy of bound electrons.

Journal Article↗
PubMed2001

X-ray pulses approaching the attosecond frontier.

Single soft-x-ray pulses of approximately 90-electron volt (eV) photon energy are produced by high-order harmonic generation with 7-femtosecond (fs), 770-nanometer (1.6 eV) laser pulses and are characterized by photoionizing krypton in the presence of the driver laser pulse. By detecting photoelectrons ejected perpendicularly to the laser polarization, broadening of the photoelectron spectrum due to absorption and emission of laser photons is suppressed, permitting the observation of a laser-induced downshift of the energy spectrum with sub-laser-cycle resolution in a cross correlation measurement. We measure isolated x-ray pulses of 1.8 (+0.7/-1.2) fs in duration, which are shorter than the oscillation cycle of the driving laser light (2.6 fs). Our techniques for generation and measurement offer sub-femtosecond resolution over a wide range of x-ray wavelengths, paving the way to experimental attosecond science. Tracing atomic processes evolving faster than the exciting light field is within reach.

Journal Article↗
PubMed2000

Femtosecond X-Ray fluorescence

Using few-cycle-driven coherent laser harmonics, K-shell vacancies have been created in light elements, such as boron (E(B) = 188 eV) and carbon (E(B) = 284 eV), on a time scale of a few femtoseconds for the first time. The capability of detecting x-ray fluorescence excited by few-femtosecond radiation with an accuracy of the order of 1 eV paves the way for probing the evolution of the microscopic environment of selected atoms in chemical and biochemical reactions on previously inaccessible time scales (<100 fs) by tracing the temporal evolution of the "chemical shift" of peaks associated with inner-shell electronic transitions in time-resolved x-ray fluorescence and photoelectron spectra.

Journal Article↗
PubMed2000

Controlling the phase evolution of few-cycle light pulses

Using a coherent nonlinear optical technique, slipping of the carrier through the envelope of 6-fs light wave packets emitted from a mode-locked-oscillator/pulse-compressor system has been measured, permitting the generation of intense, few-cycle light with precisely reproducible electric and magnetic fields. These pulses open the way to controlling the evolution of strong-field interactions on the time scale of the light oscillation cycle and are indispensable to reproducible attosecond x-ray pulse generation.

Journal Article↗
PubMed1999

[Etiology and prophylaxis of reperfusion injuries].

In recent years the importance of oxyradicals in clinical veterinary medicine is incessantly grown. An important example in cattle breeding is the displaced abomasum in dairy cows. The antioxidative status of the animals is representable by means of the activity of superoxide dismutase (SOD) in the blood. Post operationem the activity of SOD decreased very fast. In cows with left abomasal displacement this activity increased within 24 hours to the starting level, but in cows with right abomasal displacement the SOD-activity in this period increased only insignificantly. Because of the low level of SOD-activity in blood serum the measuring should take place in erythrocyte lysate. Today there are many possibilities of therapeutical intervention of reperfusion injury, but their clinical efficiency has to be ascertained. The treatment of cows with displaced abomasum with ascorbate, tocopherole or prednisolone before the replacement of the abomasum shows first success in terms of the antioxidative and metabolic status.

Abomasum↗
PubMed1990

[Computer-assisted analysis of pressure distribution on cattle claws].

A newly developed measuring device was applied to quantify in 5 first and 5 second lactation cows of the breed German Black and White the pressure distribution underneath the claws of one front limb. The pressure distribution of cows was recorded five times in intervals of four weeks. At each measuring date each had to undergo three tests. Procedures for image processing were applied in analysis of pressure distributions. The average pressure per sqcm was about 19 N, the maximum pressure measured was 59 N per sqcm in first lactating cows and 56 N per sqcm in second lactation cows. Factors were developed which characterize the patterns of pressure distributions. Especially the "gradient factor" seems to be well suited to recognize inhomogeneous pressure distributions.

Animals↗