A nozzle for high-density supersonic gas jets at elevated temperatures.

We present the development of a gas nozzle providing high-density gas at elevated temperatures inside a vacuum environment. Fused silica is used as the nozzle material to allow the placement of the nozzle tip in close proximity to an intense, high-power laser beam, while minimizing the risk of sputtering nozzle tip material into the vacuum chamber. Elevating the gas temperature increases the gas-jet forward velocity, allowing us to replenish the gas volume in the laser-gas interaction region between consecutive laser shots. The nozzle accommodates a 50 µm opening hole from which a supersonic gas jet emerges. Heater wires are used to bring the nozzle temperature up to 730 °C, while a cooling unit ensures that the nozzle mount and the glued nozzle-to-mount connection is kept at a temperature below 50 °C. The presented nozzle design is used for high-order harmonic generation in hot gases using gas backing pressures of up to 124 bars.

Attosecond time-resolved photoelectron holography.

Ultrafast strong-field physics provides insight into quantum phenomena that evolve on an attosecond time scale, the most fundamental of which is quantum tunneling. The tunneling process initiates a range of strong field phenomena such as high harmonic generation (HHG), laser-induced electron diffraction, double ionization and photoelectron holography-all evolving during a fraction of the optical cycle. Here we apply attosecond photoelectron holography as a method to resolve the temporal properties of the tunneling process. Adding a weak second harmonic (SH) field to a strong fundamental laser field enables us to reconstruct the ionization times of photoelectrons that play a role in the formation of a photoelectron hologram with attosecond precision. We decouple the contributions of the two arms of the hologram and resolve the subtle differences in their ionization times, separated by only a few tens of attoseconds.

Attosecond-resolved photoionization of chiral molecules.

Chiral light-matter interactions have been investigated for two centuries, leading to the discovery of many chiroptical processes used for discrimination of enantiomers. Whereas most chiroptical effects result from a response of bound electrons, photoionization can produce much stronger chiral signals that manifest as asymmetries in the angular distribution of the photoelectrons along the light-propagation axis. We implemented self-referenced attosecond photoelectron interferometry to measure the temporal profile of the forward and backward electron wave packets emitted upon photoionization of camphor by circularly polarized laser pulses. We measured a delay between electrons ejected forward and backward, which depends on the ejection angle and reaches 24 attoseconds. The asymmetric temporal shape of electron wave packets emitted through an autoionizing state further reveals the chiral character of strongly correlated electronic dynamics.

Central nervous system lymphomas in organ allograft recipients.

Central nervous system (CNS) involvement occurred in 289 of 1332 patients (22%) with posttransplant non-Hodgkins lymphomas. The average time of appearance was 33 months (range 3 weeks to 248.5 months) posttransplantation. Lesions were confined to the CNS in 159 patients (55%), while 130 (45%) had involvement of other organs. Lesions involved the brain in 254 patients (88%), the brain and spinal cord in 5 (2%), the spinal cord in 2 (1%), unspecified locations in the CNS in 13 (4%), the meninges in 8 (3%), and the cerebrospinal fluid (CSF) in 7 (2%). All patients whose only involvement of the CNS was of the meninges or CSF had lymphomas involving multiple organs. Many tumors (48%) appeared within one year after transplantation. Brain lesions were frequently multicentric in distribution. Ninety-one (31%) of the 289 patients had no treatment and died, 70 (77%) of their malignancies and 21 (23%) from other causes. Of 198 patients who received treatment 124 (63%) died of their malignancies; 40 (20%) died of other causes, including 17 patients who had had complete remissions following treatment; 22 (11%) are currently alive and in complete remission; and 12 (6%) are alive and still undergoing therapy. The treatment of choice is local radiotherapy to the brain, which either alone (18 patients) or in combination with other modalities (14 patients) caused 32 of the 39 (82%) complete remissions. Ten of 30 patients with disease localized to the CNS survived more than 5 years, including 6 who survived more than 10 years. CNS lymphomas should be suspected whenever a transplant patient has neurologic symptoms however minor, and prompt work-up is essential to eliminate other possible causes. The dismal prognosis can be improved only by early diagnosis and prompt therapy.