Precise parameter control of multicycle terahertz generation in PPLN using flexible pulse trains.

The low (sub %) efficiencies so-far demonstrated for nonlinear optical down-conversion to terahertz (THz) frequencies are a primary limiting factor in the generation of high-energy, high-field THz-radiation pulses (in particular narrowband, multicycle pulses) needed for many scientific fields. However, simulations predict that far higher conversion efficiencies are possible by use of suitably-optimized optical sources. Here we implement a customized optical laser system producing highly-tunable trains of infrared pulses and systematically explore the experimental optimization of the down-conversion process. Our setup, which allows tuning of the energy, duration, number and periodicity of the pulses in the train, provides a unique capability to test predictions of analytic theory and simulation on the parameter dependences for the optical-to-THz difference-frequency generation process as well as to map out, with unprecedented precision, key properties of the nonlinear crystal medium. We discuss the agreements and deviations between simulation and experimental results which, on the one hand, shed light on limitations of the existing theory, and on the other hand, provide the first steps in a recipe for development of practical, high-field, efficiency-optimized THz sources.

One-joule 500-Hz cryogenic Yb:YAG laser driver of composite thin-disk design.

We present results on the development of a cryogenic Yb:YAG multi-pass laser amplifier based on a composite thin-disk design and demonstrate one-joule, diffraction limited, chirped 234-ps pulses with 50% optical-to-optical efficiency. High beam quality was obtained for repetition rates up to 400 Hz. The hardware was disassembled and thoroughly inspected after accumulating 80 hours of use at repetition rates from 100 to 500 Hz and exhibited no signs of damage. This laser driver is now commissioned to a dedicated laboratory where a grating compressor is producing 5.2-ps pulses used in the development of a compact x ray source based on inverse Compton scattering.

Highly efficient generation of narrowband terahertz radiation driven by a two-spectral-line laser in PPLN.

We demonstrate record ∼0.9% efficiencies for optical conversion to narrowband (<1% relative bandwidth) terahertz (THz) radiation by strongly cascaded difference frequency generation. These results are achieved using a novel, to the best of our knowledge, laser source, customized for high efficiencies, with two narrow spectral lines of variable separation and pulse duration (≥250 ps). THz radiation generation in 5% MgO-doped periodically poled lithium niobate (PPLN) crystals of varying poling period was explored at cryogenic and room temperature operation as well as with different crystal lengths. This work addresses an increasing demand for high-field THz radiation pulses which has, up to now, been largely limited by low optical-to-THz radiation conversion efficiencies.

Versatile optical laser system for experiments at the European X-ray free-electron laser facility.

We present the main features of the final prototype of a pulsed optical laser, developed for pump-probe and other experiments in conjunction with the femtosecond x-ray beams at the European X-ray free-electron laser facility. Adapted to the temporal x-ray emission pattern of the facility, the laser provides 10 Hz bursts of up to 600 µs duration with intra-burst pulse frequencies as high as 4.5 MHz. In this mode, we have generated pulses as short as 12 fs at 350 W average power during the burst and with beam qualities close to the diffraction limit. This is, to the best of our knowledge, the highest power to date of a few-cycle laser operating at a center wavelength of 800 nm. Important for experimental flexibility, the laser can be configured in various unique ways, enabling, e.g., energy scaling to >3 mJ per pulse through a frequency change down to 100 kHz and the generation of nearly transform limited pulses between 12 fs and 300 fs. In addition to the 800 nm femtosecond beam line, a synchronized long pulse (0.8 ps or 400 ps) 1030 nm beam can be utilized, offering up to 4 kW burst average power, i.e. up to 40 mJ per pulse at 100 kHz. Efficient nonlinear wavelength conversion and tuning through intrinsic and external means further enhance the capabilities of the laser.

High power burst-mode optical parametric amplifier with arbitrary pulse selection.

We present results from a unique burst-mode femtosecond non-collinear optical parametric amplifier (NOPA) under development for the optical - x-ray pump-probe experiments at the European X-Ray Free-Electron Laser Facility. The NOPA operates at a burst rate of 10 Hz, a duty cycle of 2.5% and an intra-burst repetition rate of up to 4.5 MHz, producing high fidelity 15 fs pulses at a center wavelength of 810 nm. Using dispersive amplification filtering of the super-continuum seed pulses allows for selectable pulse duration up to 75 fs, combined with a tuning range in excess of 100 nm whilst remaining nearly transform limited. At an intra-burst rate of 188 kHz the single pulse energy from two sequential NOPA stages reached 180 µJ, corresponding to an average power of 34W during the burst. Acousto- and electro-optic switching techniques enable the generation of transient free bursts of required length and the selection of arbitrary pulse sequences inside the burst.

Cystic renal lymphangiectasia: a distinctive clinicopathologic entity in the pediatric age group.

This report describes the features of unilateral cystic renal lymphangiectasia in a 2-year-old child who presented with hypertension, massive ascites, a left flank mass, and no evidence of familial renal cystic disease. The child became normotensive and is now asymptomatic more than 3 years after surgery. The clinical presentation and diffuse pathologic involvement are similar to findings for the few pediatric patients with cystic lymphangiectasia described in the literature and appear distinct from the more localized form of the disease seen in adults.

Choice of an optimum multichannel Nd:glass laser system for fusion experiments.

A comparison has been made between proposed configurations for Nd-glass laser systems for fusion. Detailed theoretical modeling of pulse propagation has been carried out using a linearized model with the variables taken to be time, axial coordinate, and one transverse coordinate. A non-temporally varying, three-spatial dimension model was also used to correct the linearized two-spatial dimension calculations. A 10(5) J system using 200 slab amplifiers and 20 spatial filters and having a 10(-4) rad divergence appears feasible.

Disseminated intravascular coagulation in the urologic patient.

Gram-negative septicemia and metastatic prostatic cancer are frequent causes of disseminated intravascular coagulation. The clinical manifestations of this condition as well as the laboratory data vary considerably, depending on the patient's compensatory mechanisms in relation to the magnitude and duration of the thromboplastin or endotoxin release. Treatment centers primarily on correcting the underlying disorder. Secondly, deficient clotting factors and platelets should be replaced in the appropriate patient. Heparinization is often unnecessary. The use of drugs that inhibit the protective fibrinolytic mechanism is contraindicated in disseminated intravascular coagulation.

High power output stages of a Nckglass laser system for fusion applications.

This short paper considers the advantages and disadvantages of active element apertures in the form of disks and long rectangular cross-section slabs used in laboratories in the U.S.A. and the U.S.S.R.