Balancing of thermal lenses in enhancement cavities with transmissive elements.

Thermal lensing poses a serious challenge for the power scaling of enhancement cavities, in particular when these contain transmissive elements. We demonstrate the compensation of the lensing induced by thermal deformations of the cavity mirrors with the thermal lensing in a thin Brewster plate. Using forced convection to fine-tune the lensing in the plate, we achieve average powers of up to 160 kW for 250-MHz-repetition-rate picosecond pulses with a power-independent mode size. Furthermore, we show that the susceptibility of the cavity mode size to thermal lensing allows highly sensitive absorption measurements.

Megawatt-scale average-power ultrashort pulses in an enhancement cavity.

We investigate power scaling of ultrashort-pulse enhancement cavities. We propose a model for the sensitivity of a cavity design to thermal deformations of the mirrors due to the high circulating powers. Using this model and optimized cavity mirrors, we demonstrate 400 kW of average power with 250 fs pulses and 670 kW with 10 ps pulses at a central wavelength of 1040 nm and a repetition rate of 250 MHz. These results represent an average power improvement of one order of magnitude compared to state-of-the-art systems with similar pulse durations and will thus benefit numerous applications such as the further scaling of tabletop sources of hard x rays (via Thomson scattering of relativistic electrons) and of soft x rays (via high harmonic generation).

Analysis and suppression of parasitic processes in noncollinear optical parametric amplifiers.

The influence of parasitic processes on the performance of ultra-broadband noncollinear optical parametric amplifiers (NOPA's) is investigated for walk-off and non-walk-off compensating configurations. Experimental results with a white-light-seeded NOPA agree well with numerical simulations. The same model shows that 10% of the output energy of an amplified signal can be transferred into a parasitic second harmonic of the signal. These findings are supported by quantitative measurements on a few-cycle NOPA, where a few percent of the signal energy is converted to its second harmonic in the walk-off compensating case. This effect is reduced by an order of magnitude in the non-walk-off compensating configuration. A detailed study of the phase-matching conditions of the most common nonlinear crystals provides guidelines for designing NOPA systems.

Longitudinal assessment of mental development in infants with nonsyndromic craniosynostosis with and without cranial release and reconstruction.

The effect of cranial release and reconstruction on the mental development of infants with nonsyndromic craniosynostosis was evaluated. Longitudinal assessment of mental development for infants before and after cranial release and reconstruction and for infants not undergoing surgical treatment was obtained by using the mental scale of the Bayley Scales of Infant Development. Severity of anatomic craniofacial deformity, perinatal medical risk factors, and age at time of surgery also were investigated. None of the infants displayed mental retardation [Mental Development Index (MDI) score < 70] before or after cranial release and reconstruction. Scores ranged from borderline retardation to very superior following a normal distribution. Severity of anatomic craniofacial deformity and perinatal risk factors were unrelated to mental development. Cranial release and reconstruction did not affect mental development positively or negatively but did result in improvement of the original craniofacial deformity.