An adaptive optics system for solid-state laser systems used in inertial confinement fusion

Using adaptive optics the authors have obtained nearly diffraction-limited 5 kJ, 3 nsec output pulses at 1.053 {micro}m from the Beamlet demonstration system for the National Ignition Facility (NIF). The peak Strehl ratio was improved from 0.009 to 0.50, as estimated from measured wavefront errors. They have also measured the relaxation of the thermally induced aberrations in the main beam line over a period of 4.5 hours. Peak-to-valley aberrations range from 6.8 waves at 1.053 {micro}m within 30 minutes after a full system shot to 3.9 waves after 4.5 hours. The adaptive optics system must have enough range to correct accumulated thermal aberrations from several shots in addition to the immediate shot-induced error. Accumulated wavefront errors in the beam line will affect both the design of the adaptive optics system for NIF and the performance of that system

NIF pointing and centering systems and target alignment using a 351 nm laser source

The operational requirements of the National Ignition Facility (NIF) place tight constraints upon its alignment system. In general, the alignment system must establish and maintain the correct relationships between beam position, beam angle, laser component clear apertures, and the target. At the target, this includes adjustment of beam focus to obtain the correct spot size. This must be accomplished for all beamlines in a time consistent with planned shot rates and yet, in the front end and main laser, beam control functions cannot be initiated until the amplifiers have sufficiently cooled so as to minimize dynamic thermal distortions during and after alignment and wavefront optimization. The scope of the task dictates an automated system that implements parallel processes. We describe reticle choices and other alignment references, insertion of alignment beams, principles of operation of the Chamber Center Reference System 2048 and Target Alignment Sensor, and the anticipated alignment sequence that will occur between shots

Air temperature in Novaya Zemlya Archipelago and Vaygach Island from 1832 to 1920 in the light of early instrumental data

In this article, the results of an investigation into the air temperature conditions in Novaya Zemlya Archipelago and Vaygach Island (NZR) from 1832 to 1920, on the basis of all available early instrumental data gathered during exploratory and scientific expeditions, are presented. Traditional analysis based on mean monthly data was supplemented by an approach less popular in the scientific literature, i.e. the additional use of daily data. Moreover, the daily data used were not limited only to mean daily air temperature, but include also maximum daily temperature, minimum daily temperature and diurnal temperature range. Such rich sets of data allowed for more comprehensive and precise recognition of air temperature conditions in the NZR. Based on these kinds of daily data, it was also possible to calculate the number of so-called ‘characteristic days’ (i.e. the number of days with temperatures exceeding specified thresholds) and day-to-day temperature variability and, for the first time, to determine different characteristics of thermal seasons (duration, onset and end dates) according to Baranowski's (1968) proposition. The results were compared with contemporary temperature conditions (1981–2010) to estimate the range of their changes between historical and present times. Analysis reveals that in 1832–1920, the NZR was markedly colder than today in all seasons. Coldest was autumn (on average by ca 5 °C), and least – summer (by 1.6 °C). Mean annual air temperature was colder than today by about 3 °C. The majority of mean monthly air temperatures in historical times lie within two standard deviations from the modern mean. This means that values of air temperature in historical times lie within the range of contemporary air temperature variability. Different air temperature characteristics calculated on the basis of daily data for the NZR for historical/contemporary periods also confirm the occurrence of climate warming between the studied periods

The National Ignition Facility (NIF) Wavefront Control System

A wavefront control system will be employed on NIF to correct beam aberrations that otherwise would limit the minimum target focal spot size. For most applications, NIF requires a focal spot that is a few times the diffraction limit. Sources of aberrations that must be corrected include prompt pump-induced distortions in the laser slabs, thermal distortions in the laser slabs from previous shots, manufacturing figure errors in the optics, beam off-axis effects, gas density variations, and gravity, mounting, and coating- induced optic distortions. The NIF Wavefront Control System consists of five subsystems: 1) a deformable mirror, 2) a wavefront sensor, 3) a computer controller, 4) a wavefront reference system, and 5) a system of fast actuators to allow the wavefront control system to operate to within one second of the laser shot. The system includes the capability for in situ calibrations and operates in closed loop prior to the shot. Shot wavefront data is recorded. This paper describes the function, realization, and performance of each wavefront control subsystem. Subsystem performance will be characterized by computer models and by test results. The focal spot improvement in the NIF laser system effected by the wavefront control system will be characterized through computer models

Geschichte Masurens; ein Beitrag zur preussischen Landes- und Kulturgeschichte. Nach gedruckten und ungedruckten Quellen.

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