Non-linear optical frequency conversion crystals for space applications

Reliable, long term operation of high-power laser systems in the Earth orbit is not a straightforward task as the space environment entails various risks for optical surfaces and bulk materials. The increased operational risk is, among others, due to the presence of high energy radiation penetrating the metallic shielding of satellites and inducing absorption centers in the bulk of optical components, and vacuum exposure which can deteriorate coating performance. Comprehensive testing for analyzing high-energy radiation effects and mitigation procedures were performed on a set of frequency conversion crystals and are discussed in this paper. In addition to a general resistance to space environmental effects, the frequency conversion crystals were subjected to a comparative analysis on optimum third harmonic efficiency, starting from pulsed 1064 nm laser radiation, with the goal of exceeding a value of 30 %. Concomitant modeling supported the selection of crystal parameters and the definition of crystal dimensions

AKTIP/Ft1, a new shelterin-interacting factor required for telomere maintenance

Telomeres are nucleoprotein complexes that protect the ends of linear chromosomes from incomplete replication, degradation and detection as DNA breaks. Mammalian telomeres are protected by shelterin, a multiprotein complex that binds the TTAGGG telomeric repeats and recruits a series of additional factors that are essential for telomere function. Although many shelterin-associated proteins have been so far identified, the inventory of shelterin-interacting factors required for telomere maintenance is still largely incomplete. Here, we characterize AKTIP/Ft1 (humanAKTIP and mouse Ft1 are orthologous), a novel mammalian shelterin-bound factoridentified on the basis of its homology with the Drosophila telomere protein Pendolino. AKTIP/Ft1 shares homology with the E2 variant ubiquitin-conjugating (UEV) enzymes and has been previously implicated in the control of apoptosis and in vesicle trafficking. RNAi-mediated depletion of AKTIP results in formation of telomere disfunction foci (TIFs). Consistent with these results, AKTIP interacts with telomeric DNA and binds the shelterin components TRF1 and TRF2 both in vivo and in vitro. Analysis of AKTIP- depleted human primary fibroblasts showed that they are defective in PCNA recruiting and arrest in the S phase due to the activation of the intra S checkpoint. Accordingly, AKTIP physically interacts with PCNA and the RPA70 DNA replication factor. Ft1-depleted p53-/- MEFs did not arrest in the S phase but displayed significant increases in multiple telomeric signals (MTS) and sister telomere associations (STAs), two hallmarks of defective telomere replication. In addition, we found an epistatic relation for MST formation between Ft1 and TRF1, which has been previously shown to be required for replication fork progression through telomeric DNA. Ch-IP experiments further suggested that in AKTIP-depleted cells undergoing the S phase, TRF1 is less tightly bound to telomeric DNA than in controls. Thus, our results collectively suggest that AKTIP/Ft1 works in concert with TRF1 to facilitate telomeric DNA replication

Investigation of laser-induced ablation of ceramic materials for spaceborne applications

In this work tests for determination of ablation thresholds of various ceramic materials for pulsed laser irradiations at wavelengths of 355 nm and 1064 nm in vacuum are presented. For comparison tests with copper and aluminium are also reported. The ablation process was monitored insitu by long-distance microscopy. The morphology of ablation spots was exsitu inspected by scanning electron microscopy. Furthermore, the redeposition of potentially released particles on optics in the vicinity to the target was examined

Spatially resolved transcriptomics reveals innervation-responsive functional clusters in skeletal muscle

Striated muscle is a highly organized structure composed of well-defined anatomical domains with integrated but distinct assignments. So far, the lack of a direct correlation between tissue architecture and gene expression has limited our understanding of how each unit responds to physio-pathologic contexts. Here, we show how the combined use of spatially resolved transcriptomics and immunofluorescence can bridge this gap by enabling the unbiased identification of such domains and the characterization of their response to external perturbations. Using a spatiotemporal analysis, we follow changes in the transcriptome of specific domains in muscle in a model of denervation. Furthermore, our approach enables us to identify the spatial distribution and nerve dependence of atrophic signaling pathway and polyamine metabolism to glycolytic fibers. Indeed, we demonstrate that perturbations of polyamine pathway can affect muscle function. Our dataset serves as a resource for future studies of the mechanisms underlying skeletal muscle homeostasis and innervation

Harmonisation of two nanosecond laser induced damage testing facilities at 1064 nm in vacuum and ambient pressure

In this paper we will discuss the difficulties of performing comparable laser damage testing as well as a detailed analysis of the measurements conducted on the samples for this harmonisation activity. Four samples have been compared with the S-on-1 method according to ISO21254-1, two AR1064/0° windows and two silicon wafer. The total variation of the 0% damage probability values after 10000 shots is less than 20%, which is well within the 2σ uncertainty, both laboratories calculate individually. The obtained level of agreement is, to our best knowledge, the closest for two ISO21254-1 nanosecond laser induced damage threshold testing facilities reported

Verification for robustness to laser-induced damage for the Aladin instrument on the ADM-Aeolus satellite

The Aladin instrument will fly on the European Space Agency’s ADM Aeolus satellite. The instrument is a Doppler wind LIDAR, primarily designed to measure global wind profiles to improve the accuracy of numerical weather prediction models. At the heart of the instrument is a frequency stabilized 355nm laser which will emit approximately 100mJ of energy in the form of 20ns pulses with a fluence around 1Jcm-2. The pulse repetition frequency is 50Hz meaning that Aladin will eventually have to accumulate 5Gshots over its 3 year planned lifetime in orbit. Due to anomalies that have occurred on previous space-borne lasers, as well as a number of failures that we have observed in previous tests, an extensive development and verification campaign was undertaken in order to ensure that the Aladin instrument is robust enough to survive the mission. In this paper, we shall report the logic and the results of this verification campaign

S on 1 testing of AR and HR designs at 1064 nm

In this paper, we present test results and involved procedures of a comprehensive test campaign for S on 1 testing of laser optics with large test areas allowing the generation of a profound test database for further analysis. This database will serve as a starting point for an empirical study of the lifetime of laser optics, which will be discussed in companion paper somewhere in these proceedings [1]*. The optics are designed to operate as anti-reflective or high-reflective components at the respective test wavelengths for 0° angle-of-incidence. Both, coatings and substrates of 2.0 inch diameter are produced from the same batches to be as identical as possible. There were two different coating technologies used, e-beam and IAD e-beam, to explore a possible effect of the coating process on the long term laser irradiation behavior. The laser damage test bench is operated with a laser source delivering laser pulses in a single longitudinal mode at a repetition frequency of 100 Hz. The beam profile is of a Gaussian-shape and of high spatial quality at the fundamental Nd:YAG laser wavelength with a pulse duration of 3.5 ns at 1064 nm. Typical beam diameters on the samples were 400 μm, and usually more than 500 test sites are irradiated in one test to achieve statistical significance. The laser test procedure itself is adapted from the ISO standard 11254-2 for multiple pulse irradiations, and the LIDT evaluation is done accordingly

An empirical investigation of the laser survivability curve: VIII-summary

This paper summarizes our results of S-on-1 testing carried out over the last few years. Our experimental data sets were taken with nanosecond laser pulse durations. An attempt was made to use the same scaling laws with femtosecond pulse widths but it was not successful. The conclusion was made: there is no single model than can universally applied to all kinds of survivability curves. We present this summary with a particular goal of making recommendations to those involved in the periodic review of ISO 21254. A preliminary review of models, describing damage threshold Evolution with respect to incident laser pulses, is made

Qualification of laser optics for upcoming ESA space laser missions

As a consequence of the ongoing interest for deployment of laser systems into space, suitable optical components have to be developed and must be extensively space qualified to ensure reliable, continuous, and autonomous operation. The exposure to space environment can adversely affect the longevity of optics, mainly coatings, and lead to system degradation. An increased operational risk is due to the air-vacuum effect, which can strongly reduce the laser damage resistance of optical coatings. For this purpose, a vacuum laser damage test bench has been developed and is operated at the DLR laser labs. In extensive test campaigns, all damage-prone optics of the ALADIN laser system (being the laser source of the upcoming ESA ADM Aeolus mission) were tested under operative conditions at the fundamental and at the harmonic wavelengths of Nd:YAG. Related scientific as