An empirical investigation of the laser survivability curve: V

In this paper, we report on a continuing multi-year empirical investigation into the nature of the laser survivability curve. The laser survivability curve is the onset threshold as a function of shot number. This empirical investigation is motivated by the desire to design a universal procedure for the measurement of the so-called S on 1 damage threshold. In this year’s paper we investigate the usefulness of scaling the fluence with shot number. First the scaling process is defined and applied to a result from our experimental archives. The probability of damage curve for a single shot test is extrapolated to 104 shots. The scaled result is shown to be very close the observed results providing a basis for extrapolation to very large values of n

Quantifying full phenological event distributions reveals simultaneous advances, temporal stability and delays in spring and autumn migration timing in long-distance migratory birds

Acknowledgements We thank all Fair Isle Bird Observatory staff and volunteers for help with data collection and acknowledge the foresight of George Waterston and Ken Williamson in instigating the observatory and census methodology. We thank all current and previous directors of Fair Isle Bird Observatory Trust for their contributions, particularly Dave Okill and Mike Wood for their stalwart support for the long-term data collection and for the current analyses. Dawn Balmer and Ian Newton provided helpful guidance on manuscript drafts. We thank Ally Phillimore and two anonymous referees for helpful comments. This study would have been impossible without the Fair Isle community's invaluable support and patience over many decades, which is very gratefully acknowledged. WTSM and JMR designed and undertook analyses, wrote the paper and contributed to data collection and compilation, MB contributed to analysis and editing, all other authors oversaw and undertook data collection and compilation and contributed to editing.Peer reviewedPostprin

Case Reports1. A Late Presentation of Loeys-Dietz Syndrome: Beware of TGFβ Receptor Mutations in Benign Joint Hypermobility

Background: Thoracic aortic aneurysms (TAA) and dissections are not uncommon causes of sudden death in young adults. Loeys-Dietz syndrome (LDS) is a rare, recently described, autosomal dominant, connective tissue disease characterized by aggressive arterial aneurysms, resulting from mutations in the transforming growth factor beta (TGFβ) receptor genes TGFBR1 and TGFBR2. Mean age at death is 26.1 years, most often due to aortic dissection. We report an unusually late presentation of LDS, diagnosed following elective surgery in a female with a long history of joint hypermobility. Methods: A 51-year-old Caucasian lady complained of chest pain and headache following a dural leak from spinal anaesthesia for an elective ankle arthroscopy. CT scan and echocardiography demonstrated a dilated aortic root and significant aortic regurgitation. MRA demonstrated aortic tortuosity, an infrarenal aortic aneurysm and aneurysms in the left renal and right internal mammary arteries. She underwent aortic root repair and aortic valve replacement. She had a background of long-standing joint pains secondary to hypermobility, easy bruising, unusual fracture susceptibility and mild bronchiectasis. She had one healthy child age 32, after which she suffered a uterine prolapse. Examination revealed mild Marfanoid features. Uvula, skin and ophthalmological examination was normal. Results: Fibrillin-1 testing for Marfan syndrome (MFS) was negative. Detection of a c.1270G > C (p.Gly424Arg) TGFBR2 mutation confirmed the diagnosis of LDS. Losartan was started for vascular protection. Conclusions: LDS is a severe inherited vasculopathy that usually presents in childhood. It is characterized by aortic root dilatation and ascending aneurysms. There is a higher risk of aortic dissection compared with MFS. Clinical features overlap with MFS and Ehlers Danlos syndrome Type IV, but differentiating dysmorphogenic features include ocular hypertelorism, bifid uvula and cleft palate. Echocardiography and MRA or CT scanning from head to pelvis is recommended to establish the extent of vascular involvement. Management involves early surgical intervention, including early valve-sparing aortic root replacement, genetic counselling and close monitoring in pregnancy. Despite being caused by loss of function mutations in either TGFβ receptor, paradoxical activation of TGFβ signalling is seen, suggesting that TGFβ antagonism may confer disease modifying effects similar to those observed in MFS. TGFβ antagonism can be achieved with angiotensin antagonists, such as Losartan, which is able to delay aortic aneurysm development in preclinical models and in patients with MFS. Our case emphasizes the importance of timely recognition of vasculopathy syndromes in patients with hypermobility and the need for early surgical intervention. It also highlights their heterogeneity and the potential for late presentation. Disclosures: The authors have declared no conflicts of interes

Laser qualification testing of space optics

Laser optics being used in space laser systems are usually exposed to high vacuum conditions under the absence of air or oxygen. In the past, several space-based laser missions have suffered from anomalous performance loss or even failure after short operation times. To mitigate the risks involved in these long-term operational conditions, a laser damage test bench has been developed and is operated at the German Aerospace Establishment to test laser optics in the IR, VIS, and in the UV spectral range. The testing is performed under application oriented conditions, i.e. under high-vacuum using dry pump systems. The main goal of the test campaign is to identify the critical components in terms of their laser damage threshold for very high pulse numbers applied per site. Characteristic damage curves according to ISO 11 254 are evaluated for each component under investigation for up to 10 000 shots per site. The characteristic damage curves are used for the estimation of the performance at very high pulse numbers. The typical behavior found was a sharp drop in LIDT for small pulse numbers followed by a smooth decrease for larger pulse numbers (laser fatigue effect)

Vacuum laser damage test bench

This work summarizes the results from an extensive test campaign in which space-based laser optics were qualified for the upcoming ESA ADM-Aeolus mission. 14 different types of optical components from different suppliers were tested at the Nd:YAG laser wavelength according to the ISO standard 11 254 – 2 for multiple pulse testing. A new technique based on transient pressure sensing was developed to monitor the occurrence of damage on a sample surface exposed to a vacuum environment. Parallel testing of reference samples showed a distinct degradation under vacuum compared to atmospheric or pressurized environment. For all samples tested we found a typical behavior in the characteristic damage curves attained: A sharp drop in LIDT for small pulse numbers followed by a smooth decrease for larger pulse numbers (laser fatigue effect)

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

Space-qualification testing of laser-optics

Laser optics operated under a high-vacuum environment are exposed to an increased risk of failure. The main adverse effects are laser-induced contamination and coating degradation. This paper addresses test procedures, results and lessons-learned from long-term test campaigns carried out at ESA/ESTEC and DLR