Broadband anti-reflection coating for the meter class Dark Energy Spectroscopic Instrument lenses

The Dark Energy Spectroscopic Instrument (DESI), currently under construction, will be used to measure the expansion history of the Universe using the Baryon Acoustic Oscillation technique. The spectra of 35 million galaxies and quasars over 14000 sq deg will be measured during the life of the experiment. A new prime focus corrector for the KPNO Mayall telescope will deliver light to 5000 fiber optic positioners. The fibers, in turn, feed ten broad-band spectrographs. We will describe the broadband AR coating (360 nm to 980nm) that was applied to the lenses of the camera system for DESI using ion assisted deposition techniques in a 3 m coating chamber. The camera has 6 lenses ranging in diameter from 0.8 m to 1.14 m, weighing from 84 kg to 237 kg and made from fused silica or BK7. The size and shape of the surfaces provided challenges in design, uniformity control, handling, tooling and process control. Single surface average transmission and minimum transmission met requirements. The varied optical surfaces and angle of incidence considerations meant the uniformity of the coating was of prime concern. The surface radius of curvature (ROC) for the 12 surfaces ranged from nearly flat to a ROC of 611 mm and a sag of 140 mm. One lens surface has an angle of incidence variation from normal incidence to 40°. Creating a design with a larger than required bandwidth to compensate for the non-uniformity and angle variation created the ability to reduce the required coating uniformity across the lens and a single design to be used for all common substrate surfaces. While a perfectly uniform coating is often the goal it is usually not practicable or cost effective for highly curved surfaces. The coating chamber geometry allowed multiple radial positions of the deposition sources as well as substrate height variability. Using these two variables we were able to avoid using any masking to achieve the uniformity required to meet radial and angle performance goals. Very broadband AR coatings usually have several very thin and optically important layers. The DESI coating design has layers approaching 3 nm in thickness. Having sensitive thin layers in the design meant controlling layer thickness and azimuthal variation were critical to manufacturing repeatability. Through use of strategically placed quartz crystal monitors combined with stable deposition plumes, the manufacturing variability was reduced to acceptable levels. Low deposition rates and higher rotation rates also provided some stability to azimuthal variation

Rights of Pachamama: The emergence of an earth jurisprudence in the Americas

Earth jurisprudence represents an alternative approach to the law based on the belief that nature has rights. In this view, a river has the right to flow, species have the right to continue to exist in the wild, and ecosystems have the right to adapt and evolve over time. Proponents of Earth jurisprudence argue that, by treating nature as exploitable resources, contemporary legal systems actively promote environmental harms. Recognising rights of nature, they argue, will transform core values and inspire social changes that promote economic development which respects nature’s limits. Since 2006, rights of nature have been recognised by some sub-federal public bodies in the United States and by the governments of Ecuador and Bolivia. This paper sets out to answer two questions. First, what explains the legal recognition of rights of nature in Ecuador and Bolivia? Second, what factors impede a wider adoption and implementation of Earth jurisprudence? Amongst the constraints, it will be argued, is that Ecuador and Bolivia continue to pursue an extractivist economic development model, with assertions of national sovereignty over natural resources tending to prevail over Earth jurisprudence and environmental conservation