Vibration Property of a Cryogenic Optical Resonator within a Pulse-Tube Cryostat

Cryogenic ultrastable laser cavities push laser stability to new levels due to their lower thermal noise limitation. Vibrational noise is one of the major obstacles to achieve a thermal-noise-limited cryogenic ultrastable laser system. Here, we carefully analyze the vibrational noise contribution to the laser frequency. We measure the vibrational noise from the top of the pulse-tube cryocooler down to the experiment space. Major differences emerge between room and cryogenic temperature operation. We cooled a homemade 6 cm sapphire optical resonator down to 3.4 K. Locking a 1064 nm laser to the resonator, we measure a frequency stability of 1.3×10−15. The vibration sensitivities change at different excitation frequencies. The vibrational noise analysis of the laser system paves the way for in situ accurate evaluation of vibrational noise for cryogenic systems. This may help in cryostat design and cryogenic precision measurements.

Urban Noise Pollution Prevention — Tokyo Case Study

Nowadays most of the world’s metropolises, cities, and conglomerations are substantially contaminated by noise. Development of civilization based on the intensification of car, rail, and air traffic, an increase of building density and, consequently, green areas reduction has led to major problems. Highlighting this negative phenomenon was one of the main objectives of this article. The process of noise pollution reduction is hindered not only by the needs of population growth, but also in a number of selected cities of the United States, Europe or Asia — aggressive sounds together with light and visual communications — emitted into public space, become an important element of commercial activities and remain a permanent, and even desirable, element of community culture and entertainment. The outlined problems are referred to in the introduction and discussion parts of this manuscript. At the same time, there are a number of solutions, both those currently applied and those possible to be introduced into the space of cities, which allow reduction of noise in selected zones of public and private sectors. One of the examples in the discussed field of science and practice is Tokyo — a multi-million metropolis, in which residents can experience silence both in workplaces, on streets and at home, despite the extraordinary civilization development of this metropolitan structure. Outcome analysis of solutions, used in the example city, forms the second part of the discussion in the article. Nowadays, when cities of the world are polluted with unwanted sounds, this case study is valuable, allowing the formulation of a set of clear recommendations for noise limitation in urban spaces — which are presented in the conclusions of the article. It is also worth mentioning that the spread of smart and humanized solutions aimed at noise reduction is crucial in order to build user- and environment-friendly urban environments in the near future.