Pulse-by-pulse optical observation of laser-irradiated thin glass substrate using oil-immersion microscopy

To study the formation mechanism of laser-induced periodic surface structures, we carried out a pulse-by-pulse optical observation of laser-induced surface morphological changes on thin glass substrates. We adopted oil-immersion microscopy, which has a higher spatial resolution than dry microscopy, and the laser was irradiated from the air side. A thin transparent substrate of coverslip was used as the sample. When a scratched coverslip was irradiated with focused subnanosecond laser pulses of 1.064 µm wavelength, periodic structures occasionally appeared in the flat region near the focus, with a period of about 0.55 μm.

Ground Photometric Measurements Inversion Methods for Space Object Characteristics Based on Nonlinear Filtering: A Short Review

: The ground space optical observation system considered as one of the main measurement methods to observe space object in Medium Earth Orbit (MEO), Highly Elliptical Orbit (HEO), and Geostationary Orbit (GEO) experiences difficulties in forming high-solution images for objects located in GEO that only appear as several light spots with limited pixels due to the impacts of observing distance, resolution ratio, and other atmospheric conditions. The light curve is the time duration of an object’s observed brightness. Through light curves, right ascension, and declination of space objects obtained from the ground-based optical observation system, the characteristic of space objects such as position, velocity, size, shape, and material can be inverted. This paper has analyzed the principles, applications, merits, and demerits of several non-linear filtering methods in detail. Besides, the scientific description of inversion for characteristics of a non-resolved space object from ground photometric measurements and the essence of the non-linear filtering inversion method have also been clarified. A selection principle of the non-linear filtering inversion method for different space object characteristics is then proposed, and the developing direction of such inversion methods is also described in the end.