12/16/2023 0 Comments Light intensity equation![]() Accordingly the total flux over the shaded zone of the unit sphere = I × area of zone = I × 2 πr (cos θ) r δθ = I × 2 πr (cos θ) δθ since r = 1 in this case ( Fig. ![]() If I is the luminous intensity of L in some direction making an angle θ with the horizontal (0°–0° line) we may, without great error, suppose that over a small variation δθ of θ the intensity remains at this value I. If we imagine a sphere of unit radius, centre L, then we may compute the total flux crossing the surface of this sphere, and this is the total flux output from the source. Let us suppose that the same curve is obtained for any vertical plane through the centre of the source L-which is very nearly the case in practice for such a lamp. Luminous intensity measurements at various angles may be made using a Lummer–Brodhun photometer, for example, by turning the lamp L into various positions so that it makes different angles with the photometer bench. Thus LP is proportional to the luminous intensity of L as measured in the direction which makes an angle of 30° with the horizontal. This curve is plotted by drawing radial lines from a point representing the position of L, the lengths of these lines being proportional to the luminous intensity of L in the various directions. In this study, the polymer was excited by 730 nm laser light by the flying-spot technology within the bulk of the photoresists.įigure 25.12 represents a polar curve of luminous intensity such as might be obtained for a common filament lamp L. In conventional lithography SU-8 is illuminated with 365 nm light of a mercury lamp or by UV lasers. The epoxy based photoresist SU8 absorbs mainly below 400 nm. Non-destructive two-photon induced photochemical reactions such as photopolymerization occur when working at lower GW/cm 2 laser intensities and pJ laser pulse energies, respectively. For some materials, femtosecond laser pulses at light intensities of about 0.1 TW/cm 2 are sufficient to induce destructive low-density plasma effects. The onset of optical optical breakdown depends on the material. Inverse Bremsstrahlung and collision processes are not dominant. The primary cause for optical breakdown in the case of femtosecond pulses in transparent material is efficient multiphoton absorption. In water, the threshold for 100 fs pulses was found to be 2 orders lower than for 6 ns pulses. The threshold for optical breakdown decreases with the pulse width. Light intensities in the TW/cm 2 range can cause optical breakdown phenomena resulting in plasma formation and destructive thermomechanical effects. LeHarzic, in Handai Nanophotonics, 2007 2.2 Principle of multiphoton nanoprocessing
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