Absorption bleachable

Metal-free, chloroaluminum phthalocyanine [14154-42-8] vanadyl phthalocyanine [13930-88-6], or magnesium phthalocyanines are sufficiently soluble in organic solvents and show enough bleachable absorption at 694.3 nm to serve as repeated Q-switching elements for mby lasers (qv) (180). Phthalocyanines have been used in other lasers as weU (181). 

Data is also shown for bovine rhodopsin, 63, for comparison. The hydroretinals 66-68 presumably assume 9-cis or 11 -cis like conformations when bound to opsin. Retinals 67 and 68 form non-bleachable pigments, i.e., no change in their A, occurs upon exposure to room light irradiation by UV light leads to decomposition products instead of separation of the chromophore from opsin. a In MeOH. In case of split chromophores the absorption maxima of the enal moieties are given. b Protonated Schiff base with n-butylamine in MeOH. ... 

It was found that the contrast ratio ( cEL/y) can be expressed by using two parameters and a. Parameter is given by lo to > where e is the molar absorption coefficient, is the quantun yield of the bleachable material, and lb to is the sensitivity of the photoresist. Parameter is given by WTb-1, which represents th6 transmittance ratio of the bleached layer to the unbleached one. Similar parameters have been reported by Diamand and Sheats. (7)... 

Leary and Giampaolo [70] found that unbleached softwood TMP behaved differently upon alkali treatment than peroxide-bleached TMP. Unbleached softwood TMP was bleached with peroxide (4% charge) to an ISO brightness of 78% however, alkali-darkened pulp could only be bleached to 68% with the same peroxide charge. Borohydride reduction of the pulp before the alkali treatment inhibited the darkening and almost fully restored its bleachability. The absorption maximum for alkali darkening of unbleached pulp appeared at 420 nm, but was shifted to 360 nm if the pulp was pretreated with borohydride. 

Peroxide-bleached TMP regained all the brightness lost on alkali darkening upon subsequent peroxide bleaching. Borohydride pretreatment inhibited the alkali darkening, but was not required to maintain full bleachability of the pulp, except at 120°C. The maximum in the absorption difference spectrum was at 360 nm. 

For operation at 1550 nm, the efficiency is still severely reduced by absorption at the second-harmonic wavelength, which can be seen by comparing the theoretical performance including absorption (curve) and excluding absorption (open circle). Since DANS is a bleachable chromophore, waveguide damage is to be expected at higher SHG intensities, which was in fact observed [26]. 

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