Laser incubation effect

The investigation of incubation effects, i.e., that the optical, chemical, and mechanical properties of a (transparent) material can be changed during repetitive illumination of the same spot without ablation, is rather difficult because of the complicated surface structure of a biological composite material. It can be stated that one femtosecond laser pulse at F0=2.0 J cm-2 (roughly three times Fth) applied to healthy human enamel led to minor ablation (Fig. 32a). Five pulses of the same fluence resulted in a crater with a depth of 2-3 pm (Fig. 32b). The shape of the excision is well defined, and no cracks could be observed. 

Near-IR solid-state lasers (e.g., Ti sapphire) with chirped pulse amplification produce laser light with high brightness and very short pulses around 800 nm [ 116]. 150 fs laser pulse experiments on PI, polycarbonates (PC), PET, and PMMA have shown an increase in the single pulse ablation threshold from 1 J/cm for PI to 2.6 J/cm for PMMA. This corresponds well with the optical bandgaps of these polymers and indicates a multiphoton process. Incubation effects were observed for all polymers, but are more pronounced for PMMA, PC, and PET than for PI and PTFE, which are more stable [117-120]. Clear signs of molt redeposition of material can be observed for all polymers, except PI, which is not surprising, as it decomposes and does not melt. 

A sharp rise in the etch rate at the threshold is found only at the lowest laser wavelength (193 nm). At higher wavelengths, the curves bend smoothly upwards in an exponential fashion, indicating that there is also ablation below the threshold fluence point obtained by extrapolating the hnear portion of the curve to zero ablation rate. This was corroborated by a study on poly(methyl methacrylate) concerning the so-called incubation effect [52]. The latter refers to the phenomenon of the polymer surface being etched less deeply by the initially applied pulses than by subsequent pulses of the same fluence. Actually, material... 

Gomez, D. and Goenaga, 1. (2006) On the incubation effect on two thermoplastics when irradiated with ultrashort laser... 

The principle of direct immunoassays is that Abs are first tagged with FL labels and then mixed with the Ag sample of interest. The Ab should be in excess. After incubation, the mixture is injected into the capillary, and the amount of Ag can be determined by the Ab-Ag complex signal. Competitive immunoassays are usually preferred for small Ags because the separation of the Ab-Ag complex from the Ab can be very difficult for small Ags. As above, Shimura and Karger reported a direct immunoassay of hGH (61). Due to the focusing effect of CIEF (Fig. 4) and the high sensitivity of CE-laser-induced fluorescence (LIF), a detection limit of 0.1 ng/ml was achieved. Similarly, Chen demonstrated the direct immunoassay of IgG with a detection limit of 6 X1(T10 (74). 

---