Laser scanning overlap

The effects of laser parameters such as laser power (fluence), number of laser pulses induced to the surface (scanning speed) and laser beam overlap on the smface structure and wettability were examined. The various fabricated substrates were analyzed in terms of their geometrical characteristics. After laser irradiation, certain samples were subjected to silani-zation in order to reduce their surface energy. These surfaces were also analyzed in terms of their geometrical characteristics in order to determine the influence of silanization. 

Second-order NLO processes, including SFG, are strictly forbidden in media with inversion symmetry under the electric dipole approximation and are allowed only at the interface between these media where the inversion symmetry is necessarily broken. In the IR-Visible SFG measurement, a visible laser beam (covis) and a tunable infrared laser beam (cOir) are overlapped at an interface and the SFG signal is measured by scanning cOir while keeping cOvis constant. The SFG intensity (Isfg) is enhanced when coir becomes equal to the vibration levels of the molecules at the interface. Thus, one can obtain surface-specific vibrational spectra at an interface... 

Both the modes of operation described in Sect. 5.2 may be used for the detection of chemicals in liquid solution. Because the analyte s absorption line width is very broad, overlapping several (or many) WGMs, no tuning of the microresonator, or locking of a WGM to the scanning laser is necessary. In fact, a broadband source such as a light-emitting diode (LED) may be used. 

Atomic force microscopy (AFM) has become a standard technique to image with high resolution the topography of surfaces. It enables one to see nanoscopic surface features while the electrode is under potential control. This powerful probe microscopy operates by measuring the force between the probe and the samples (56,57). The probe consists of a sharp tip (made of silicon or silicon nitride) attached to a force-sensitive cantilever. The tip scans across the surface (by a piezoelectric scanner), and the cantilever deflects in response to force interactions between the tip and the substrate. Such deflection is monitored by bouncing a laser beam off it onto a photodetector. The measured force is attributed to repulsion generated by the overlap of the electron cloud at the probe tip with the electron cloud of surface atoms. 

If we have a two-level sample we expect to see a series of resonances separated by half the inverse of the repetition rate of the laser as the carrier frequency is scanned. If a second transition is within the bandwidth of the laser then this too will give rise to a series of resonances. The resulting spectrum is rather like that obtained from a Fabry-Perot interferometer with overlapping orders. However, in the mode-locked case the modes are precisely equally spaced in frequency. 

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