Low-power optical examination

Optical Techniques. The most important tool in a museum laboratory is the low power stereomicroscope. This instmment, usually used at magnifications of 3—50 x, has enough depth of field to be useful for the study of surface phenomena on many types of objects without the need for removal and preparation of a sample. The information thus obtained can relate to toohnarks and manufacturing techniques, wear patterns, the stmcture of corrosion, artificial patination techniques, the stmcture of paint layers, or previous restorations. Any art object coming into a museum laboratory is examined by this microscope (see Microscopy Surface and interface analysis). 

Using an inverted microscope, equipped with phase contrast optics if possible, examine cell culture vessels individually. Scrutiny should be especially rigorous in cases in which large-scale production is involved. Check each culture first using low power. The suppliers listed provide the specific media required but other suitable vendors exist. Batches of media should be tested for optimal growth promotion before use in cell culture quality control. 

An examination of the optical activity, as a function of the viscometric molecular weight, has shown that the decrease in rotatory power at the end of the reaction is to be connected with the dilution of macromolecules having high molecular weight and relatively high optical activity, by macromolecules, which were formed later, having either low or no optical activity and low molecular weight (37). 

Zeiger has recently published a theoretical examination of the effect of traps on the SL linewidth. Given a sufficient density of trap states within the optical mode volume, a result similar to the observed behavior is obtained if the trap decay rates are at least of the order of the power-independent linewidth. The motivation for the trapping theory came in part from the widely observed l/f behavior in the low frequency current, amplitude and frequency noise spectra of SL s. This is discussed in more detail shortly. Similar behavior in the current fluctuation noise in semiconductors has been related to the presence of trap levels. 

Figure 7. Cross-sectional images of PA-6 joints examined (a) by optical microscope and (b) by SEM for low and high laser powers.

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