Does the use of UV light beam lead to poorer contrast in optical microscopy of cells than the higher wavelengths visible light?
Contrast in optical microscopy typically depends on different substances having different absorption spectra. Practically everything absorbs UV light, so there tends to be less contrast in that range than in the visible spectrum where there is a bit more selectivity.  All of this changes when there are contrast-enhancing substances added.  For example, molecules that absorb in one wavelength and emit at a different wavelength via fluorescence, attached to antibodies that bind selectively to specific cell components, can provide very high contrast.  E.g., see [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2156041/].

An alternative optical microscopy technique is phase-contrast microscopy which does not use absorption at all.  Instead, it measures the effective optical path length through the sample, which depends on local refractive index of the sample.

Yet another alternative is x-ray fluorescence microscopy, which can identify specific elements in the composition of a sample.  See, for example,[https://www.americanlaboratory.com/913-Technical-Articles/18833-Three-Dimensional-Elemental-Imaging-Using-a-Confocal-X-Ray-Fluorescence-Microscope/].