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Tumors contain cells that continue to divide beyond normal limits. This is in contrast to most somatic cells, which arrest their cell cycle or die after a finite number of cell divisions, a phenomenon described as senescence. Among the exceptions are certain stem cells that do not senesce throughout an individual's life span. Germline cells, however, have not aged during the existence of mankind. Cellular senescence is genetically dominantly controlled by senescence genes [Bringold and Serrano 2000; Campisi 1997, 2000], which act in part by inducing cell cycle arrest. Hence, many tumor suppressor genes also act as senescence genes. This has led to the hypothesis that cellular senescence evolved as a defense against cancer. Cells can respond to carcinogenic stimuli by entering a senescent state. Cellular senescence thereby consigns cells to mortality in order to protect them against transformation. [ABSTRACT FROM AUTHOR]

At present, optical measurement methods are the most powerful tools for basic and applied research and inspection of the characteristic properties of a variety of materials, especially following the development of lasers and computers. Optical measurement methods are widely used for optical spectroscopy including linear and nonlinear optics and magneto-optics, conventional and unconventional optical microscopy, fiber optics for passive and active devices, optical recording for CD/DVD and MO disks, and various kinds of optical sensing. In this chapter, as an introduction to the following sections, the concept and fundamentals of optical spectroscopy are described in Sect. 11.1, including optical measurement tools such as light sources, detectors and spectrometers, and standard optical measurement methods such as reflection, absorption, luminescence, scattering, etc. A short summary of laser instruments is also included. In Sect. 11.2 the micro-spectroscopic methods that have recently become quite useful for nano-science and nano-technology are described, including single-dot/molecule spectroscopy, near-field optical spectroscopy and cathodo-luminescence spectroscopy using scanning electron microscopes. In Sect. 11.3 magneto-optics such as Faraday rotation is introduced and the superlattice of semi-magnetic semiconductors is applied for the imaging measurement of magnetic flux patters of superconductors as an example of spintronics. Sect. 11.4 is devoted to fascinating subjects in laser spectroscopy, such as nonlinear spectroscopy, time-resolved spectroscopy and THz spectroscopy. In Sect. 11.5 fiber optics is summarized, including transmission properties, nonlinear optical properties, fiber gratings, photonic crystal fibers, etc. In Sect. 11.6 optical recording technology for high-density storage is described in detail, including the measurement methods for the characteristic properties of phase-change and magneto-optical materials. Finally, in Sect. 11.7 a variety of optical sensing methods are described, including the measurement of distance, displacement, three-dimensional shape, flow, temperature and, finally, the human body for bioscience and biotechnology. This chapter begins with a section on basic technology for optical measurements. Sections 11.2–11.4 deal with advanced technology for optical measurements. Finally Sections 11.5–11.7 discuss practical applications to photonic devices. [ABSTRACT FROM AUTHOR]