It had been known that the near-infrared is the most transparent optical region. In early 2000' s, near infrared imaging device came into market for various imaging use as the fruit of fiber optics communication development. Various near-infrared laser diodes are also becoming convenient and inexpensive for easy operation and compact device designs. The author's group has developed both fluorescent nanomaterials and various photonic devices for biomedical applications. The transparency of matter is dominated by dielectric constant, in other words, electric dipole moments and their distribution. The responsibility to the constant can be controlled by selecting wavelength. The paper reviews the scientific background of transparency, as well as the developments including fluorescence imaging, photodynamic therapy, thermal imaging, hyperspectral imaging and their biomedical applications.
