Ultrasonics in the Tetrahertz Frequency Range-Theories.- Optical Transducers.- Theories and Experiments.- Quantum Theory of Terahertz Frequency Range.- Application to Nanoacoustical Imaging with Nanometer Image Resolution.- SASER-Theories and Principles based on Tetrahertz Ultrasound.- Transducers for SASER.- Applications of SASER.- Quantum Acoustical Imaging based on Quantum Mechanical Properties-Phonon Entanglement.- Quantum Acoustical Microscope based on Entanglement-Enhancement of Image Resolution.- Conclusions.