Highlights: - The book is about the interaction of ultra short laser pulse in 40ps range with dental hard tissue(Enamel, Dentin and Dentin-enamel junction)wavelength. - 2nd and 4th harmonic generation of Nd:YAG laser interaction with dental tissue was studied extensively. - Study of crater depth morphology using scanning electron-microscope. - Study of crater depth in florescence microscope in reflection mode . - Ablation depth was enhanced by using consecutive pulses leaving the crater diameter unchanged. - Crater diameter depends both on laser FWHM and on ablation threshold, a model has been developed.