Image Number 3 for United States Patent #6297894.
This invention discloses optical system and method for writing a refractive index pattern in a light transmissive or light absorbing sample. A light source for providing a short pulse laser beam in the femtosecond range having a low power per unit area is coupled to provide the short pulse beam to a diffractive optical element. A curved mirror collects light transmitted through or reflected from the diffractive optical element preserves an image relating to characteristics of the diffractive optical element encoded within the collected light, and directs the collected light in wavelength independent manner while preserving the image of the diffractive optical element encoded within the collected light. A rod lens demagnifies the image within the light received from the curved mirror so as to increase its power per unit area when directed to the light transmissive or absorbing sample to be permanently impressed therein.