Sensitization of photo-thermo-refractive glass to visible radiation by two-step illumination

A method of generating optical components from photo-thermo-refractive (PTR) glasses, comprising the steps of:

• providing a PTR glass blank having a total contamination with iron and heavy metals of a few per million;
• exposing the entire PTR glass blank with a UV light having a wavelength within the limits of the UV spectrum to produce precursors of nucleation centers which are color centers;
• generating a high intensity visible light greater than approximately 10 MW/cm2;
• exposing the UV exposed PTR glass with the high-intensity visible light for optical excitation of the color centers to partially bleach the color centers to record a phase hologram by refractive index modulation, the partial bleaching being non linear due to the high-intensity visible light exposure;
• thermal treating the UV and visible light exposed PTR glass;
• and
• cooling the thermal treated PTR glass to generate a holographic optical component from the thermal treated PTR glass for a visible region.

An apparatus comprising:

• a photo sensitive refractive (PTR) glass;
• a UV source for exposing the PTR glass to produce a PTR glass having photosensitivity to visible light caused by the UV exposure to create precursors of nucleation centers which are color centers in the PTR glass, the PTR glass having a total contamination with iron and heavy metals of a few parts per million,
• a visible light source for exposing the UV exposed PTR glass which is operating to generate a high intensity visible light greater than approximately 10 MW/cm2 to decrease concentration of the precursors of nucleation center to decrease the rate of crystallization at the development stage to increase a refractive index in the PTR glass after exposure to the visible light for non linear transformation of the nucleation centers;
• a heating unit for thermal treating the UV and visible light treated PTR glass to provide phase transformation depending on an amount and intensity of visible radiation to allow crystal growth in the UV exposed area using a nonlinear mechanism for destruction of nucleation centers in an area exposed to visible light to fabricated a hologram or a phase plate from the PTR glass for a visible region, the hologram generated by refractive index modulator;
• and
• means for using the PTR glass as one of a refractive and a diffractive volume holographic optical element based on modulation of a refractive index.

A method of generating refractive optical elements from photo-thermo-refractive (PTR) glasses, comprising the steps of:

• providing a PTR glass having a total contamination with iron and heavy metals of a few parts per million;
• exposing PTR glass with a source of UV radiation for generation of precursors of nucleation centers which are color centers;
• generating a visible light having an intensity greater than 10 MW/cm2;
• exposing the UV exposed PTR glass with a high-intensity visible light source to decrease concentration of the precursors of nucleation centers to decrease the rate of crystallization at the development stage to increase a refractive index in the PTR glass after exposure to the visible light for a nonlinear transformation of nucleation centers;
• thermal treating the UV and visible light exposed PTR glass to provide phase transformation depending on an amount and intensity of visible light radiation to allow crystal growth in the UV exposed area using a nonlinear mechanism for destruction of nucleation centers in the area exposed to visible light, wherein after thermal treatment a refractive index in the UV and Visible light exposed area is higher than in a single exposed area and lower than in unexposed areas;
• and
• replaying a hologram from the exposed and thermal treated PTR glass.