Laser range finder using a nonlinear crystal

In a laser range finder, an apparatus comprising:

• an infrared ray laser source for emitting a ray of infrared light along a first direction of an optical axis, the optical axis having opposing first and second directions;
• a beam expander having opposing first and second sides, and disposed along the optical axis to receive, at the first side, a beam of light travelling in the first direction along the optical axis and at least partially including the ray of infrared light emanating from the infrared ray laser source, the beam expander emitting, from the second side, an expanded beam of light in the first direction along the optical axis, the beam expander comprising a first lens disposed at the first side, and a second lens disposed at a second side, wherein the first and second lenses are disposed along the optical axis and oriented with respect to one another so as to expand the beam of light travelling successively through the first and second lenses;
• a first beam splitter, having opposing front and rear surfaces, the front surface being coated with a material that fully reflects infrared light and only partially reflects visible light, the rear surface not reflecting visible light, the first beam splitter being disposed along the optical axis to receive, at the front surface, the expanded beam of light travelling in the first direction, the first beam splitter being oriented at an angle with respect to the optical axis such that an infrared light beam contained within the expanded beam of light will be reflected toward a potential target;
• a retro-reflector disposed along the optical axis and oriented so as to receive a visible ray of light travelling in the first direction along the optical axis and partially passing successively through the front and rear surfaces of the first beam splitter, the retro-reflector then reflecting the visible ray of light back toward the rear surface of the first beam splitter in the second direction along the optical axis;
• a telescope disposed to receive the visible ray of light after the visible ray of light has successively been first reflected by the retro-reflector and then at least partially reflected by the first beam splitter;
• a second beam splitter having a front surface coated with a material that only partially reflects infrared light, the second beam splitter being disposed along the optical axis between the infrared ray laser source and the beam expander to receive a returning ray of infrared light travelling in the second direction along the optical axis, the second beam splitter being oriented at an angle with respect to the optical axis such that the second beam splitter will at least partially reflect the returning ray of infrared light toward a detector;
• and
• a nonlinear crystal disposed along the optical axis between the infrared ray laser source and the first beam splitter for intercepting the ray of infrared light travelling in the first direction, and converting a portion thereof into visible light also travelling in the first direction along the optical axis, whereby the expanded beam of light comprises both infrared and visible light by the time it reaches the first beam splitter.