Method of making infrared crystalline fiber

A process for extruding an optical silver halide fiber, which comprises:

• providing a silver halide preform including top, bottom and lateral surfaces;
• placing said preform within a cylindrical extrusion chamber comprising an extrusion die;
• applying force to said preform while holding said preform in a fixed position wherein said silver halide flows through said extrusion die to produce a silver halide fiber wherein said force is provided by moving said extrusion die and a plunger within said cylindrical extrusion chamber in a direction opposite to said silver halide flow direction thereby reducing friction of said silver halide on said cylindrical chamber and reducing turbulence in said silver halide flow, said silver halide preform has a predetermined shape and cross section, and said plunger has a hollow portion having a cross section which is smaller than the cross section of said preform thus reducing contamination by impurities from lateral surfaces of said preform in the resulting silver halide fiber.