Method of checking unevenness of light-transmitting substance, apparatus therefor, and method of sorting transparent substrates

An apparatus for inspecting an ununiformity of a transparent material by introducing a laser beam therein, comprising:

• illumination means for introducing the laser beam into said transparent material;
• and
• detection means for detecting light leaked from said transparent material;
• wherein said transparent material comprises at least one pair of total reflective surfaces arranged so as to face each other in such a manner that the laser beam propagates along said pair of total reflective surfaces with being repeatedly and totally reflected therebetween, at least one pair of turning surfaces arranged so as to face each other in such a manner that the laser beam is turned back when the laser beam is impinged thereagainst, and an introductory surface for introducing the laser beam into said transparent material disposed in a manner to be sandwiched therebetween by at least one of said total reflective surfaces and at least one of said turning surfaces;
• said total reflective surfaces, said turning surfaces and said introductory surface being mirror-polished, and wherein said illumination means is arranged in a manner that the laser beam is introduced through said introductory surface into said transparent material to fill and spread within said transparent material.

A method for selecting a transparent material comprising steps of:

• preparing a transparent substrate;
• said substrate comprising an introductory surface for introducing a laser beam therethrough, at least one pair of main surfaces relatively facing each other, and at least one pair of end surfaces relatively facing each other;
• the laser beam propagating along said pair of main surfaces with being repeatedly and totally reflected therebetween and turning back when the laser beam impinges against said end surface;
• said main surfaces, said end surfaces, and said introductory surface being mirror-polished;
• introducing the laser beam through said introductory surface into said transparent substrate;
• detecting light leaked from said main surfaces and/or said end surfaces to generate a detection signal;
• and
• comparing said signal with predetermined information for presence or absence, a kind, and a size of the ununiformity of a transparent substrate, thereby selecting said transparent substrate.