Actually Im in complete agreement with you about the picture caption sorry I wasnt more clear  I know that in dye lasers its often common to have a filter tube around the lamp usually just for water flow to absorb the NIR before it causes thermal shock in the liquid Ill look into this more  Thanks for your explanation of spectralon as that makes a great deal of sense Yes it wouldve been helpful if the article had not been deleted It is often helpful to include a small parenthetical explanation of specialized words anyway I can see where using a polished and AR coated rod would be beneficial in such a cavity coupling more light than difussing it through the surface of the rod I know from sad experience that keeping the light diffused either way is almost a necessity to keep the rod from cracking  I believe I also read that on the Kentek website and in one of the most accurate sources Ive found on lasers Principles of Lasers by Oratio Svelto although the book is a little difficult to follow as  of it is written in math  Anyhow thanks again for all of your assistance D