Actually I m in complete agreement with you about the picture caption sorry I wasn t more clear I know that in dye lasers it s 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 I ll look into this more Thanks for your explanation of spectralon as that makes a great deal of sense Yes it would ve 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 I ve found on lasers Principles of Lasers by Oratio Svelto although the book is a little difficult to follow as 80 of it is written in math Anyhow thanks again for all of your assistance D