Optical Feedback

Flashback to the ’60s

I read Bill Silfvast’s interesting account about the early days of the He-Cd laser in the May 2014 issue of Optics & Photonics News. The early ’60s were exciting times, when visible CW gas lasers began to appear. As Bill has no doubt found, it is almost impossible today to convey the sense of wonder and excitement in the science community at that time because visible laser diodes are now so commonplace. The maser and infrared lasers never seemed to have the same impact emotionally on scientists and laymen, but the colored beams were different. They were something quite special! Even the hard-to-impress Bell Telephone Laboratories people were excited to see the colorful lasers beamed down the hallway. Everyone seemed anxious to probe the output beam with their fingers—to feel what they could see, I suppose.

Thank you very much for recalling those exciting days for all of us.

Alan White
Berkeley Heights, N.J., U.S.A.

Did You Find It?

I enjoyed Stephen Wilk’s Light Touch article, “The Mystery of Cryolite,” in the May 2014 issue of Optics & Photonics News. But he left us hanging! Did Wilk finally find transparent cryolite suitable for his optics demonstrations?

Gary Noyes
Encinitas, Calif., U.S.A.

THE AUTHOR RESPONDS: No, I did not find a sample of transparent cryolite—nor of cryolitholite, a related mineral with almost the same refractive index—for my demonstrations. I could have spent a lot of money for material with a thin coating of cryolite, but it was really out of my price range. I even wrote to some industrial cryolite suppliers, but I didn’t get a single response.

During my research, I found an interesting paper that described how to hydrothermally grow cryolite crystals. It occurred to me that if I got a sample of industrial cryolite, I might be able to get some of my colleagues who are familiar with growing crystals to produce a sample for me. Unfortunately, I have not pursued this any further.

Thank you for your letter.

Stephen R. Wilk
Saugus, Mass., U.S.A.

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