Tuning in to dye laser origins

The historical feature article on “The Early Days of Precision Laser Spectroscopy” ( Physics Today, January 2007, page 49 ) misidentified the inventor of the tunable dye laser as Peter Sorokin.

B. B. McFarland and I, both then at Korad Corp, were the actual “inventors” who first demonstrated that device and published the findings. ¹ The experimental design with a diffraction grating as one of the resonator cavity mirrors, as discussed in the Physics Today article, was first described by us. Tunability was one original aspect of that discovery; another was the narrowband energy efficiency of the laser, funneling a large portion of the original broadband laser emission into the narrow band of a selected wavelength.

Sorokin himself, in a published interview, ² gave full credit to that paper and its authors, adding that he had “missed the boat completely, … just hadn’t thought of it,” and saying that “Soffer and McFarland’s result was a tremendous surprise.” The reason for his and everybody’s surprise was no doubt the conventional but mistaken belief that the xanthine dye system, and in particular rhodamine 6G, was primarily inhomogeneously spectrally broadened at the relevant time scales. I examined the literature that supposedly validated that belief and found it unconvincing. The same surprising homogeneity story that upset published notions also turned out to apply to the cyanine dye family and the xanthines embodied in plastic, ¹ despite their famously long fluorescent lifetimes in solid solution.

That was some 40 years ago. The lesson to be learned now is that we must read everything with considered skepticism.