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Peter Sorokin (left) and Mirek Stevenson (right) adjusting the uranium calcium fluoride laser at IBM.
Peter P. Sorokin worked on some of the first lasers in the early 1960s. More recently, he’s been studying a long-standing astronomical mystery that may also involve coherent light.
Sorokin has been eyeing the so-called diffuse interstellar bands (DIBs), a series of broad absorption features in the spectra of stars within our galaxy. First noticed in the 1920s, astronomers have yet to come up with a definitive explanation of the phenomenon, though many say that complex interstellar organic molecules, such as polycyclic aromatic hydrocarbons (PAHs), create these bands when starlight undergoes linear scattering or linear absorption.
With a background in nonlinear optics from a career at IBM’s Thomas J. Watson Research Laboratories, Sorokin and his colleague James Glownia (now at Los Alamos National Laboratory) have been studying OB stars, which are the largest and hottest stars on the main sequence of stellar evolution. Such stars have a surface temperature of at least 20,000 K, compared with 6,000 K for the sun.
At September’s Frontiers in Optics conference in San Jose, Calif., Sorokin and Glownia presented their study of the 2175-Å extinction band as a postdeadline paper (PDP-B4). This DIB in the spectrum of hot main-sequence stars was first noticed 42 years ago. “It’s a true mystery in astronomy,” Sorokin said.
According to Sorokin, stimulated Rayleigh scattering, occurring in molecular hydrogen clouds that may surround these hot stars, would generate coherent light. The H2 clouds then absorb some of that light via the nonlinear process of two-photon absorption.
After looking at the ultraviolet spectra of 215 OB stars, the duo found a correlation between the strength of the 2175-Å band in a given star and the extent to which the molecular hydrogen is nonlinearly photoexcited via stimulated Rayleigh scattering.
Sorokin, a fellow of both IBM and OSA, won the Society’s 1978 R.W. Wood Prize for an outstanding discovery or invention in optics. He and Mirek Stevenson developed the second-ever working laser (uranium-doped calcium fluoride) in 1960, just months after Theodore Maiman’s ruby laser. Sorokin also co-discovered laser action in organic dyes in 1966 and pioneered the laser-pumped dye laser in 1969.
Sorokin and Glownia published a detailed exposition of their DIBs theory in 1996 (Astrophys. J. 473, 900). In a related news article in Science, however, some astronomers questioned whether the illuminating stars would produce enough intense coherent light to stimulate the two-photon absorption process. Sorokin and Glownia countered that the PAH hypothesis would require the even distribution of hundreds of types of carbon molecules through the galaxy.
Several noted journals have rejected the pair’s most recent papers, Sorokin told the FiO postdeadline gathering. He added: “It’s obvious they don’t understand nonlinear optics.”