March 8, 1922–December 8, 2002
BY JOSEPH L. BIRMAN AND HERMAN Z. CUMMINS
MELVIN (MEL) LAX WAS A versatile and productive theoretical physicist who made major contributions in many areas of science, including acoustics, multiple scattering of waves, disordered media, coherence and fluctuations in classical and quantum systems, applications of group theory to solids, phonon production and optics, and high-power lasers. His classic 1951 Reviews of Modern Physics paper on multiple scattering theory has been used in many areas of physics. For example, it led to the coherent potential approximation for disordered systems. His 1958 analysis with J. C. Phillips of electron motion in disordered systems showed how impurities randomly placed in a semiconductor crystal, or with random variation of interaction strength, will affect the energy levels and hence the conduction properties of the medium. This analysis was crucial for the early understanding of impurity bands in semiconductors, a topic of central importance in semiconductor device applications.
Mel wrote another influential Reviews of Modern Physics paper on “Fluctuations from the Nonequilibrium Steady State” in 1960. The laser was first demonstrated that same year, leading Mel to study fluctuation phenomena in lasers. During the 1960s he wrote a series of papers on classical and quantum noise. Almost all of these pertain to fluctuation