In their extensive evaluation of Maxwell's equations at the planar interface between a linear and nonlinear medium, several rules for the interaction of light in non-linear mediums were elucidated.īefore the development of the first laser, Peter Franken made a $10 USD bet with his friend and colleague, Willis Lamb, that second-harmonic generation was possible. The formulation of SHG was initially described by N. Famously, when published in the journal Physical Review Letters, the copy editor mistook the dim spot (at 347 nm) on the photographic paper as a speck of dirt and removed it from the publication. They sent the output light through a spectrometer, recording the spectrum on photographic paper, which indicated the production of light at 347 nm. They focused a ruby laser with a wavelength of 694 nm into a quartz sample. The demonstration was made possible by the invention of the laser, which created the required high intensity coherent light. Weinreich at the University of Michigan, Ann Arbor, in 1961. Second-harmonic generation was first demonstrated by Peter Franken, A.
It is a special case of frequency multiplication. Generating the second harmonic, often called frequency doubling, is also a process in radio communication it was developed early in the 20th century, and has been used with frequencies in the megahertz range. In other cases, like second-harmonic imaging microscopy, only a tiny fraction of the light energy is converted to the second harmonic-but this light can nevertheless be detected with the help of optical filters.
These cases typically involve intense pulsed laser beams passing through large crystals, and careful alignment to obtain phase matching. In some cases, almost 100% of the light energy can be converted to the second harmonic frequency. In addition, in non-centrosymmetric crystals belonging to crystallographic point group 432, the SHG is not possible and under Kleinman's conditions SHG in 422 and 622 point groups should vanish although some exceptions exist. However, effects such as the Bloch–Siegert shift (oscillation), found when two-level systems are driven at Rabi frequencies comparable to their transition frequencies, will give rise to second harmonic generation in centro-symmetric systems. Second-harmonic generation, like other even-order nonlinear optical phenomena, is not allowed in media with inversion symmetry (in the leading electric dipole contribution). The second-order nonlinear susceptibility of a medium characterizes its tendency to cause SHG. It is a special case of sum-frequency generation (2 photons), and more generally of harmonic generation. Second-harmonic generation ( SHG, also called frequency doubling) is a nonlinear optical process in which two photons with the same frequency interact with a nonlinear material, are "combined", and generate a new photon with twice the energy of the initial photons (equivalently, twice the frequency and half the wavelength), that conserves the coherence of the excitation.