Astrophysics and Space Science

, Volume 35, Issue 2, pp 363–388 | Cite as

Parametric conversion and amplification of light in moving media

  • I. Lerche


We present calculations which should be of interest in connection with the problem of radiative transport through the magnetospheres of pulsars and the envelopes of quasars, where not only are particle speeds of the order of the speed of light expected, but also variations of refractive index with frequency and position.

The calculations show that by shining monochromatic light normally onto an interface between two media of different refractive indices it is relatively easy for the transmitted radiation to be spread out in frequency and of higher total intensity than the incident radiation. In asserting this we are assuming that the boundary between the two media is moving non-uniformly in time.

The two idealized examples which have been worked through to illustrate this parametric conversion and amplification mechanism are:
  1. (i)

    monochromatic light passing normally through a slab of material which is bounded by two fixed transparent plates and which is accelerating parallel to the plates. The intensity of the transmitted light exceeds the intensity of the incident light by a factorO(γ) where γ is the usual Lorentz factor.

  2. (ii)

    monochromatic light, of frequency ω, passing normally through a plane interface between vacuum and a medium of constant refractive index,n1, where the interface is oscillating around some fixed equilibrium position with a maximum speedO(c). In this case the transmitted intensity exceeds that which would be transmitted through an identical interface at rest by a factor 1+(γmax−1)(n1−1)2. For fixed refractive index and large γ this factor can be considerably in excess of unity. The frequency distribution of the transmitted radiation varies as ω−2/3 for frequencies in the range ϖ≪ϖ≪γ3ϖ.


Altogether, the calculations reported in this paper indicate that the production of broad-band, high-intensity radiation from relatively weak monochromatic light is a process which is likely to occur in most astrophysical objects where it is believed, or suspected, that rapid motions and spatial variations occur.


Refractive Index Incident Radiation Plane Interface Transmitted Intensity Rapid Motion 
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Copyright information

© D. Reidel Publishing Company 1975

Authors and Affiliations

  • I. Lerche
    • 1
  1. 1.Enrico Fermi InstituteUniversity of ChicagoChicagoUSA

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