Three-halves harmonic emission from two-color experiments

Three-halves harmonic emission from a plasma in which the peak plasma density is nc>n>nc/4 has been temporally and spectrally resolved. This is achieved by using 0.53 μm wavelength laser light to irradiate a plasma preformed by 0.35 μm wavelength laser light. It is observed that both the backscattered red-shifted and blue-shifted peaks of the 3ω0/2 emission from the 0.53 μm laser disappear at approximately the same time. This result constrains the possible production mechanism for backscattered blue-shifted photons to scattering of the blue-shifted photons or plasmons close to nc/4.