supercontinuum

thumb|Figure 1. A typical supercontinuum spectrum. The blue line shows the spectrum of the pump source launched into a photonic crystal fiber while the red line shows the resulting supercontinuum spectrum generated after propagating through the fiber. thumb|Image of a typical supercontinuum. This supercontinuum was generated by focusing 800 nm, sub-100 fs pulses into a yttrium aluminium garnet (YAG) crystal, generating ultra broadband light that spans both the visible and NIR. In optics, a supercontinuum is formed when a collection of nonlinear processes act together upon a pump beam in order to cause severe spectral broadening of the original pump beam, for example using a microstructured optical fiber. The result is a smooth spectral continuum (see figure 1 for a typical example). There is no consensus on how much broadening constitutes a supercontinuum; however researchers have published work claiming as little as 60 nm of broadening as a supercontinuum. There is also no agreement on the spectral flatness required to define the bandwidth of the source, with authors using anything from 5 dB to 40 dB or more. In addition the term supercontinuum itself did not gain widespread acceptance until this century, with many authors using alternative phrases to describe their continua during the 1970s, 1980s and 1990s.

thumb|Typical coloured pattern from a femtosecond beam tight focused in air; note the beam is passing from right, being invisible until a spark is generated due to strong electric field in its focus