| Optical Autocorrelation |
Article Index for Optical |
Website Links For Optical |
Information AboutOptical Autocorrelation |
| CATEGORIES ABOUT OPTICAL AUTOCORRELATION | |
| optical metrology | |
| lasers | |
| nonlinear optics | |
|
In the following examples, the autocorrelation signal is generated by second-harmonic generation (SHG), the lowest order (and hence the strongest) of all nonlinear optical processes. Higher-order nonlinear optical processes such as third-harmonic generation can also be used in autocorrelation measurements, in which case the mathematical expressions of the signal will be slightly modified, but the basic interpretation of an autocorrelation trace remains the same. Field autocorrelation detector.]] For a complex electric field , the field autocorrelation function is defined by
The Wiener-Khinchin theorem states that the Fourier transform of the field autocorrelation is the spectrum of , i.e., the square of the ''magnitude'' of the Fourier transform of . As a result, the field autocorrelation is not sensitive to the spectral ''phase''. The field autocorrelation is readily measured experimentally by placing a slow detector at the output of a Michelson Interferometer . The detector is illuminated by the input electric field coming from one arm, and by the delayed replica from the other arm. If the time response of the detector is much larger than the time duration of the signal , or if the recorded signal is integrated, the detector measures the intensity as the delay is scanned: | ||
| To A Complex Electric Field <math>E(t)</math> Corresponds An Intensity <math>I(t) | E(t)^2</math> and an intensity autocorrelation function defined by |
|
| : <math>I M( Au) | \int_{-\infty}^{+\infty}E(t)E(t- au)^2dt = \int_{-\infty}^{+\infty}I(t)I(t- au)dt</math> |
|
| : <math>I M( Au) | \int_{-\infty}^{+\infty}(E(t)+E(t- au))^2^2dt</math> |
|
|