468 Diagnostic Techniques
thickness, Rayleigh range ρ
0
of the focused fundamental beams, or the overlap-
ping region of the fundamental pulses in a noncollinear geometry. The shorter
the crystal, the broader the bandwidth over which phase matched harmonic
conversion is obtained, but the lower the conversion efficiency. There is clearly a
compromise to be reached between bandwidth and sensitivity. In Eq. (9.21), the
bandwidth efficiency factor η() includes only the frequency dependence of the
phase matching condition, and not a finite response time for the harmonic gener-
ation process. It is assumed here that the response time of the second harmonic
process is much shorter than the pulses to be measured, which is a reasonable
assumption since the second-order ...