## Space Probe Conjugate

To determine the parameter B from Eq. (50), the voltage signal levels must be calibrated against the pulse energy measurements. Since the beams are centered on the camera slit, the streak camera integrates the beam over the slit width Δy. The recorded signal S(x’ t) is proportional to the beam intensity

S(x’ t) = bΔyI(x’ 0, t) (55)

where b is a constant and I(X’ y, t) — I(x, 0, t) over the narrow slit width. Assuming axial symmetry for the beam implies that

b = 2π εΔy

The integration can be performed numerically with

∞0 S(x, t)xdxdt

where (x0’ t0) are the pixels defining the origin. Now

With R(tmin) determined by Eq. (58), this quantity is then plotted as a function of pump energy. The data are then fitted to Eq. (50) to determine the parameter B. An example of these data for a solution of diphenyl butadiene in chloroform is given in Fig. 20 [5]. Similar procedures are used to find Bref for the reference measurement. Then Eqs. (53) and (54) may be used to find the imaginary part of the susceptibility and hence β.