  With electron beam durations down to femtoseconds and sub-femtoseconds
achievable in current state-of-the-art accelerators, longitudinal bunch length
diagnostics with resolution at the attosecond level are required. In this
paper, we present such a novel measurement device which combines a high power
laser modulator with an RF deflecting cavity in the orthogonal direction. While
the laser applies a strong correlated angular modulation to a beam, the RF
deflector ensures the full resolution of this streaking effect across the bunch
hence recovering the temporal beam profile with sub-femtosecond resolution.
Preliminary measurements to test the key components of this concept were
carried out at the Accelerator Test Facility (ATF) at Brookhaven National
Laboratory recently, the results of which are presented and discussed here.
Moreover, a possible application of the technique for novel accelerator schemes
is examined based on simulations with the particle-tracking code elegant and
our beam profile reconstruction tool.
