  We demonstrate that full temporal characterisation of few-cycle
electromagnetic pulses, including retrieval of the carrier envelope phase
(CEP), can be directly obtained from Frequency Resolved Optical Gating (FROG)
techniques in which the interference between non-linear frequency mixing
processes is resolved. We derive a framework for this scheme, defined Real
Domain-FROG (ReD-FROG), as applied to the cases of interference between sum and
difference frequency components and between fundamental and sum/difference
frequency components. A successful numerical demonstration of ReD-FROG as
applied to the case of a self-referenced measurement is provided. A
proof-of-principle experiment is performed in which the CEP of a single-cycle
THz pulse is accurately obtained and demonstrates the possibility for THz
detection beyond the bandwidth limitations of electro-optic sampling.
