Time-resolved optical gating based on dispersive propagation: a new method to characterize optical pulses

Abstract

Abstract-We introduce the technique of time-resolved optical gating (TROG) based on dispersive propagation (DP), a new noninterferometric method for characterizing ultrashort optical pulses in amplitude and phase without the need for a short optical gating pulse. TROG is similar to frequency-resolved optical gating except that the role of time and frequency is interchanged. For the DP-TROG geometry, we show that measurements of the autocorrelation trace of the pulse after propagation through a medium with variable dispersion together with a single measurement of its intensity spectrum contain sufficient information to reconstruct the pulse in amplitude and phase. Pulse reconstruction for this DP-TROG geometry works very well even for the case of a nonlinearly chirped double pulse. Compared with other methods, DP-TROG does not introduce an ambiguity in the direction of time for the pulse. Due to its simplicity and improved sensitivity, DP-TROG is expected to be useful in characterizing low-energy pulses.Index Terms-Optical correlators, optical fiber dispersion, optical propagation in dispersive media, optical pulse compression, optical pulse measurements, pulse characterization, time-domain measurements.

Pulse characterization at 1.5 μm using time-resolved optical gating based on dispersive propagation

“…Although this method offers a simple solution without an iterative algorithm, it requires external modulation and electrical synchronization of the pulse train which is not always available especially in the case of high pulse repetition rates. We recently introduced and theoretically investigated the technique of time resolved optical gating based on dispersive propagation (DP-TROG) to characterize optical pulses [2]. Although there are other techniques that employ dispersion and cross correlation with a short gate pulse to characterize a pulse [3], our technique measures the autocorrelation trace of the dispersed pulse and does, therefore, not require a short gate pulse.…”

“…In TROG the pulse properties are derived with a similar iterative algorithm as in FROG. For more details on the duality between TROG and FROG the reader is referred to [2]. Compared to FROG based on second harmonic generation (SHG), the DP-TROG technique does not have an ambiguity in the direction of time for the pulse and although DP-TROG is not a single-shot measurement, it has a power advantage over FROG as the SHG does not need to be spectrally resolved.…”

“…We now follow the pulse reconstruction procedure for the compressed pulse as described in [2]. We first calculate , the Fourier transform of with respect to .…”

“…In order to enhance the noise features in this trace we have plotted its square root. We next transform this trace into the DP-TROG trace [2] (4) by evaluating the trace at points . The trace with cannot be evaluated in this way but is constructed from the measured intensity spectrum of the pulse.…”

“…The trace with cannot be evaluated in this way but is constructed from the measured intensity spectrum of the pulse. In order to speed up and improve algorithm convergence we interpolate the resulting trace in the -direction as described in [2]. We next apply a noise reduction technique to the DP-TROG trace to limit the influence of additive noise on the pulse reconstruction.…”