Abstract
In this paper, we introduce a pulse characterization technique that is free of phase-matching constraints, exploiting transient absorption in solids as an ultrafast optical switch. Based on a pump-probe setup, this technique uses pump pulses of sufficient intensity to induce the switch, while the pulses to characterize are probing the transmissivity drop of the photoexcited material. This enables the characterization of low-intensity ultra-broadband pulses at the detection limit of the spectrometer and within the transparency range of the solid. For example, by using zinc selenide (ZnSe), pulses with wavelengths from 0.5 to 20 μm can be characterized, denoting five octaves of spectral range. Using ptychography, we retrieve the temporal profiles of both the probe pulse and the switch. To demonstrate this approach, we measure ultrashort pulses from a titanium-sapphire (Ti-Sa) amplifier, which are compressed using a hollow core fiber setup, as well as infrared to mid-infrared pulses generated from an optical parametric amplifier (OPA). The characterized pulses are centered at wavelengths of 0.77, 1.53, 1.75, 4, and 10 μm, down to sub-two optical cycles duration, exceeding an octave of bandwidth, and with energy as low as a few nanojoules.
Highlights
With the advance of ultrafast laser technologies and nonlinear optics, ultrashort pulses from the UV to the mid-infrared are widely available [1,2,3,4]
This is the principle of frequency resolved optical gating (FROG) where an optical gate is created via a copy of the pulse [10], and of cross-correlation FROG where the gate is a second pulse [11]
80% of the pump energy is absorbed in the first 0.1, 18, and 0.3 μm at the surfaces of zinc selenide (ZnSe), Si, and Ge respectively. This precaution avoids the contribution of both group velocity mismatch and group delay dispersion due to propagation in the solid
Summary
With the advance of ultrafast laser technologies and nonlinear optics, ultrashort pulses from the UV to the mid-infrared are widely available [1,2,3,4]. Pulses over a broad spectral range are often simultaneously combined in pump-probe experiments. The characterization of such a variety of pulses requires different metrology techniques, depending on their specifications (i.e. energy, central wavelength, bandwidth). Other techniques use frequency conversion in order to couple the amplitude and phase of different frequencies contained in the optical pulses. This is the principle of frequency resolved optical gating (FROG) where an optical gate is created via a copy of the pulse [10], and of cross-correlation FROG (or X-FROG) where the gate is a second pulse [11]. As a summary of more than two decades of intense research activities on pulse characterization, we suggest the following literature for review on this topic: [11, 12]
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