Two-dimensional Spectral Shearing Interferometry Research Articles

Direct electric-field reconstruction of few-cycle mid-infrared pulses in the nanojoule energy range.

Amid the increasing potential of ultrafast mid-infrared (mid-IR) laser sources based on transition metal doped chalcogenides such as Cr:ZnS, Cr:ZnSe, and Fe:ZnSe lasers, there is a need for direct and sensitive characterization of mid-IR mode-locked laser pulses that work in the nanojoule energy range. We developed a two-dimensional spectral shearing interferometry (2DSI) setup to successfully demonstrate the direct electric-field reconstruction of Cr:ZnS mode-locked laser pulses with a central wavelength of 2.3 µm, temporal duration of 30.3 fs, and energies of 3 nJ. The reconstructed electric field is in reasonable agreement with an independently measured intensity autocorrelation trace, and the quantitative reliability of the 2DSI measurement is verified from a material dispersion evaluation. The presented implementation of 2DSI, including a choice of nonlinear crystal as well as the use of high-throughput dispersive elements and a high signal-to-noise ratio near-IR spectrometer, would benefit future development of ultrafast mid-IR lasers and their applications.

Coherent artifact study of two-dimensional spectral shearing interferometry

We study multi-shot intensity-and-phase measurements of unstable trains of ultrashort pulses using two-dimensional spectral shearing interferometry (2DSI). We find that, like other interferometric ultrashort-laser pulse-measurement methods, it measures only the coherent artifact and so yields effectively only a lower bound to the pulse length. We also attempt to identify warning signs of pulse-shape instability in 2DSI and find that it responds to instability with reduced fringe visibility, although this effect is very small when using the small spectral shears appropriate for large temporal ranges. We conclude that 2DSI should be used with caution and large-shear measurements or alternative techniques should be used to verify the stability of the pulse train.

Optimized ancillae generation for ultra-broadband two-dimensional spectral-shearing interferometry

We introduce a scheme to overcome the challenges of ancillae preparation in traditional spectrally-sheared interferometry techniques for pulse characterization. The approach, applied to two-dimensional spectral shearing interferometry, reliably characterizes few-optical-cycle pulses from UV to IR.

Microjoule-level, tunable sub-10 fs UV pulses by broadband sum-frequency generation.

We introduce a scheme for the generation of tunable few-optical-cycle UV pulses based on sum-frequency generation between a broadband visible pulse and a narrowband pulse ranging from the visible to the near-IR. This configuration generates broadband UV pulses tunable from 0.3 to 0.4 μm, with energy up to 1.5 μJ. By exploiting nonlinear phase transfer, transform-limited pulse durations are achieved. Full characterization of the UV pulse spectral phase is obtained by two-dimensional spectral shearing interferometry, which is here extended to the UV spectral range. We demonstrate clean 8.4 fs UV pulses.

Pulse synthesis in the single-cycle regime from independent mode-locked lasers using attosecond-precision feedback

We report the synthesis of a nearly single-cycle (3.7 fs), ultrafast optical pulse train at 78 MHz from the coherent combination of a passively mode-locked Ti:sapphire laser (6 fs pulses) and a fiber supercontinuum (1-1.4 μm, with 8 fs pulses). The coherent combination is achieved via orthogonal, attosecond-precision synchronization of both pulse envelope timing and carrier envelope phase using balanced optical cross-correlation and balanced homodyne detection, respectively. The resulting pulse envelope, which is only 1.1 optical cycles in duration, is retrieved with two-dimensional spectral shearing interferometry (2DSI). To our knowledge, this work represents the first stable synthesis of few-cycle pulses from independent laser sources.

Spectral Phase Characterization of Two-Octave Bandwidth Pulses by Two-Dimensional Spectral Shearing Interferometry Based on Noncollinear Phase Matching With External Pulse Pair

Noncollinear phase matching with an external powerful reference pulse pair and an extremely broadband pulse to be measured in two-dimensional spectral shearing interferometry enabled us to characterize its spectral phase over the so-far broadest wavelength range from 328 to 1363 nm. The method has the additional advantage of the shorter measurement time (10 s) and higher sensitivity (at least 100 times) compared to conventional modified spectral-phase interferometry for direct electric-field reconstruction. This result exceeding two octaves suggests a possibility of the first generation of a single subcycle pulse in the ultraviolet to near-infrared region by the application to the feedback chirp compensation of the induced phase-modulated pulse with the use of a recently developed spatial light modulator with an over-two-octave bandwidth.

Theory and design of two-dimensional spectral shearing interferometry for few-cycle pulse measurement

We provide a detailed discussion of our recently developed pulse characterization technique for few-cycle pulses, called two-dimensional spectral shearing interferometry (2DSI). Based on spectral phase interferometry for direct electric-field reconstruction (SPIDER), 2DSI is relatively simple to implement, but requires no interferometer delay or scan calibration. We show simulations of 2DSI in the presence of noise and find that it retains the favorable noise performance of spectral shearing methods, performing identically to standard SPIDER for a given measurement time. The optimal choice of experimental parameters is discussed, with results applicable to any spectral shearing method. Experimental considerations when building and operating a 2DSI are provided, with results shown for a 4.9 fs pulse, verifying the accuracy and precision of the 2DSI.

Two-dimensional spectral shearing interferometry resolved in time for ultrashort optical pulse characterization

We present a new scheme for coherent measurement of ultrashort optical pulses that relies on spectral shearing interferometry combined with all-optical time gating. The spectral phase is encoded along a temporal coordinate resulting in a two-dimensional (2D) self-referenced and self-calibrating set of data. The method works without time delay between the two interfering signals. The pulse amplitude and phase are reconstructed with a high signal-to-noise ratio using a direct algorithm that applies a Fourier transform (FT) to the 2D recorded interference pattern. Characterization of low-energy, high-repetition-rate femtosecond pulses of various shapes and validation of a single-shot operation are reported.

Two-dimensional spectral shearing interferometry for few-cycle pulse characterization

We present a new method for measuring the spectral phase of ultrashort pulses that utilizes spectral shearing interferometry with zero delay. Unlike conventional spectral phase interferometry for direct electric-field reconstruction, which encodes phase as a sensitively calibrated fringe in the spectral domain, two-dimensional spectral shearing interferometry robustly encodes phase along a second dimension. This greatly reduces demands on the spectrometer and allows for complex phase spectra to be measured over extremely large bandwidths, potentially exceeding 1.5 octaves.