Time-domain interferometry for direct electric field reconstruction of mid-infrared femtosecond pulses

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.

Forty-photon-per-pulse spectral phase retrieval by shaper-assisted modified interferometric field autocorrelation

We retrieve the spectral phase of 400 fs pulses at 1560 nm with 5.2 aJ coupled pulse energy (40 photons) by the modified interferometric field autocorrelation method, using a pulse shaper and a 5 cm long periodically poled lithium niobate waveguide. The carrier-envelope phase control of the shaper can reduce the fringe density of the interferometric trace and permits longer lock-in time constants, achieving a sensitivity of 2.7×10(-9) mW(2) (40 times better than the previous record for self-referenced nonlinear pulse measurement). The high stability of the pulse shaper allows for accurate and reproducible measurements of complicated spectral phases.

Cross-correlation frequency-resolved optical gating for mid-infrared femtosecond laser pulses by an AgGaGeS(4) crystal

We introduce an AgGaGeS(4) crystal for sum-frequency generation in cross-correlation frequency-resolved optical gating (XFROG) to characterize mid-IR femtosecond laser pulses between the wavelengths of 3 microm and 11 microm. The performance of the AgGaGeS(4) crystal was examined by comparing it with a LiNbO(3) crystal, which has been frequently used in the near- to mid-IR region. We can obtain XFROG images by the AgGaGeS(4) crystal with efficiency 30 times greater than LiNbO(3) at the wavelength of 5 microm.

Mid-infrared electric field characterization using a visible charge-coupled-device-based spectrometer

We characterize ultrashort mid-infrared pulses through upconversion by using the stretched pulses obtained from the uncompressed output of a chirped-pulse amplifier. The power spectrum thus translated into the visible region can be readily measured with a standard silicon CCD camera-based spectrometer. The spectral phase is also characterized by a variant of zero-added-phase spectral phase interferometry for direct electric field reconstruction. This is a general method that provides a multiplex advantage over conventional infrared detector array-based methods.