Second-harmonic Frequency-resolved Optical Gating Research Articles

Nonlinear refractive index measurement by SPM-induced phase regression.

Herewith, we describe how intensity and phase of the ultrashort pulse retrieved with second-harmonic frequency-resolved optical gating (SHG FROG) can be utilized for measurement of the nonlinear refractive index (n2). Through comparison with available literature, we show that our method surpasses Z-scan in terms of precision by a factor of two, and thus, constitutes an interesting alternative. We present results for various materials: fused silica, calcite, YVO4, BiBO, CaF2, and YAG at 1030 nm. Unlike the Z-scan, the use of this method is not restricted to free-space geometry, but due to its characteristics, it can be used in integrated waveguides or photonic crystal fibers as well.

Second-harmonic frequency-resolved optical gating covering two and a half optical octaves using a single spectrometer

We report the measurement of laser pulse shapes covering the range 580–3250 nm using second-harmonic generation frequency-resolved optical gating equipped with a single inexpensive visible-NIR miniature spectrometer and a single pair of homemade broadband beam splitters. Our experimental scheme exploits frequency up-conversion by BBO crystals and appropriate corrections for dispersion, beam splitter filtering and phase-matching efficiency. The signal and idler waves from a commercial optical parametric amplifier pumped by a Ti:Sapphire laser (26 fs, 1 kHz) have been characterized as well as their second harmonic. The pulse shapes out of a commercial difference frequency generation module mixing signal and idler have also been measured up to 3250 nm. The resulting pulses range from 20 to 120 fs, and their chirp characteristics are also exposed. Our approach is demonstrated over most of the doubling crystal transparency range.

Background-free collinear autocorrelation and frequency-resolved optical gating using mode multiplexing and demultiplexing in aperiodically poled lithium niobate waveguides

We use mode multiplexing and demultiplexing in apodized aperiodically poled lithium niobate waveguides to enable characterization of picosecond optical pulses in a collinear but background-free way using autocorrelation and second-harmonic frequency-resolved optical gating.

Propagation of self-focusing laser pulses in atmosphere: experiment versus numerical simulation

Numerical simulations of self-focusing laser pulses obtained via a slowly evolving wave approach (modified nonlinear Schrodinger equation) are compared with published experimental results in fused silica as well as with experimental results in air and fused silica obtained in our laboratory. The mathematical model includes group-velocity dispersion and third-order dispersion, optical shock, and both instantaneous Kerr and delayed Raman nonlinearities as well as a perfectly matched layer absorbing boundary condition. Second-harmonic frequency-resolved optical gating data taken after 10.91 m of propagation allow a direct comparison between experimental and computational envelopes at a number of pulse energies. FWHM measurements of the spectral width, intensity autocorrelation duration, and pulse radius at distances of 4.35, 10.91, 17.47, and 22.73 m provide a view of model fidelity across both energy and propagation distance variables. The magnitude of the nonlinear refractive index, n2, is inferred.

Real time femtosecond optical pulse measurement using a video-rate frequency-resolved optical gating system

We describe an improved instrument for measuring at video rate (30 frames per second) the second-harmonic frequency-resolved optical gating trace of femtosecond pulses from a mode-locked laser oscillator. The system comprises separate scanning acquisition and pulse retrieval elements which together enable the exact pulse profile to be viewed in real time with a typical refresh rate of 1 Hz. Details are given of the optical system used, the electronic synchronization circuits and the acquisition and retrieval software employed.

Molecular engineering of polymer films for amplitude and phase measurements of Ti:sapphire femtosecond pulses

Using second-harmonic frequency-resolved optical gating and a tricyanovinylaniline polymer thin film, we have measured the amplitude and the phase of mode-locked Ti:sapphire laser pulses as short as 13 fs. These thin films are ideally suited for ultrashort-pulse diagnostics because they eliminate the angle tuning associated with birefringent phase-matched crystals, minimize pulse distortions introduced by group-velocity dispersion, and exhibit excellent photochemical stability.