Efficient broadband 400 nm noncollinear second-harmonic generation of chirped femtosecond laser pulses in BBO and LBO

Characterization of organic crystals for second-harmonic generation

Second-harmonic generation (SHG) is a common technique with many applications. Common inorganic single-crystalline materials used to produce SHG light are effective using short IR/visible wavelengths but generally do not perform well at longer, technologically relevant IR wavelengths such as 1300, 1550, and 2000 nm. Efficient SHG materials possess many of the same key material properties as terahertz (THz) generators, and certain single-crystalline organic THz generation materials have been reported to perform at longer IR wavelengths. Consequently, this work focuses on characterizing three efficient organic THz generators for SHG, namely, DAST (trans-4-[4-(dimethylamino)-N-methylstilbazolium] p-tosylate), DSTMS (4-N,N-dimethylamino-4'-N'-methylstilbazolium 2,4,6-trimethylbenzenesulfonate), and the recently discovered generator PNPA ((E)-4-((4-nitrobenzylidene)amino)-N-phenylaniline). All three of these crystals outperform the beta-barium borate (BBO), an inorganic material commonly used for SHG, using IR pump wavelengths (1200-2000 nm).

Broadband second-harmonic-generation in GdCOB crystals

Broadband second-harmonic-generation (SHG) in GdCOB crystals was demonstrated for the first time. Theoretical calculation and experiments for the type-I frequency doubling of GdCOB crystal was performed. The result revealed that the spectral retracing point of phase-matching angle was at around 1.65 µm. For broadband fundamental laser source tuning in the range of 1.55-1.7 µm, efficient SHG was realized, the highest conversion efficiency was 56%, and the output bandwidth reached 16 nm.

Shaping of picosecond laser pulses with THz intensity modulation in the infrared, visible, and ultraviolet ranges

The methods of shaping picosecond laser pulses with periodic intensity modulation tunable in frequency and depth are considered. Schemes for shaping modulated pulses "in-line" and with one output port are proposed. A picosecond modulation of the time envelope for IR laser pulses using a polarization interferometer is demonstrated experimentally. Shaping of modulated laser pulses of the UV range is shown by numerical modeling. The possibility to control the modulation depth of the fourth harmonic under the combined impact of material dispersion and nonlinear conversion in a classical collinear scheme of the fourth harmonic generation without distortion of the 3D pulse shape is demonstrated.

Green-Yellow-Orange-Red Spectral Range with Sum-Frequency Generation Using BIBO Crystal Pumped with an Optical Parametric Amplifier

In this letter, we show the broadband sum-frequency generation (SFG) in the Green-Yellow-Orange-Red spectral range using bismuth triborate, BiB3O6 crystal (BIBO) as a nonlinear material. We perform a noncollinear phase-matching configuration within the BIBO crystal using the remaining light behind the second harmonic generation stage and the infrared idler of an optical parametric amplifier (OPA). The obtained mixing radiation of ultrafast light sources to generate femtosecond pulses across the 520.5 to 742.5 nm region is observed. The SFG spectrum from a single-pass cross-correlation intensity over such visible range is shown. The SFG wavelengths as a function of the tunable wavelength idler OPA agree with the expectations of the parametric conversion condition and open the door to practical multi-beam or multi-color sum-frequency generators.

Investigation of spatio-temporal stretching in a duplex grating compressor

We employ the modified 6×6 matrix formalism to describe a pulsed Gaussian beam diffracted by a grating with arbitrary orientation. The matrix treatment is used to analyze the evolution of a pulsed beam propagating in a duplex grating compressor (DGC). For chirped pulse incidence, the inclination angle required in DGC setups will introduce several kinds of first-order spatio-temporal couplings (STCs). We found that temporal stretching due to spatial chirp is suppressed with enlarged beam diameter. Pulse-front tilt and residual frequency chirp in the compressed pulse will be eliminated simultaneously. Pulse with the transform-limited duration can be expected in ultra-intense and ultra-short pulse laser systems employing DGC.

Second-order nonlinear optical properties of bulk GeC polytypes, g-GeC and corresponding nanotubes: first-principles calculations

GeC nanotubes possess a strong second-order NLO response. Its origin is the high density of states near the VBM.