Four-wave Optical Parametric Amplification Research Articles

Four-Wave Optical Parametric Amplification in a Raman-Active Gas

Four-wave optical parametric amplification (FWOPA) in a Raman-active medium is experimentally investigated by use of an air-filled hollow fiber. A femtosecond pump pulse shorter than the period of molecular motion excites the coherent molecular motion of the Raman-active molecules during the parametric amplification of a signal pulse. The excited coherent motion modulates the frequency of the signal pulse during the parametric amplification, and shifts it to lower frequencies. The magnitude of the frequency redshift depends on the pump intensity, resulting in intensity-dependent spectral characteristics that are different from those in the FWOPA induced in a noble-gas-filled hollow fiber.

Parametric amplification-assisted cascaded four-wave mixing for ultrabroad laser sideband generation in a thin transparent medium

We demonstrate distinct sets of broadband up-converted multicolor array (BUMA) signals in a thin transparent medium with an intense 800 nm fundamental pulse (FP) and a weak, unfiltered super-continuum white light (SCWL) in a crossing geometry. Upon varying the time delay between the two incident laser pulses, continuously tunable BUMA signals in the visible to near-IR range sequentially emerge on either side of the FP, in both BBO crystal and BK7 glass. Through numerical calculations at intrinsic phase-matching conditions, the BUMA signals on the SCWL side are shown to arise from the interaction mainly between χ(3)-based four-wave optical parametric amplification and cascaded four-wave mixing processes. The temporally controllable broadband BUMA signals with amplification and tunability all in one thin transparent medium are highly suitable for ultrafast laser spectroscopy and optical communication networks.

Optical parametric amplification of a supercontinuum in a gas

Amplification of supercontinuum light via four-wave optical parametric amplification in a gas-filled hollow fiber is investigated. By pumping with a femtosecond pulse in the near-infrared, amplification was observed in the wavelength range 500–700 nm, with an amplification gain up to 100. The amplification bandwidth obtained here supports sub-10-fs pulse durations. The wavelength and gas-pressure dependence of the amplification gain in this regime significantly differ from those predicted from only the linear phase mismatch. The nonlinear phase mismatch, arising from nonlinear phase modulations induced by a pump pulse, dominates the features observed for the amplification, i.e., a low phase-matching pressure and an amplification gain depending on wavelength. To investigate the effect of phase modulations on the parametric amplification, numerical analysis and simulations are used to reproduce the measured wavelength dependence of the amplification gain.

Generation of broadly tunable sub-30-fs infrared pulses by four-wave optical parametric amplification

We report on the generation of sub-30-fs near-IR light pulses by means of broadband four-wave parametric amplification in fused silica. This is achieved by frequency downconversion of visible broadband pulses provided by a commercial blue-pumped beta-barium borate crystal-based noncollinear optical parametric amplifier. The proposed method produces the IR idler pulses with energy up to ∼20 μJ and tunable in wavelength from 1 to 1.5 μm. The shortest pulse duration is 17.6 fs, measured at 1.2 μm.

Generation of tunable infrared femtosecond pulses via parametric visible-to-infrared frequency conversion

We propose two methods for ultrashort pulse parametric visible-to-infrared frequency conversion, that are directly applied to extend the tuning range of a commercial Ti:sapphire laser-noncollinear optical parametric amplifier system. The first method is based on broadband noncollinear four-wave optical parametric amplification in fused silica, and the second is based on cascaded three-wave parametric interaction in a single BBO crystal. The proof-of-principle experiments demonstrate generation of sub30-fs, 20 µJ pulses, broadly tunable across the infrared (1‐3 µm) spectral range.

Generation and amplification of tunable multicolored femtosecond laser pulses by using cascaded four-wave mixing in transparent bulk media.

We have reviewed the generation and amplification of wavelength-tunable multicolored femtosecond laser pulses using cascaded four-wave mixing (CFWM) in transparent bulk media, mainly concentrating on our recent work. Theoretical analysis and calculations based on the phase-matching condition could explain well the process semi-quantitatively. The experimental studies showed: (1) as many as fifteen spectral up-shifted and two spectral down-shifted sidebands were obtained simultaneously with spectral bandwidth broader than 1.8 octaves from near ultraviolet (360 nm) to near infrared (1.2 μm); (2) the obtained sidebands were spatially separated well and had extremely high beam quality with M2 factor better than 1.1; (3) the wavelengths of the generated multicolor sidebands could be conveniently tuned by changing the crossing angle or simply replacing with different media; (4) as short as 15-fs negatively chirped or nearly transform limited 20-fs multicolored femtosecond pulses were obtained when one of the two input beams was negatively chirped and the other was positively chirped; (5) the pulse energy of the sideband can reach a μJ level with power stability better than 1% RMS; (6) broadband two-dimensional (2-D) multicolored arrays with more than ten periodic columns and more than ten rows were generated in a sapphire plate; (7) the obtained sidebands could be simultaneously spectra broadened and power amplified in another bulk medium by using cross-phase modulation (XPM) in conjunction with four-wave optical parametric amplification (FOPA). The characterization showed that this is interesting and the CFWM sidebands generated by this novel method have good enough qualities in terms of power stability, beam quality, and temporal features suited to various experiments such as ultrafast multicolor time-resolved spectroscopy and multicolor-excitation nonlinear microscopy.

Simultaneous compression and amplification of a laser pulse in a glass plate

We demonstrated a novel method of simultaneous compression and amplification of a weak laser pulse in a glass plate using cross-phase modulation in conjunction with four-wave optical parametric amplification that was pumped by an intense femtosecond pulse. A proof-of-principle experiment succeeded in smooth broadening of the weak pulse spectrum by a factor of about three and simultaneously amplifying the pulse energy by more than three times. By using chirped mirrors to compensate the dispersion, the weak pulse was compressed from 22.6 fs to 12.6 fs. Furthermore, the output spectrum of seed pulse could be tuned by varying the delay of the intense pump pulse with respect to the weak seed pulse. This method can also be used for simultaneous spectral broadening of several weak beams with different wavelength at the same time.

Broadband four-wave optical parametric amplification in bulk isotropic media in the ultraviolet

We report on four-wave optical parametric amplification of the ultrashort ultraviolet light pulses in bulk fused silica and CaF 2 . Exact phase-matching in these isotropic media is achieved by means of non-collinear interaction with cylindrical beam focusing. Four-wave optical parametric amplifier efficiently operates in the UV spectral range with 1-ps laser pulses, delivering amplified signal energy exceeding 50 μJ using millijoule pump pulses in the visible (527 nm). Results of scanning of the parametric gain profile suggest that broad amplification bandwidth as wide as ∼20 nm (at FWHM) under these experimental settings is achieved, which might support amplification of sub-10-fs ultraviolet pulses with central wavelength around 330 nm. It is also shown experimentally and verified theoretically that the parametric gain profile exposes a distinct inhomogeneity and its bandwidth notably broadens due to effects of self- and cross-phase modulation imposed by the intense pump beam.

Ultrafast Four-Wave Optical Parametric Amplification in Transparent Condensed Bulk Media

We present a short overview of recent advances in ultrashort pulse four-wave optical parametric amplification in transparent condensed bulk media with Kerr nonlinearity. Highly efficient (10% to 15% pump-to-signal energy conversion) four-wave optical parametric amplification in water and fused silica is experimentally demonstrated. The amplification process highly benefits from 1-dimensional spatial soliton propagation regime, which sets in under proper combination of cylindrical beam focusing and noncollinear phase matching geometry with millijoule pumping. Under these operating conditions, strong four-wave coupling quenches catastrophic beam break-up and filamentation, and the setup operates reasonably below the damage threshold of the nonlinear medium. The proposed methodology offers a number of advantages as compared to guided-wave configurations in gaseous media.

High-energy broadband four-wave optical parametric amplification in bulk fused silica

Efficient broadband four-wave optical parametric amplification in bulk Kerr medium (fused silica) is demonstrated by means of noncollinear phase matching and cylindrical focusing geometry without the onset of beam breakup and filamentation. Amplified signal energy as high as 180 microJ with 1 ps, 1.8 mJ pumping at 1,055 nm is achieved with pump-to-signal energy conversion close to 10%. More than 70 nm FWHM parametric gain bandwidth around 740 nm is demonstrated without imposing angular dispersion on the frequency components of the broadband seed signal.

Highly efficient four-wave parametric amplification in transparent bulk Kerr medium

We report on highly efficient four-wave optical parametric amplification in a water cell pumped by an elliptically shaped, ultrashort pulsed laser beam under non-collinear phase-matching configuration. Energy conversion from pump to parametric waves as high as 25 % is obtained owing to the achievement of 1-dimensional spatial-soliton regime, which guarantees high intensity over a large interaction length and ensures high beam quality.

Four-Wave Parametric Amplification of Rabi Sidebands in Sodium

Four-wave optical parametric amplification enhanced by the ac Stark effect has been observed, with the use of a dye laser tuned near the ${D}_{2}$ line of sodium. This process leads to the generation of sidebands displaced from the laser frequency by the generalized Rabi frequency. Under certain experimental conditions, the emitted radiation is in the form of a cone surrounding the transmitted laser beam. A theoretical model that describes these effects is presented.