Noncollinear Geometry Research Articles

Crater drilling enhancement obtained in parallel non-collinear double-pulse laser ablation

In order to investigate the double-pulse ablation mechanism, two parallel but non-collinear laser beams, delayed with respect to each other by 1 μs, were focussed on an aluminium sample, so that a lateral distance of 600 microns exists between the centres of the two craters and no superposition of the laser-ablation zones is present. The use of such configuration results in a signal and in a plasma mass enhancement with respect to the single-pulse case almost equal to that obtained in the double-pulse collinear case. However, such a non-collinear geometry evidences a much more effective drilling of the surface. Such unexpected drilling seems to be related to a hydrodynamic drainage out of aerosol and molten material, hindering its re-deposition in and around the crater.

Multi-terawatt chirped pulse optical parametric amplifier with a time-shear power amplification stage

We report on a compact and simple, broadband optical parametric chirped pulse amplifier system that amplifies femtosecond pulses directly from a titanium sapphire oscillator up to 2 TW power. Our system relies on a new technique - time shear - that improves the time overlap between the seed and pump pulses and, thus, improves the efficiency of the power amplification stage pumped with a ns laser. Parametric amplification was achieved in two stages: a multipass, noncollinear geometry preamplifier with a single beta-barium borate crystal, and a power booster stage incorporating three beta-barium borate crystals in the new time-shear design. Both stages were pumped with pulses from a commercial 10 Hz frequency doubled ns Nd:YAG laser. The system delivers 49 mJ pulses with a temporal width of 23 fs and its overall conversion efficiency after pulse compression is 10%.

Simultaneously phase-matched blue and red light generation using BIBO

BiB3O6 has been found to be simultaneously phase matchable for sum-frequency generation at 0.4627 and 0.6260 microm by mixing the outputs of a 0.5321 microm pumped parametric oscillator with the fundamental source at 1.0642 microm. The simultaneous blue and red light generation is achieved under the temperature-insensitive phase-matching condition, and the relative strength of blue and red light can be controlled by changing the effective nonlinear constants through the azimuth angle. In addition, wide wavelength tuning of the simultaneous phase matching is obtained by the use of a noncollinear geometry, enabling a compact red-green-blue laser system based on the powerful solid-state laser.

Broadband tunable pulses in quasi-phase-matched crystal based optical parametric amplification

The influence of grating period and noncollinear geometry on the broadly tunable bandwidth of optical parametric amplification are investigated theoretically and numerically for quasiphasematched crystal. The concept of maximum grating period is proposed to achieve the phase matching and groupvelocity matching simultaneously in a wide range. By employing the maximum grating period, geometry Ⅰ is recommended due to the much wider signal tunable range compared with geometry Ⅱ. An expression is proposed to calculate the maximum grating period for congruent periodically poled LiNbO3 with 800 nm pump wave. A feasible scheme is presented to determine the working temperature and noncollinear angle α, maximize the tunable range and simplify the tuning by rotating angle θ only. Finally, the parametric bandwidth is studied with consideration of the influences of the maximum grating period and noncollinear geometry.

PPLN晶体中不同非共线结构光参量放大过程的带宽与增益特性

PPLN晶体中不同非共线结构光参量放大过程的带宽与增益特性

ANGULAR DISPERSION IN SPONTANEOUS PARAMETRIC DOWN CONVERSION: A TOOL TO GENERATE NARROW TEMPORAL BIPHOTONS AND PURE HERALDED SINGLE PHOTONS

In this paper, we describe how introducing angular dispersion into the pump beam and the downconverted photons in spontaneous parametric downconversion allows us to manipulate the joint spectrum of the paired photons. In particular, when collinear geometries are used, we demonstrate an increase of the photons' bandwidth and discuss the implications of this method for the generation of narrow temporal Fourier transform limited biphotons. Additionally, we describe the situation in which angular dispersion is combined with noncollinear geometries. In this case, a full control of the joint spectrum is achieved and heralded pure single photons with controllable bandwidth can be obtained.

Inherently phase-stable coherent two-dimensional spectroscopy using only conventional optics

We introduce an inherently phase-stable setup for coherent two-dimensional femtosecond spectroscopy in noncollinear box geometry using only conventional beam splitters, mirrors, and delay stages. Avoiding diffractive optics, pulse shapers, and active phase-locking loops, our spectroscopy setup is simple, robust, and works for ultrabroad bandwidths in all spectral regimes (infrared, visible, and ultraviolet).

Four wave mixing at air-dielectric interfaces with a femtosecond laser excitation

In this article we report our experimental results on non collinear four-wave mixing (FWM) at air-dielectric interfaces. We generated FWM signal from the two interfaces of a 1mm thick fused silica slide with air using two 800 nm, 100 fs pump pulses in non-collinear pump-probe type geometry. We observe that there is a maximum peak shift of approximately 1.5 nm in FWM signals corresponding to the two interfaces of the same silica slide. Further, we find that the intensity of FWM signal observed at air to silica interface is less than that from silica to air interface. We briefly elaborate on this observation with systematic study of FWM in fused silica.

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.

Substantial gain enhancement for optical parametric amplification and oscillation in two-dimensional χ^(2) nonlinear photonic crystals

We have analyzed optical parametric interaction in a 2D NPC. While in general the nonlinear coefficient is small compared to a 1D NPC, we show that at numerous orientations a multitude of reciprocal vectors contribute additively to enhance the gain in optical parametric amplification and oscillation in a 2D patterned crystal. In particular, we have derived the effective nonlinear coefficients for common-signal amplification and common-idler amplification for a tetragonal inverted domain pattern. We show that in the specific case of signal amplification with QPM by both G(10) and G(11), symmetry of the crystal results in coupled interaction with the corresponding signal amplification by G(10) and G(1,-1). As a consequence, this coupled utilization of all three reciprocal vectors leads to a substantial increase in parametric gain. Using PPLN we demonstrate numerically that a gain that comes close to that of a 1D QPM crystal could be realized in a 2D NPC with an inverted tetragonal domain pattern. This special mechanism produces two pairs of identical signal and idler beams propagating in mirror-imaged forward directions. In conjunction with this gain enhancement and multiple beams output we predict that there is a large pulling effect on the output wavelength due to dynamic signal build-up in the intrinsic noncollinear geometry of a 2D NPC OPO.

Generation of ultra-broadband pulses in the near-IR by non-collinear optical parametric amplification in potassium titanyl phosphate

Non-collinear optical parametric amplification in potassium-titanyl phosphate (KTP) pumped with 800 nm pulses is reported. Broadband phase matching is achieved with non-collinear geometry and a slightly divergent signal seed. This enables a gain bandwidth up to approximately 2500 cm(-1) in near-IR region. Introducing a chirp into the pump pulse makes it possible to amplify the white light seed in a broad spectral region from approximately 1050 to approximately 1400 nm simultaneously. Pulse compression to sub-40 fs is readily achieved, while the spectrum should support approximately 8.5 fs pulses. Angular dispersion of the broadband output is discussed.

Non-collinear quasi-phase-matched linear electro-optic effect in periodically poled LiNbO3and its applications

The non-collinear quasi-phase-matched (QPM) linear electro-optic effect in periodically poled LiNbO3 (PPLN) is investigated in this paper. It is found that the non-collinear geometry can provide an efficient way of reaching the QPM condition for a small phase mismatching PPLN at normal incidence, and higher conversion efficiency can be achieved by adjusting the non-collinear angle at a given wavelength, temperature and applied electric field. The numerical results show that the QPM condition is very sensitive to the non-collinear angle and the wavelength, having potential applications in tunable optical filters.

Broad-Bandwidth Semi-Noncollinear Optical Parametric Amplification in Periodically Poled LiNbO3 Based on Tilted Quasi-Phase-Matched Gratings

On the basis of noncollinear optical parametric amplification in periodically poled lithium niobate (PPLN) which is realized by quasi-phase matching (QPM) technology, we consider the possibility of semi-noncollinear phase matching between collinear and noncollinear geometries by tilting a PPLN-crystal's parallel grating at a sure angle. Numerical simulation with proper parameters shows that we can achieve a broader optical parametric amplification (OPA) bandwidth than that of noncollinear geometry. About 121 nm at a signal wavelength of 800 and 70 nm at a signal wavelength of 1064 nm under optimal conditions are obtained when the crystal length is 9 mm.

Sum and difference frequency generation of white light continuum with the ps pulses of Nd+3:YAG laser in a thick BBO crystal

The white light continuum (WLC) generated in water/D2O mixture by pumping with the fundamental of ps Nd+3:YAG laser has been used as a variable frequency source for the sum frequency generation as well as for its amplification. 35ps long pulses with 8mJ energy at 1064nm were mixed collinearly with the WLC generated by the same laser beam in a 20mm thick BBO crystal. The obtained tunable output has been identified as the sum frequency between the fundamental and a portion of the WLC with the required phase matching. Theoretical simulations are also given along with a few initial experiments to use this combination for the difference frequency generation (optical parametric amplification) under non-collinear geometry.

High-power femtosecond infrared laser source based on noncollinear optical parametric chirped pulse amplification

The optical parametric chirped pulse amplication (OPCPA) concept has been extended to the infrared range, providing a new approach, to our knowledge, to high-power femtosecond pulses in the 1.5 μm range. This amplifier is based on 1.05 μm pumping of bulk KTiOAsO4 with broadband phase matching in a noncollinear geometry. The output pulse energy of 1 mJ was generated with 50 nm of bandwidth by 3.8 mJ of pump energy from a 100 ps, 1 kHz Nd:YLF amplified laser. Total gain of 108 was achieved in three stages with 32% conversion of the pump energy in the final amplifier stage. Amplified pulses were compressed to 130 fs with peak intensities of 3.85 GW.

Facile collection of two-dimensional electronic spectra using femtosecond pulse-shaping Technology

This letter reports a straightforward means of collecting two-dimensional electronic (2D-E) spectra using optical tools common to many research groups involved in ultrafast spectroscopy and quantum control. In our method a femtosecond pulse shaper is used to generate a pair of phase stable collinear laser pulses which are then incident on a gas or liquid sample. The pulse pair is followed by an ultrashort probe pulse that is spectrally resolved. The delay between the collinear pulses is incremented using phase and amplitude shaping and a 2D-E spectrum is generated following Fourier transformation. The partially collinear beam geometry results in perfectly phased absorptive spectra without phase twist. Our approach is much simpler to implement than standard non-collinear beam geometries, which are challenging to phase stabilize and require complicated calibrations. Using pulse shaping, many new experiments are now also possible in both 2D-E spectroscopy and coherent control.

Spatial–temporal frequency band of optical parametric amplifier

The spatial–temporal frequency band of optical parametric amplifier for collinear as well as for noncollinear phase-matching is analyzed taking into account angular dispersion of amplified pulsed beam. The simple formulae are derived which make possible determination of the largest frequency bands of parametric amplifiers in noncollinear geometry. It has been demonstrated that a shape of the spatial–temporal frequency band of optical parametric amplifier essentially depends on pump and signal wavelengths, and certain angular dispersion as well as proper beamwidth of signal pulse enable amplification of ultrashort pulses with duration of a few femtoseconds.

Raman and Thompson regimes of amplification in a wiggler with noncollinear laser and electron beams

The collective and single-electron amplification regimes of a noncollinear free-electron laser (FEL) are studied within the framework of dispersion equations. In the limit of small-signal gain the growth rates and the conditions for self-amplified excitations are found for the collective (Raman) and single-electron (Thompson) regimes. The Raman regime is shown to be preferable for the coherent spontaneous second harmonic generation by ultrarelativistic electron beams. Raman excitations in a noncollinear FEL, e.g., in an FEL without inversion, are favored by the noncollinear geometry of the electron and the laser beams, and by the relativity of the beam electrons.

Group-velocity-mismatch compensation in cascaded third-harmonic generation with two-dimensional quasi-phase-matching gratings

A novel scheme to achieve broadband cascaded third-harmonic generation by use of two-dimensional quasi-phase-matching gratings is proposed. Intrinsic group-velocity mismatch is compensated by the pulse front tilt in noncollinear interaction geometry. The presented scheme enables broadband third-harmonic generation in a single device of long interaction length, which reduces the operation intensity dramatically.

Numerical simulations of optical parametric amplification cross-correlation frequency-resolved optical gating

We perform numerical simulations of cross-correlation frequency-resolved optical gating with the nonlinearities, optical parametric amplification, and difference-frequency generation for measuring broadband pulses. We show that use of a noncollinear beam geometry that matches the group velocities of the pump, signal, and idler pulses permits use of relatively thick crystals for high gain without significant distortion in the measured trace, yielding bandwidths of ~100 nm.