Noncollinear Sum-frequency Generation Research Articles

Control of laser-plasma instabilities by non-collinear polychromatic light

Normal broadband lasers with collinear polychromatic components have immense potential for mitigating laser plasma instabilities (LPIs). However, the projection complexity of collinear polychromatic light (CPL) is a significant challenge owing to the demand for a large bandwidth and beamlet number. Here, we propose a theoretical LPI model and optical design for non-collinear polychromatic light (NCPL), which has a small angle ∼4∘ and large frequency difference ∼1% between the double-color beamlets. LPI models of the NCPL demonstrate a decoupling threshold for the shared daughter waves under a multibeam configuration. Compared with the CPL, the wavevector couplings of LPIs are further reduced by the introduced angle. Therefore, both the growth rate and saturation level of LPIs are greatly mitigated by using the NCPL. The two- and three-dimensional simulation results indicate that the NCPL reduces the absolute and convective decoupling thresholds of the CPL and is sufficient to effectively mitigate the reflectivity, hot-electron generation, and intensity of cross-beam energy transfer. An optical design for the efficient generation of ultraviolet NCPL has been presented based on the unsaturated optical parametric amplification and non-collinear sum-frequency generation.

Mixing Ince–Gaussian modes through sum-frequency generation

We present a nonlinear mixing study of Ince–Gaussian (IG) beams in non-collinear sum-frequency generation, completing the fundamental analysis of all three families of paraxial wave equation solutions under this nonlinear process. Through theoretical and experimental results, we consider the nonlinear mixing of even and odd IG modes, and transition between the paraxial modes by controlling the eccentricity parameter ϵ and helical IG modes possessing arbitrary orbital angular momentum. Additionally, the selection rule of IG modes in the nonlinear mixing processes is determined. This work is important for optical communications and quantum protocols.

Pulse contrast enhancement via non-collinear sum-frequency generation with the signal and idler of an optical parametric amplifier

We outline an approach for improving the temporal contrast of a high-intensity laser system by >8 orders of magnitude using noncollinear sum-frequency generation with the signal and idler of an optical parametric amplifier. We demonstrate the effectiveness of this technique by cleaning pulses from a millijoule-level chirped-pulse amplification system to provide >1012 intensity contrast relative to all prepulses and amplified spontaneous emission >5 ps prior to the main pulse. The output maintains percent-level energy stability on the time scales of a typical user experiment at our facility, highlighting the method's reliability and operational efficiency. After temporal cleansing, the pulses are stretched in time before seeding two multipass, Ti:sapphire-based amplifiers. After re-compression, the 1 J, 40 fs (25 terawatt) laser pulses maintain a >1010 intensity contrast >30 ps prior to the main pulse. This technique is both energy-scalable and appropriate for preparing seed pulses for a terawatt- or petawatt-level chirped-pulse amplification laser system.

Coherent beam combining of pulsed fiber amplifiers by noncolinear sum-frequency generation.

In this Letter, we demonstrate coherent beam combining of laser pulses, amplified in four separate Yb-doped fiber amplifiers, by using the second-order nonlinear crystal as a combining element. Active phase control was used, and pulses with 240ps duration were combined in a noncollinear sum-frequency generation configuration. Conversion/combining efficiency up to 49% was achieved. The maximum pulse energy of 108 μJ and average power of 97W were achieved in the combined beam at 519nm.

Retaining 3D shape of picosecond laser pulses during optical harmonics generation.

Collinear and noncollinear sum-frequency generation of broadband laser pulses with angular and frequency chirp is considered. The conditions of minimal distortions of 3D ellipsoidal intensity distribution of triangular chirped femtosecond pulses during generation of the second, third, and fourth harmonics of a Ti-Sa laser in LBO, BBO, and KBBF crystals are found using numerical methods. The efficiency of conversion from the fundamental to the fourth harmonic (45%) is higher than to the third harmonic (20%), and the distortions of intensity distribution are less.

Quantum temporal imaging with squeezed light

We consider a simple quantum temporal imaging system on the basis of a time lens implemented by a parametric nonlinear optical process with a chirped pump. We review the main results of the modal theory of temporal imaging, developed recently by us. We illustrate this theory by a concrete example of type-I non-collinear sum-frequency generation process, where the phase matching is limited by the temporal walk-off of the signal and the idler waves. We have shown that the temporal modal functions of such an imaging system are chirped Hermite-Gauss functions.

Vibrational Spectrum of an Excited State and Huang-Rhys Factors by Coherent Wave Packets in Time-Resolved Fluorescence Spectroscopy.

Coherent nuclear wave packet motions in an electronic excited state of a molecule are measured directly by time-resolved spontaneous fluorescence spectroscopy with an unprecedented time resolution by using two-photon absorption excitation and fluorescence upconversion by noncollinear sum frequency generation. With an estimated time resolution of approximately 25 fs, wave packet motions of vibrational modes up to 1600 cm-1 are recorded for coumarin 153 in ethanol. Two-color transient absorption at 13 fs time resolution are measured to confirm the result. Vibrational displacements between the ground and excited states and Huang-Rhys factors (HRFs) are calculated by quantum mechanical methods and are compared with the experimental results. HRFs calculated by density functional theory (DFT) and time-dependent DFT reproduce the experiment adequately. This fluorescence-based method provides a unique and direct way to obtain the vibrational spectrum of a molecule in an electronic excited state and the HRFs, as well as the dynamics of excited states, and it might provide information on the structure of an excited state through the HRFs.

Numerical simulation analysis of high efficient SFG and color separation in far field in high power laser facility based on noncollinear phase matching by KDP crystal

Asymmetric property of wedge lens in 3 optical path which is used as frequency separation, and focusing element is considered to be an unfavourable factor for target alignment in inertial confinement fusion (ICF). Furthermore, the thickness of wedge lens in 3 optical path will lead to laser induced damage inevitably. For the purpose of scheme improvement of final optical assembly, types I and II noncollinear sum frequency generation in KDP crystal at room temperature are discussed based on nonlinear coupled wave theory. As illustrated by simulated result, in addition to type II collinear SFG used in ICF recently, 351 nm (3) waves can be generated by type I or II noncollinear SFG process. This method can realize color separations of , 2, 3 in far field without asymmetric element such as wedge lens and posses adequate tolerance of matching angle corresponding to the high efficiency conversion. As calculated, for type I SFG, when the noncollinear angle is in the interval from 0 to 19.99, phase matching condition can be satisfied in KDP crystal. The noncritical phase matching angle 3 is 90 and the corresponding noncollinear angle is about 19.99. The tolerance of mismatching angle is about 20 mrad. For type II SFG, the noncollinear angle interval that can satisfy phase matching process is about 0-13.55. Like type I SFG, there is also an noncritical solution in type II process whose matching angle is about (3) = 86.53. Because of the smaller effective nonlinear coefficient in this case, high efficiency conversion needs about 5 cm thick SFG crystal under 1 GW/cm2. Correspondingly, tolerance of mismatching angle is about 20 mrad. Because of the harsh tolerance of noncollinear angle between and 2 and for the purpose of compactness of final optical assembly, another method of noncollinear SFG is proposed: a piece of silica wedge with 12 wedged angle is mounted behind the SHG crystal in order to produce a 3.5 mrad intersection angle between and 2, and after type II noncollinear SFG process, , 2, 3 will be frequency separated in far field automatically by using thin lens. The tolerance of incident angle corresponding to high efficient conversion is about 1.0 mrad. This scheme can improve the the final optical assembly used recently.

非共线和频过程中的表面散射杂散光分析

非共线和频过程中的表面散射杂散光分析

Ultrafast time-resolved fluorescence by two photon absorption excitation

We report a time-resolved fluorescence apparatus utilizing fluorescence upconversion by noncollinear sum frequency generation and two photon absorption as an excitation. Near perfect time-resolution is achieved with 20 fs pulses to give the instrument response of 33 fs (FWHM) over the entire fluorescence wavelength for a 100 microm thick mixing crystal. Through experiments and numerical simulations, it is shown that 40 fs time-resolution can be obtained even for a 580 microm thick mixing crystal at a fluorescence wavelength longer than 500 nm.

Non-collinear sum-frequency generation of femtosecond pulses in a micro-structured β-BaB_2O_4 crystal

Sum-frequency generation of femtosecond pulses by noncollinear phase matching in a micro-structured beta-BaB(2)O(4) crystal has been investigated. A 1D relief grating was recorded in the surface of a beta-BaB(2)O(4) crystal by direct irradiation with femtosecond pulses. Groove dimensions of 1 mum width and 200 nm depth were obtained for the recording parameters. This micro-structured crystal was used for generating ultraviolet pulses (265 nm) by noncollinear sum-frequency generation of the fundamental and the second harmonic of a Ti:Sapphire femtosecond laser system. Effective group-velocity matching between the incident pulses can be achieved for certain noncollinear processes in a compact way. The application of such device to intensity cross-correlation measurements of the second-harmonic pulse was shown.

Analysis of broadband third harmonic generation with non-collinear angular dispersion in KDP crystals

A new scheme with non-collinear sum frequency generation (SFG) process of broadband third harmonic generation (THG) with two KDP crystals (one doubler and one mixer) using angular dispersion was proposed. The principle of broadband harmonic generation with non-collinear angular dispersion was presented. The comparison between the schemes of non-collinear and collinear SFG process was performed. The effects of the angular dispersion on the conversion efficiency, the pulse shape and the spectrum of the third harmonic field were discussed. The results show that, if proper angular dispersion is added to the fundamental and the second harmonic field outside the mixing KDP crystal, respectively, the broadband third harmonic conversion efficiency can be improved significantly. However, the difficulty of this scheme arises due to the requirement of two gratings with different angular dispersion outside the mixer. With the new scheme, it can be simpler that only one grating is needed to realize the broadband phase matching in the non-collinear SFG process. Although the fundamental and the second harmonic field inside the mixing crystal are non-collinear except the center wavelength, a blazing grating with proper angular dispersion for the fundamental field (twice as that for second harmonic field) can yield the well compensation for phase mismatching in the SFG process. Consequently, the conversion efficiency and the characteristics of the third harmonic field for the broadband third harmonic generation can be improved significantly.

Probing resonant nonlinearities in organic materials using photonic-crystal fiber frequency converters

Specially designed photonic-crystal fiber frequency converters of ultrashort laser pulses are shown to be ideally suited for probing resonant nonlinearities in organic materials. Photonic-crystal fibers used in our experiments provide an efficient frequency upshifting of femtosecond pulses of 1.25-μm Cr: forsterite laser radiation, generating broadband radiation within the 570–700-nm wavelength range. This radiation is then employed to probe the quadratic nonlinearity of a poled azopolymer film through noncollinear sum-frequency generation.

Noncollinear phase matching in fluorescence upconversion

We investigate noncollinear sum-frequency generation in a time-resolved fluorescence upconversion experiment to eliminate group-velocity mismatch (GVM), a major mechanism that deteriorates time resolution. The noncollinear geometry inherently causes phase-front mismatch (PFM) that also spoils time resolution. The effects of GVM and PFM on the time resolution are studied by numerical calculations and experiments. Based on the investigation, a fluorescence upconversion apparatus with time resolution better than 45 fs (FWHM) is demonstrated.

Compression of pulses of a few optical cycles through harmonic generation

Pulse compression through noncollinear sum-frequency generation in β-barium borate crystals is investigated. With dispersion to all orders taken into account, numerical calculations, carried out in the frequency domain, were performed for input pulse durations ranging from 10 to 50 fs. Fundamental pulses of a 10-fs duration at 800 nm were compressed down to 2.5 fs while a 2.5-fs second-harmonic signal was generated.

Measurement of Ultra-short Pulse-width by Using Noncollinear Sum-Frequency Generation

The third-order correlation function G(3) (0, τ) can be measured by using the method of noncollinear sum-frequency, by which the pulse-width of the ultra-short pulse light produced by mode-locked laser is deduced to be 35 ps. This result is the same as that by other standrd method.

A technique for the calculation of phase-matching angle for type-II noncollinear sum-frequency generation in negative uniaxial crystals

A technique of predicting the phase-matching angle for noncollinear sum-frequency mixing involving two extraordinary rays and one ordinary ray in a negative uniaxial crystal is described, and predicted results are experimentally verified. Good agreement between predicted and experimental results gives the technique a firm footing, thereby introducing a very simple relation correlating the noncollinear angle with the phase-matching angles of the interacting beams.

Sum frequency beam analysis for the determination of the temporal characteristics of ultrashort light pulses

An extension of the single-shot second harmonic beam method proposed earlier for picosecond pulse duration measurements is presented for the case of two incident pulses of differing frequencies, durations and transverse sizes. The solution of the wave equation for noncollinear sum frequency generation in a nonlinear crystal by two Gaussian, spatially limited ultrashort pulses is given. It is shown that the width (τ 1 2 +τ 2 2 )1/2 of the temporal cross-correlation function of the two pulses can be deduced from the spatial energy distribution of the sum frequency beam. The method can be used e.g. in the case of a relatively weak secondary pulse obtained in some nonlinear processes. Preliminary experimental results demonstrating the possibilities offered by the method are presented.