Cascading Of Second-order Nonlinearities Research Articles

Effective Kerr lens mode locking in Er3+:ZBLAN fiber laser with phase mismatched periodically poled lithium niobate

We theoretically introduce an effective Kerr lens mode locking concept to a polarization maintaining (PM) Er3+:ZBLAN fiber laser and generate a stable femtosecond pulse train at 2.76 µm. Phase-mismatched periodically poled lithium niobate (PPLN) is utilized to implement cascaded second order nonlinearities (CSN) for the effective Kerr lens mode locking. Furthermore, the CSN in the PPLN can be tuned to balance the huge fiber anomalous dispersion for femtosecond soliton formation in the mid-infrared regime. High coupling efficiency of light into fiber, shorter effective focal length of PPLN and larger effective nonlinear refractive index areessential for enhancing intracavity peak power and shortening pulse duration. The pulse could be compressed down to 311 fs with output pulse energy of 1.36 nJ and peak power of 3.6 kW. This mode locking method provides deep insight into direct generation of femtosecond fiber laser in mid-infrared regime.

Phase-matched second harmonic generation and cascaded nonlinearity in a Langmuir–Blodgett inverted waveguide of 2-docosylamino-5-nitropyridine

We discuss the results of our second harmonic generation (SHG) and nonlinear cascading experiments in organic waveguide. The waveguide is made of two identical Langmuir–Blodgett films with 2-docosylamino-5-nitropyridine. The thin film and waveguide characterization is presented with a detailed description of the experimental setup. An inverted waveguide is produced by a proper arrangement of the thin organic films. Using a tunable laser source the phase match at λ=1063 nm of the SHG is proved. The SHG power-corrected efficiency of 8.9% W−1 was measured. The cascading of second-order nonlinearities is characterized by means of interferometric measurements which consist of detecting a nonlinear phase shift of the fundamental in dependence on input intensity. The measured value of cascading n2 is 2.68×10−13 cm2/W.

All-optical switching based on cascading of second-order nonlinearities in a periodically poled titanium-diffused lithium niobate waveguide

We report efficient all-optical switching by using a periodically poled titanium-diffused lithium niobate (Ti:PPLN) waveguide. The periodically domain inversion of the Ti:PPLN waveguide is achieved by electric field poling. The switching is driven by the second-order nonlinear effect of the cascading of phase-matched sum-frequency-generation and difference-frequency-generation processes. It is found that about 12% of the signal is switched by a 20-W gate power.

Perturbative analysis of transverse effects of χ^(2) cascading in resonators

The transverse effects caused by second-harmonic generation and cascading of second-order nonlinearities on the self-consistent beams circulating in a resonator containing a nonlinear crystal are analyzed in a general and unified manner by use of a first-order perturbation theory. Various resonator configurations are considered, including those of practical relevance for generation of picosecond pulses by passive mode locking of solid-state lasers. The result is a closed form expression for self-induced loss modulation of the resonator. We compared the various resonators and modes of operation by numerically finding the maximum transmission modulation achievable and explicitly calculating for each of them the optimum phase mismatch and the optimum parameters of the Gaussian beam in the crystal.

Nd:YVO 4 laser mode locked by cascading of second order nonlinearities

Experimental results on an end pumped CW Nd:YVO 4 laser mode locked using cascading of second order nonlinearities in an intracavity KTP crystal are reported. The mode locking technique exploits the nonlinear transverse phase distortion arising during second harmonic generation and parametric back conversion and is demonstrated for the first time with a type II phase matched nonlinear crystal (KTP). Pulses of 6.8 ps have been obtained. For compensation of the group velocity mismatch in the nonlinear crystal a technique, whose effectiveness was previously only proved in combination with type I phase matching, has been demonstrated to be also successfully applicable with type II phase matching. This technique is based on the use of an intracavity birefringent crystal. The compensation method has also been applied to the same laser mode locked by the nonlinear mirror technique and pulses of comparable duration have been obtained.

Mode locking by cascading of second-order nonlinearities

We present a comprehensive theoretical and experimental study on a new passive mode-locking technique, called cascaded second-order nonlinearity mode locking (CSM), which exploits cascaded second-order nonlinearities to obtain large third-order susceptibilities from an intracavity second harmonic crystal. The nonlinear phase shift that originates in the nonlinear crystal is converted into a nonlinear amplitude modulation by a suitable intracavity aperture. A numerical model, based on a perturbative approach, allows the nonlinear loss modulation of resonators used for CSM to be calculated as a function of the resonator parameters and of the phase mismatch. The predictions of the model are confirmed by experiments performed on a CW Nd:YAG laser. The effects of group velocity mismatch and the limitations which it poses on the minimum achievable pulsewidth are analyzed both experimentally and theoretically.

Amplified ultrafast optical switching by cascading cascaded second-order nonlinearities in a polarization-gate geometry

We demonstrate amplified ultrafast all-optical switching of 250-fs pulses using two different types of cascaded second-order nonlinearities (CSNs) simultaneously in a simple polarization-gate geometry using a type II crystal. The first set of CSN processes has the effect of rotating the input-pulse polarization, yielding polarization gating. This signal pulse is then amplified by a second (different) set of CSN processes involving second-harmonic generation of the gate followed by a stimulated parametric down-conversion process. Using these “cascaded cascaded” second-order processes, we observe amplified switching with 320% efficiency and an on-off ratio of 6 × 10 5 in a 1-mm-thick crystal of BBO.

Self-starting mode locking of a cw Nd:YAG laser using cascaded second-order nonlinearities

The nonlinear mode variations induced by the equivalent third-order susceptibility resulting from cascaded secondorder nonlinearities in an intracavity lithium triborate crystal are exploited for mode locking of a cw Nd:YAG laser. The loss modulations are provided by a slit, as in the Kerr-lens mode-locking scheme. The mode-locking process is self-starting and produces nearly transform-limited pulses of 14-ps duration with 0.5-W average power.

Phase-controlled transistor action by cascading of second-order nonlinearities in KTP

We demonstrate a 4.6-to-1 modulation depth imposed on the fluence of an intense 1.06-microm picosecond pulse by varying the relative phase of a weak second-harmonic control pulse under near phase-matched conditions. This transistorlike action is based on quadratic nonlinearities in KTP.

All-optical phase controlled amplitude modulator

Based on the cascading of second-order nonlinearities, the authors propose a novel scheme for all-optical processing exploiting the tensorial nature of the second-order susceptibility. A weak phase-modulated signal can efficiently modulate the amplitude of a frequency-degenerate orthogonally polarised intense beam through coherent interaction via the generated second-harmonic. Device feasibility in lithium niobate is addressed.