Picosecond Pulse Trains Research Articles

Optical Dynamics of Picosecond Pulse Trains in Aluminum and Zinc Tetracarboxy-Phthalocyanines

Optical Dynamics of Picosecond Pulse Trains in Aluminum and Zinc Tetracarboxy-Phthalocyanines

Harnessing tin phthalocyanine for ultrafast mode-locking in an erbium-doped fiber laser

We present the first demonstration, to the best of our knowledge, of a mode-locked erbium-doped fiber laser (EDFL) employing tin phthalocyanines (SnPc) as a saturable absorber (SA). The investigated SA exhibits a notable modulation depth of 18.6%, fabricated via a simple, cost-effective method, wherein the SnPc compound is embedded into a polyvinyl alcohol (PVA) film. Integration of this thin film into the EDFL cavity facilitates the generation of output pulses with a repetition rate of 0.96 MHz and a pulse duration of 2.68 ps. The frequency spectrum showcases a signal-to-noise ratio of up to 73.2 dB, affirming the stability of the mode-locking operation. Operating at a wavelength of 1531.7 nm, this picosecond pulse train holds significant promise for diverse applications, including high-precision optical metrology, frequency-comb generation, and broadband absorption spectroscopy.

Optical properties of meso-tetra(sulphonatophenyl) porphyrins (TPPS 4) and their Fe 3+, Mn 3+, Zn 2+ complexes with different pH values studied using by picosecond pulse trains

Applying picosecond pulse trains propagating in meso-tetra(sulphonatophenyl) porphyrins and their Fe 3+, Mn 3+, Zn 2+ complexes, we studied the nonlinear dynamics at different pH values. The pulse train at wavelength 532nm is comprised of 20 subpulses with 70ps width and 13ns spacing. We simplified the energy structures of porphyrins and metalloporphyrins to five-level models. In solving coupled rate equations and two-dimensional paraxial field, we used Crank-Nicholson numerical method to do the calculations. The results revealed that in irregular metalloporphyrins with central paramagnetic ion Mn 3+ or Fe 3+, the central ion would act as electron acceptor, which leads to charge transfer of unpaired metal electron to the porphyrin ring π conjugated system, and strengthen the spin–orbit coupling of electronic systems and weaken the transition prohibition between electronic states in porphyrins. However regular metalloporphyrins with central diamagnetic ion Zn 2+ has similar optical properties to free base porphyrins, and Zn 2+ TPPS 4 has much longer excited state lifetimes and slower intersystem crossing. In solutions, hydrogen bond would be formed to porphyrin, which can change the transitions of π electrons and thus the charge transfer can be strengthened in the porphyrin ring. In weak intensity region with linear absorption, nonprotonated porphyrins with high pH value show better optical limiting (OL) effect. Conversely in high intensity region, protonated porphyrins with low pH value show better OL effect. Besides, increasing interaction distances of porphyrins and metalloporphyrins with laser pulses is another important factor to raise the OL effects.

Integrated thin-film lithium niobate electro-optic frequency comb for picosecond optical pulse train generation

In recent years, high-performance thin-film lithium niobate (TFLN) electro-optic (EO) modulators boost the fast development of highly integrated, low loss, and large comb spacing EO frequency combs. Furthermore, ultra-short optical pulse trains (USOPTs) can be generated by the temporal domain compression of the optical frequency comb, which play an essential role in photonic sampling analog-to-digital conversion. Here, we demonstrate a flat and broadband EO frequency comb based on a packaged TFLN chip including a monolithic integrated intensity modulator, a phase modulator, and edge couplers. The 25 comb lines with a power fluctuation less than 3 dB are presented successfully. Moreover, we obtain a 10 GHz repetition rate USOPT, the pulse width of which is compressed to 2.67 ps. Our device may find its applications in the fields of ultrafast measurement, wavelength-division-multiplexing optical communication, or high-precision photonic sampling.

Self-channeling of a multi-Joule 10 µm picosecond pulse train through long distances in air.

In the long-wave infrared (LWIR) range, where, due to wavelength scaling, the critical power of Kerr self-focusing Pcr in air increases to 300-400 GW, we demonstrate that without external focusing a train of picosecond CO2 laser pulses can propagate in the form of a single several-centimeter diameter channel over hundreds of meters. The train of 10 µm pulses, for which the total energy ≥20 J is distributed over several near-terawatt picosecond pulses with a maximum power ≤2Pcr, is generated naturally during short pulse amplification in a CO2 laser. It is observed that the high-power 10 µm beam forms a large diameter "hot gas" channel in the ambient air with a ≥ 50 ms lifetime. Simulations of the experiment show that such filamentation-free self-channeling regime has low propagation losses and can deliver multi-Joule/TW-power LWIR pulses over km-scale distances.

Efficient multiphoton microscopy with picosecond pulse trains

We present an all-fiber, portable setup for multiphoton microscopy with reduced frep employing a high-energy Yb:fiber NALM laser producing 10 ps pulses. Longer pulses are less susceptible to chromatic dispersion, enhancing image brightness and contrast over conventional femtosecond pulses.

Nonlinear optical properties of both sulfonated- and halogen-substituted phenyl porphyrins with the effect of mono or bis halogen substitution and of protonation at different pH values on picosecond pulse trains generation

We studied the nonlinear dynamical propagating of picosecond pulse trains in sulfonated porphyrins. The sulfonated porphyrins were synthesized with one or two halogens (fluorine or chlorine) in phenyl rings and macrocycle protonation. One pulse train contains 25 subpulses with 70 ps width and 13.2 ns spacing. The effects of protonation at different pH values on the optical limiting behaviours of sulfonated porphyrins were also studied in this work. The energy structures of porphyrins were simplified to five-level models and Crank-Nicholson numerical method was applied to solve rate equations coupled with two-dimensional paraxial field. The results show sulfonated porphyrins are terrific optical limiters. Two halogens in phenyl rings would improve the optical limiting effects of porphyrins compared to the case of only one halogen in phenyl rings. Besides, nonprotonated sulfonated porphyrins in neutral solution with pH=7.0 show the lowest energy transmittances. But when the intensity of pulse train is strong, protonated sulfonated porphyrins in acidic solution with pH=1.4 show extremely fast growing optical limiting behaviours.

High orientation consistency and adjustable convex width of laser-induced periodic surface structures using picosecond laser pulse trains

High orientation consistency and adjustable convex width of the low-spatial-frequency laser-induced periodic surface structures (LSFLs), crucial to the functional surface characteristics, have remained elusive. This paper proposes a new method to fabricate LSFLs with high orientation consistency on the rough surface of titanium by combining laser polishing and laser induction with LSFLs with a tunable convex width via laser melting as the post-treatment. Picosecond pulses trained with a 50-ns interval are applied to regulate the thermal incubation effect and achieve laser polishing and laser nanoscale melting. The melting time of titanium for laser polishing and laser nanoscale melting is determined to be on a microsecond time scale and around 100 ns, respectively. Experimental studies show that the surface texture of titanium lowers the orientation consistency of LSFLs and that its divergence angle is 30°. Picosecond pulses with a sub-pulse number of three are applied to achieve surface polishing and the formation of the rudiment of the LSFLs, followed by the picosecond laser induction. As a result, the divergence angle of LSFLs decreases from 30° to 12°. On this basis, aiming at the problem of the narrow adjustability of the convexity ratio of LSFLs, a nanoscale melting processing method based on picosecond pulse trains with a sub-pulse number of four is proposed, and LSFLs with the tunable convexity ratios from 0.3 to 0.87 are obtained.

Influence of bovine serum albumin (BSA) on photodynamic properties of meso-tetrakis(sulfonatophenyl) porphyrin (TPPS4) for picosecond pulse trains

Due to the special interest and unique advantage of bovine serum albumin among various proteins, we carried out researches into effects of bovine serum albumin on photophysical characters of meso-tetrakis(sulfonatophenyl) porphyrin. The laser source we chose is picosecond pulse trains containing 20 subpulses of 70 picoseconds width separating by 13 nanoseconds at 532 nanometers. The theoretical analysis was carried out with a generalized five-level model representing the molecular populating structure. The two-dimensional paraxial field combined with the rate equations was solved by Crank-Nicholson numerical method. The nonlinear optical absorption mechanism in porphyrin is mainly two-step two-photon absorption. We found meso-tetrakis(sulfonatophenyl) porphyrin always shows prominent optical limiting effects binding with or without bovine serum albumin. In the presence of bovine serum albumin, the photophysical parameters of porphyrin get certain influence and cause slight weakening of optical limiting for porphyrin.

Intracavity third-harmonic generation in a continuous-wave/self-mode-locked semiconductor disk laser

The high peak power of picosecond pulses produced by a self-mode-locked semiconductor disk laser can effectively improve the efficiency of nonlinear frequency conversion. This paper presents the intracavity frequency tripling in a self-mode-locked semiconductor disk laser, and a picosecond pulse train at 327 nm wavelength is achieved. The pulse repetition rate is 0.49 GHz, and the pulse width is 5.0 ps. The obtained maximum ultraviolet output power under mode locking is 30.5 mW, and the corresponding conversion efficiency is obviously larger than that of continuous-wave operation. These ultraviolet picosecond pulses have high spatial and temporal resolution and can be applied in some emerging fields.

How Micelles Influence the Optical Limiting Properties of Zinc Porphyrins and J-Aggregates for Picosecond Pulse Trains

In this work, we studied nonlinear dynamics and optical limiting (OL) effects of pulse trains in zinc porphyrins meso-tetrakis methylpyridiniumyl (Zn2+TMPyP) and meso-tetrakis sulfonatophenyl (Zn2+TPPS) and porphyrin J-aggregates. The environments of zinc porphyrins were selected as aqueous solutions and micelles of sodium dodecyl sulfate (SDS) and cetyltrimethyl ammonium bromide (CTAB). Our numerical results show that both Zn2+TMPyP and Zn2+TPPS are good optical limiters in all solutions. Zn2+TPPS in aqueous solutions shows the best OL effect. Micelles of SDS and CTAB produced less OL effects than the aqueous solutions. The main reason lies in the first excited singlet state and intersystem crossing depending on the electronic structures in different environments.

Solvent effects on nonlinear absorption of meso-tetrakis methylpyridiniumyl porphyrin for picosecond pulse trains

Solvent effects on nonlinear absorption of meso-tetrakis methylpyridiniumyl porphyrin for picosecond pulse trains

Atom Interferometer Driven by a Picosecond Frequency Comb.

We demonstrate a light-pulse atom interferometer based on the diffraction of free-falling atoms by a picosecond frequency-comb laser. More specifically, we coherently split and recombine wave packets of cold ^{87}Rb atoms by driving stimulated Raman transitions between the |5s ^{2}S_{1/2},F=1⟩ and |5s ^{2}S_{1/2},F=2⟩ hyperfine states, using two trains of picosecond pulses in a counterpropagating geometry. We study the impact of the pulses' length as well as the interrogation time onto the contrast of the atom interferometer. Our experimental data are well reproduced by a numerical simulation based on an effective coupling that depends on the overlap between the pulses and the atomic cloud. These results pave the way for extending light-pulse interferometry to transitions in other spectral regions and therefore to other species, for new possibilities in metrology, sensing of gravito-inertial effects, and tests of fundamental physics.

Generation and dynamics of wave packets with a large phase modulation depth

This paper examines the generation of high-frequency picosecond pulse trains as a result of modulation instability of wave packets with a large phase modulation depth and small amplitude modulation depth. We demonstrate that intermediate amplification of such wave packets and subsequent phase-to-amplitude modulation conversion lead to the formation of pulses with peak powers orders of magnitude higher than their initial power. The corresponding pulse generators can be used to generate a line spectrum.

Synchronously Intracavity-Pumped Picosecond Optical Parametric Oscillators for Sensors.

The research and development of laser systems for intracavity phase interferometry is described. These systems are based on an intracavity synchronously pumped optical parametric oscillator (OPO), enabling the generation of two trains of picosecond pulses inside a single cavity. In such a configuration, it is possible to measure the beat note frequency between two pulses and to very precisely determine the phase difference between them. The pump source is a diode-pumped passively mode-locked Nd:YVO laser. A periodically poled magnesium-doped lithium niobate crystal is used as the optical parametric oscillator crystal coupling the pump and the signal cavities. We designed a synchronously pumped OPO in a linear and ring cavity configuration allowing generation in a dual-pulse regime. By a mutual detuning of both cavity lengths, the quasi-synchronous regime of pumping was achieved and high harmonics of repetition rate frequencies were generated. Such a system can be useful for applications such as pump-probe spectroscopy or for testing telecommunication systems. We also realized the subharmonic OPO cavity as a source of two independent trains of picosecond pulses suitable for intracavity phase interferometry; we also measured the beat note signal.

Supermode noise suppression with polarization-multiplexed dual-loop for active mode-locking optoelectronic oscillator.

The active mode-locking (AML) technique has been widely used in erbium-doped fiber lasers to generate picosecond pulse trains. Here we propose a novel active mode-locking dual-loop optoelectronic oscillator (AML-DL-OEO), which can generate microwave frequency comb (MFC) signals with adjustable comb spacings. Based on this scheme, the order of harmonic mode-locking is dramatically decreased for a certain AML driving frequency compared with a single-loop AML-OEO. Thus, the supermode noise caused by harmonic mode-locking can be efficiently suppressed. In addition, the sidemodes are well suppressed by the dual-loop architecture. An experiment is performed. MFC signals with different comb spacings are generated under fundamental or harmonic mode-locking states. AML-DL-OEO systems with different length differences between two loops are implemented to evaluate supermode noise suppression capability. The performance of the generated MFC signals is recorded and analyzed.

Ultrashort pulse generation from continuous-wave driven degenerate optical parametric oscillators

Degenerate <inline-formula><tex-math notation="LaTeX">$\chi ^{(2)}$</tex-math></inline-formula> optical parametric oscillators (OPOs) pumped by continuous-wave (cw) lasers in bulk or integrated format represent a promising platform for the study of classical as well as quantum phenomena, enabling interesting applications such as squeezing and random number generation. When subjected to phase modulation, such devices can generate ultrashort output pulses. In this report, we study pulse generation and spectral broadening in degenerate OPOs with intracavity electro-optic modulator (EOM). We numerically investigate ultrashort pulse generation from a cw-driven degenerate OPO based on MgO:PPLN as the nonlinear gain medium. The phase sensitive gain provided by the quadratic nonlinear medium in a detuned cavity and the inherent self-phase-locking of the degenerate field with that of the pump govern the signal amplification. Using high-performance computing tools, we study the full intracavity complex field evolution over 10000 round trips, as the OPO reaches the steady state. Taking advantage of the high nonlinear gain and low threshold of degenerate OPO, and using an intracavity EOM synchronized to the free-spectral-range of the cavity in combination with spectral filtering, we show that a stable, uniform, and periodic train of picosecond pulses of <inline-formula><tex-math notation="LaTeX">$&lt; $</tex-math></inline-formula>5 ps duration with FWHM spectral bandwidth of 0.4 THz can be generated. The results of our theoretical model are valid for <inline-formula><tex-math notation="LaTeX">$\chi ^{(2)}$</tex-math></inline-formula> OPOs in bulk and integrated format.

Different parameter influences of picosecond pulse trains on optical properties of aminophenoxy substituted phthalocyanines and covalent linkage conjugates to cadmium telluride quantum dots

We carried out the research into different parameter influences of picosecond pulse trains on optical properties of phthalocyanines with benzothiazole substitutes and the covalent attachments to cadmium telluride quantum dots (CdTe QDs). Total number of subpulses, time spacing between subpulses, width of each subpulse and propagation distance of the pulse trains were taken into account thoroughly. The covalent attachments of phthalocyanines to CdTe QDs showed more excellent optical limiting dynamics than phthalocyanines with picosecond pulse trains. Increasing the total number with broader width of subpulses is helpful to improve optical limiting properties, while the time spacing between subpulses has almost no influence.

Generation of Subpicosecond Pulse Trains in Fiber Cascades Comprising a Cylindrical Waveguide with Propagating Refractive Index Wave

A cylindrical waveguide structure with the running refractive index wave has been recently demonstrated as a means for the generation of high-repetition-rate pulse trains. The operation mechanism involves a proper combination of the frequency modulation and modulation instability simultaneously experienced by the input continuous wave (CW) signal as it propagates through the cylinder waveguide. Here, we explore the same idea but employ the cylindrical waveguide only as a part of the cascaded optical fiber configuration now comprising both passive and active optical fiber segments. The new system design enables the improved control of the pulse train formation process in the cascaded system elements, relaxes strong requirements for the CW signal power, and provides an additional optical gain for the advanced pulse peak power scaling. In particular, using a low-amplitude, weakly modulated, continuous wave as an input signal we explore and optimize the nonlinear mechanisms underlying its cascaded transformation into the train of kilowatt peak power picosecond pulses.

Polymethine dye-based optical compounds for diode pumped Nd:YAG laser systems

Polymethine dye-based optical compounds characterized by low absorption at the pump radiation wavelength 808 nm and at the same time by high absorption at the lasing wavelength 1064 nm have been developed for the diode pumped Nd:YAG laser systems. It has been theoretically shown that the thiopyrylotricarbocyanines with saturated bridging groups in the polymethine chains are the most effective medium for such applications. The passive Q-switch unit as well as the saturable absorber mirror fabricated using the developed polymethine dye-compounds were examined experimentally. It has been shown that these dye-based optical components can provide the efficient lasing in the modes of the Q-switching and formation of the picosecond pulse train.