Observation of Replica Symmetry Breaking in Standard Mode-Locked Fiber Laser.

We report the first experimental demonstration of the replica symmetry breaking (RSB) phenomenon in a fiber laser system supporting standard mode-locking (SML) regime. Though theoretically predicted, this photonic glassy phase remained experimentally undisclosed so far. We employ an ytterbium-based mode-locked fiber laser with a very rich phase diagram. Two phase transitions are observed separating three different regimes: cw, quasi-mode-locking (QML), and SML. The regimes are intrinsically related to the distinct dynamics of intensity fluctuations in the laser spectra. We set the connection between the RSB glassy phase with frustrated modes and onset of L-shaped intensity distributions in the QML regime, which impact directly the replica overlap measure.

Near-infrared ultrafast third-order nonlinear optical response of 2D NbS2, NbSe2, ZrTe2, and MoS2.

By employing the optical Kerr gate technique at 800 nm with 180 fs pulses at 76 MHz, we evaluated the third-order nonlinear optical response of two-dimensional (2D) semiconducting MoS2, semimetallic ZrTe2, and metallic NbS2 and NbSe2. The modulus of the nonlinear refractive index was measured to range from 8.6 × 10-19 m2/W to 5.3 × 10-18 m2/W, with all materials' response time limited by the pulse duration. The physical mechanism to explain the ultrafast response time's origin considers the nature of the 2D material, as will be discussed.

Latin America Optics and Photonics 2022: introduction to the feature issue.

The 2022 Latin America Optics and Photonics Conference (LAOP 2022), the major international conference sponsored by Optica in Latin America, returned to Recife, Pernambuco, Brazil, after its first edition in 2010. Held every two years since (except for 2020), LAOP has the explicit objective to promote Latin American excellence in optics and photonics research and support the regional community. In the 6th edition in 2022, it featured a comprehensive technical program with recognized experts in fields critical to Latin America, highly multidisciplinary, with themes from biophotonics to 2D materials. The 191 attendees of LAOP 2022 listened to five plenary speakers, 28 keynotes, 24 invited talks, and 128 presentations, including oral and posters.

Distributed vibration sensor with a lasing phase-sensitive OTDR.

The authors experimentally demonstrate the operation of a lasing phase-sensitive optical time-domain reflectometer (Φ-OTDR) based on random feedback from a sensing fiber. Here, the full output of the laser provides the sensing signal, in contrast to the small backscattered signal measured in a conventional OTDR. In this proof-of-principle demonstration, the laser operates as a distributed vibration sensor with signal-to-noise ratio of 23-dB and 1.37-m spatial resolution.

Evaluation of Pearson correlation coefficient and Parisi parameter of replica symmetry breaking in a hybrid electronically addressable random fiber laser.

The hybrid electronically addressable random (HEAR) laser is a novel type of random fiber laser that presents the remarkable property of selection of the fiber section with lasing emission. Here we present a joint analysis of the correlations between intensity fluctuations at distinct wavelengths and replica symmetry breaking (RSB) behavior of the HEAR laser. We introduce a modified Pearson coefficient that simultaneously comprises both the Parisi overlap parameter and standard Pearson correlation coefficient. Our results highlight the contrast between the correlations and presence or not of RSB phenomenon in the spontaneous emission behavior well below threshold, replica-symmetric ASE regime slightly below threshold, and RSB phase with random lasing emission above threshold. In particular, in the latter we find that the onset of RSB behavior is accompanied by a stochastic dynamics of the lasing modes, leading to competition for gain intertwined with correlation and anti-correlation between modes in this complex photonic phase.

Fifth-order optical nonlinear response of semiconducting 2D LTMD MoS2.

The effective fifth-order susceptibility, ${\chi}_{\rm eff}^{(5)}$, of two-dimensional (2D) semiconducting layered transition metal dichalcogenide (LTMD) molybdenum disulfide (${\rm MoS}_2$) is reported here for the first time, to the best of our knowledge. Using the $ Z $-scan technique with a laser operating at 800 nm, 1 kHz, 100 fs, we investigated the nonlinear behavior of ${\rm MoS}_2$ suspended in acetonitrile (concentration, 70 µg/ml). The effective nonlinear refractive index ${{n}_{4,{eff}}} = - ({7.6 \pm 0.5}) \times {10^{- 26}}\; {{\rm cm}^4}/{{\rm W}^2}$, proportional to ${\rm Re}{\chi}_{\rm eff}^{(5)}$, was measured for monolayer ${\rm MoS}_2$ nanoflakes, prepared by a modified redox exfoliation method. We also determined the value of the nonlinear refractive index ${{n}_2} = + ({4.8 \pm 0.5}) \times {10^{- 16}}\;{{\rm cm}^2}/{\rm W}$, which is related to the material's effective third-order optical susceptibility real part, ${Re\chi}_{\rm eff}^{(3)}$. For comparison, we also investigated the nonlinear response of tungsten disulfide (${\rm WS}_2$) monolayers, prepared by the same method and suspended in acetonitrile (concentration, 40 µg/ml), which only exhibited the third-order nonlinear effect in the same intensity range, up to ${120}\;{{{\rm GW}/{\rm cm}}^2}$. Nonlinear absorption was not observed in either ${\rm MoS}_2$ or ${\rm WS}_2$.

Hybrid electronically addressable random fiber laser.

We report here a novel architecture for a random fiber laser exploiting the combination of a semiconductor optical amplifier (SOA) and an erbium doped fiber (EDF). The EDF was optically biased by a continuous wave pump laser, whereas the SOA was arranged in a fiber loop-mirror and driven by nanosecond duration current pulses. Laser pulses were obtained by synchronizing the SOA driver to the returning amplified Rayleigh back-scattered light from a selected short section of the EDF. By tuning the SOA pulse rate, random lasing was achieved by addressing selected meter-long sections of the 81-m long EDF, which was open-ended. Laser oscillation can be potentially obtained with SOA modulation frequencies from several kHz to the MHz regime. We discuss the mechanism leading to the hybrid random laser emission, connecting with phase sensitive optical time domain reflectometry and envision potential applications of this electronically addressable random laser.

Ultrafast convergent power-balance model for Raman random fiber laser with half-open cavity.

The power-relevant features of Raman random fiber laser (RRFL), such as lasing threshold, slope efficiency, and power distribution, are among the most critical parameters to characterize its operation status. In this work, focusing on the power features of the half-open cavity RRFL, an ultrafast convergent power-balance model is proposed, which highlights the physical essence of the most common RRFL type and sharply reduces the computation workload. By transforming the time-consuming serial calculation to a parallel one, the calculation efficiency can be improved by more than 100 times. Particularly, for different point-mirror reflectivities and different fiber lengths, the input-output power curves and power distribution curves calculated by the present model match nicely with those of the conventional model, as well as with the experimental data. Moreover, through the present model the relationship between point-mirror reflectivity and laser threshold is analytically derived, and the way for improving RRFL's slope efficiency is also provided with a lucid theoretical explanation.

Nonlinear photoacoustic response of suspensions of laser-synthesized plasmonic titanium nitride nanoparticles.

A nonlinear photoacoustic (PA) response from solutions of 40 nm plasmonic titanium nitride nanoparticles (NPs) synthesized by laser ablation in a liquid environment (acetone) is reported. Using a photoacoustic Z-scan with 5 ns pumping pulses, values of effective nonlinear absorption (NLA) coefficients ßPA,eff were measured and found to be 3.27±0.17 × 10-8, 6.41±0.32 × 10-8, and 3.22±0.16 × 10-8 for 600, 700, and 800 nm pumping wavelengths, respectively. To take into account the influence of nonlinear scattering, absorption-dependent PA measurements were carried out together with the optical Z-scan, and the obtained data were compared. The origin of the effective absorptive nonlinearity is discussed based on combined NLA in NPs, nonlinear scattering, and bubble generation triggered by NP-mediated light absorption. Potential applications include biomedical diagnostics and therapy.

Hyper-Rayleigh scattering in 2D redox exfoliated semi-metallic ZrTe2 transition metal dichalcogenide.

Nonlinear optical characterization of nanostructured layered transition metal dichalcogenides (LTMDs) is of fundamental interest for basic knowledge and applied purposes. In particular, second-order optical nonlinearities are the basis for second harmonic generation as well as sum or difference frequency generation and have been studied in some 2D TMDs, especially in those with a semiconducting character. Here we report, for the first time, on the second-order nonlinearity of the semi-metallic ZrTe2 monolayer in acetonitrile suspension (concentration of 4.9 × 1010 particles per cm3), synthesized via a modified redox exfoliation method and characterized using the Hyper-Rayleigh scattering technique in the nanosecond regime. The orientation-averaged first-hyperpolarizability was found to be ß(2ω) = (7.0 ± 0.3) × 10-24 esu per ZrTe2 monolayer flake, the largest reported so far. Polarization-resolved measurements were performed in the monolayer suspension and indicate the dipolar origin of the generated incoherent second harmonic wave.

Nonlinear effects and photonic phase transitions in Nd3+-doped nanocrystal-based random lasers.

The interplay between gain and scattering of light propagating in disordered media allows operation of random lasers (RLs)-lasers without conventional optical cavities. In the present paper, we review our recent contributions in this area, which include the demonstration of self-second-harmonic and self-sum-frequency generation, the characterization of Lévy's statistics of the output intensity fluctuations, and replica symmetry breaking (analogue to the spin-glass phase transition) by RLs based on nanocrystals containing trivalent neodymium ions.

Evidence of a Floquet Phase in a Photonic System.

The ground breaking extension of the key concept of phase structure to nonequilibrium regimes was only recently achieved in Floquet systems, characterized by a time-dependent quantum Hamiltonian with a periodic driving source. However, despite the theoretical advances, only very few systems are known to display experimental Floquet phases, not one of them employing a laser emission-based mechanism. Here we report the first experimental observation of a Floquet phase in a photonic system, a disordered fiber laser with spatial eigenmode localization. We apply a periodically oscillating cw pumping source that drives the random couplings of the Floquet Hamiltonian. A photonic Floquet spin-glass phase is demonstrated in the random-lasing regime by extensive measurements of the Parisi overlap parameter and asymmetry properties of its distribution. In contrast, in the fluorescent regime below threshold, the absence of mode localization prevents the stabilization of a Floquet phase. Our results are nicely described by theoretical arguments.

Linear and nonlinear optical characterization of self-assembled, large-area gold nanosphere metasurfaces with sub-nanometer gaps: errata.

We correct a nomenclature error for the plasmon ruler equation used to fit the simulation data in Fig. 2(d) [Opt. Express24, 27360 (2016)].

Nonlinear refractive index of electric field aligned gold nanorods suspended in index matching oil measured with a Hartmann-Shack wavefront aberrometer.

The capability to dynamically control the nonlinear refractive index of plasmonic suspensions may enable innovative nonlinear sensing and signaling nanotechnologies. Here, we experimentally determine the effective nonlinear refractive index for gold nanorods suspended in an index matching oil aligned using electric fields, demonstrating an approach to modulate the nonlinear optical properties of the suspension. The nonlinear optical experiments were carried out using a Hartmann-Shack wavefront aberrometer in a collimated beam configuration with a high repetition rate femtosecond laser. The suspensions were probed at 800 nm, overlapping with the long-axis absorption peak of the nanorods. We find that the effective nonlinear refractive index of the gold nanorods suspension depends linearly on the orientational order parameter, S, which can be understood by a thermally induced nonlinear response. We also show the magnitude of the nonlinear response can be varied by ∼ 60%.

Replica Symmetry Breaking in the Photonic Ferromagneticlike Spontaneous Mode-Locking Phase of a Multimode Nd:YAG Laser.

We demonstrate the replica symmetry breaking (RSB) phenomenon in the spontaneous mode-locking regime of a multimode Q-switched Nd:YAG laser. The underlying mechanism is quite distinct from that of the RSB recently observed in random lasers. Here, there is no random medium and the phase is not glassy with incoherently oscillating modes as in random lasers. Instead, in each pulse a specific subset of longitudinal modes are activated in a nondeterministic way, whose coherent oscillation dominates and frustrates the others. The emergence of RSB coincides with the onset of ultrashort pulse generation typical of the spontaneous mode-locking regime, both occurring at the laser threshold. On the other hand, when high losses are introduced, RSB is inhibited and only the amplified stimulated emission with replica symmetry is observed. Our results disclose the only theoretically predicted photonic phase with RSB that remained unobserved so far.

Techniques for nonlinear optical characterization of materials: a review.

Various techniques to characterize the nonlinear (NL) optical response of centro-symmetric materials are presented and evaluated with emphasis on the relationship between the macroscopic measurable quantities and the microscopic properties of photonic materials. NL refraction and NL absorption of the materials are the phenomena of major interest. The dependence of the NL refraction and NL absorption coefficients on the nature of the materials was studied as well as on the laser excitation characteristics of wavelength, intensity, spatial profile, pulse duration and pulses repetition rate. Selected experimental results are discussed and illustrated. The various techniques currently available were compared and their relative advantages and drawbacks were evaluated. Critical comparisons among established techniques provided elements to evaluate their accuracies and sensitivities with respect to novel methods that present improvements with respect to the conventional techniques.

Linear and nonlinear optical characterization of self-assembled, large-area gold nanosphere metasurfaces with sub-nanometer gaps.

We created centimeter-scale area metasurfaces consisting of a quasi-hexagonally close packed monolayer of gold nanospheres capped with alkanethiol ligands on glass substrates using a directed self-assembly approach. We experimentally characterized the morphology and the linear and nonlinear optical properties of metasurfaces. We show these metasurfaces, with interparticle gaps of 0.6 nm, are modeled well using a classical (without charge transfer) description. We find a large dispersion of linear refractive index, ranging from values less than vacuum, 0.87 at 600 nm, to Germanium-like values of 4.1 at 880 nm, determined using spectroscopic ellipsometry. Nonlinear optical characterization was carried out using femtosecond Z-scan and we observe saturation behavior of the nonlinear absorption (NLA) and nonlinear refraction (NLR). We find a negative NLR from these metasurfaces two orders of magnitude larger (n2,sat = -7.94x10-9 cm2/W at Isat,n2 = 0.43 GW/cm2) than previous reports on gold nanostructures at similar femtosecond time scales. We also find the magnitude of the NLA comparable to the largest values reported (ß2,sat = -0.90x105 cm/GW at Isat,ß2 = 0.34 GW/cm2). Precise knowledge of the index of refraction is of crucial importance for emerging dispersion engineering technologies. Furthermore, utilizing this directed self-assembly approach enables the nanometer scale resolution required to develop the unique optical response and simultaneously provides high-throughput for potential device realization.

Observation of photonic paramagnetic to spin-glass transition in a specially designed TiO2 particle-based dye-colloidal random laser.

Colloidal-based random lasers (RLs) are highly efficient and have been exploited in a wide range of geometries. However, in the particular case of ethanol solutions of rhodamines and TiO2 particles, the RL behavior is quite unstable due to the fast precipitation of the particles. In this Letter, specially designed amorphous TiO2 particles were synthesized by a sol-gel method, preventing the degradation of the RL for long operating lifetimes of over 105 shots. As a consequence, this modified colloidal RL allowed the observation of a clear replica-symmetry-breaking phase transition from the paramagnetic fluorescent to spin-glass RL behavior, which has not been observed in the system with nonfunctionalized TiO2 particles.

A founder mutation in the TCIRG1 gene causes osteopetrosis in the Ashkenazi Jewish population.

Osteopetrosis is a rare and heterogeneous genetic disorder characterized by dense bone mass that is a consequence of defective osteoclast function and/or development. Autosomal recessive osteopetrosis (ARO) is the most severe form and is often fatal within the first years of life; early hematopoietic stem cell transplant (HSCT) remains the only curative treatment for ARO. The majority of the ARO-causing mutations are located in the TCIRG1 gene. We report here the identification and characterization of an A to T transversion in the fourth base of the intron 2 donor splice site (c.117+4A→T) in TCIRG1, a mutation not previously seen in the Ashkenazi Jewish (AJ) population. Analysis of a random sample of individuals of AJ descent revealed a carrier frequency of approximately 1 in 350. Genotyping of five loci adjacent to the c.117+4A→T-containing TCIRG1 allele revealed that the presence of this mutation in the AJ population is due to a single founder. The identification of this mutation will enable population carrier testing and will facilitate the identification and treatment of individuals homozygous for this mutation.

Direct three-photon excitation of upconversion random laser emission in a weakly scattering organic colloidal system.

We report the operation and characterization of an upconversion random laser emitting at 560 nm, when directly pumped by three photon excitation at the near IR wavelength of 1350 nm in a colloidal dye solution in the weakly scattering regime. Using a special dye with a high three-photon cross-section and TiO(2) nanoparticles (250 nm diameter), optimized upconverted emission was obtained for particle densities of ~2 x 10(9)/cm3. A strong dependence on the nanoparticle concentration and the pumping area was verified. The presence of spikes with linewidths ~0.4 nm in the emitted spectrum is the signature of coherent emission from this three-photon pumped random laser.