Frequency Conversion Of Light Research Articles

Light Conversion upon Photoexcitation of NaBiF4:Yb3+/Ho3+/Ce3+ Nanocrystalline Particles.

NaBiF4 nanocrystalline particles were synthesized by means of a facile precipitation synthesis route to explore upconversion emission properties when doped with lanthanide ions. In particular, the incorporation of the Yb3+-Ho3+-Ce3+ triad with controlled ion concentration facilitates near-IR pumping conversion into visible light, with the possibility of color emission tuning depending on Ce3+ doping amount. We observed that introducing a Ce3+ content up to 20 at.% in NaBiF4:Yb3+/Ho3+, the chromaticity progressively turns from green for the Ce3+ undoped system to red. This is due to cross-relaxation mechanisms between Ho3+ and Ce3+ ions that influence the relative efficiency of the overall upconversion pathways, as discussed on the basis of a theoretical rate equation model. Furthermore, experimental results suggest that the photoexcitation of intra-4f Ho3+ transitions with light near the UV-visible edge can promote downconverted Yb3+ near-IR emission through quantum cutting triggered by Ho3+-Yb3+ energy transfer mechanisms. The present study evidences the potentiality of the developed NaBiF4 particles for applications that exploit lanthanide-based light frequency conversion and multicolor emission tuning.

Broadband frequency conversion of ultrashort pulses using high-Q metasurface resonators

Frequency conversion of light can be dramatically enhanced using high quality factor (Q-factor) resonator. Unfortunately, the achievable conversion efficiencies and conversion bandwidths are fundamentally limited by the time–bandwidth limit of the resonator, restricting their use in frequency conversion of ultrashort pulses. Here, we propose and numerically demonstrate sum-frequency generation based frequency conversion using a metasurface-based resonator configuration that could overcome this limitation. The proposed experimental configuration takes use of the spatially dispersive responses of periodic metasurfaces supporting collective surface lattice resonances (SLRs), and can be utilized for broadband frequency conversion of ultrashort pulses. We investigate a plasmonic metasurface, supporting a high-Q SLR (Q = 500, linewidth of 2 nm) centered near 1000 nm, and demonstrate ∼1000-fold enhancements of nonlinear signals. Furthermore, we demonstrate broadband frequency conversion with a pump conversion bandwidth reaching 75 nm, a value that greatly surpasses the linewidth of the studied resonator. Our work opens new avenues to utilize high-Q metasurfaces for broadband nonlinear frequency conversion.

Geometric phase opens new frontiers in nonlinear frequency conversion of light

Geometric phase opens new frontiers in nonlinear frequency conversion of light

Second harmonic generation in periodically poled MgO:LN crystal with 2 µm period created by e-beam irradiation

The periodical domain structure with period 2 μm was created in 1-mm-thick MgO doped lithium niobate single crystals by electron-beam irradiation. The second harmonic generation (SHG) around 370 nm was obtained during pumping the crystals by 100 mW continuous wave tunable Ti:Sapphire laser. The normalized efficiency was 0.05%/W. The dependence of the SHG power on the pump beam position has indicated that the periodical domain structure depth is about 300 μm. The obtained results have demonstrated that the electron-beam poling can be used for creation of the short pitch periodical domain structures for light frequency conversion.

Photon Pairs from Resonant Metasurfaces.

All-dielectric optical metasurfaces are a workhorse in nano-optics, because of both their ability to manipulate light in different degrees of freedom and their excellent performance at light frequency conversion. Here, we demonstrate first-time generation of photon pairs via spontaneous parametric-down conversion in lithium niobate quantum optical metasurfaces with electric and magnetic Mie-like resonances at various wavelengths. By engineering the quantum optical metasurface, we tailor the photon-pair spectrum in a controlled way. Within a narrow bandwidth around the resonance, the rate of pair production is enhanced up to 2 orders of magnitude, compared to an unpatterned film of the same thickness and material. These results enable flat-optics sources of entangled photons—a new promising platform for quantum optics experiments.

Optical frequency conversion of light with maintaining polarization and orbital angular momentum.

Optical frequency conversion provides a fundamental and important approach to manipulate light in frequency domain. In such a process, manipulating the frequency of light without changing information in other degrees of freedom of light will enable us to establish an interface between various optical systems operating in different frequency regions and have many classical and quantum applications. Here we experimentally demonstrate a frequency conversion with maintaining polarization and orbital angular momentum (OAM) by successfully upconverting various polarization-OAM composite states in a nonlinear Sagnac interferometer. Our scheme offers a new possibility for building different wave band interfaces in more degrees of freedom.

Real-Time Imaging of Short-Wave Infrared Luminescence Lifetimes for Anti-counterfeiting Applications.

Rare-earth doped nanoparticles (RENPs) have been widely used for anti-counterfeiting and security applications due to their light frequency conversion features: they are excited at one wavelength, and they display spectrally narrow and distinguished luminescence peaks either at shorter wavelengths (i.e., frequency/energy upconversion) or at longer wavelengths (frequency/energy downconversion). RENPs with a downconversion (DC) photoluminescence (PL) in short-wave infrared (SWIR) spectral range (~1,000–1,700 nm) have recently been introduced to anti-counterfeiting applications, allowing for multilevel protection based on PL imaging through opaque layers, due to a lesser scattering of SWIR PL emission. However, as the number and spectral positions of the discrete PL bands exhibited by rare-earth ions are well-known, it is feasible to replicate luminescence spectra from RENPs, which results in a limited anti-counterfeiting security. Alternatively, lifetime of PL from RENPs can be used for encoding, as it can be finely tuned in broad temporal range (i.e., from microseconds to milliseconds) by varying type of dopants and their content in RENPs, along with the nanoparticle morphology and size. Nevertheless, the current approach to decoding and imaging the RENP luminescence lifetimes requires multiple steps and is highly time-consuming, precluding practical applications of PL lifetime encoding for anti-counterfeiting. Herein, we report the use of a rapid lifetime determination (RLD) technique to overcome this issue and introduce real-time imaging of SWIR PL lifetime for anti-counterfeiting applications. NaYF4:20% Yb, x% Er (x = 0, 2, 20, 80)@NaYF4 core@shell RENPs were synthesized and characterized, revealing DC PL in SWIR region, with maximum at ~1,530 nm and PL lifetimes ranging from 3.2 to 6 ms. Imaging of the nanoparticles with different lifetimes was performed by the developed time-gated imaging system engaging RLD method and the precise manipulation of the delay between the excitation pulses and camera gating windows. Moreover, it is shown that imaging and decrypting can be performed at a high rate (3–4 fps) in a cyclic manner, thus allowing for real-time temporal decoding. We believe that the demonstrated RLD-based fast PL lifetime imaging approach can be employed in other applications of photoluminescent RENPs.

Frequency Conversion in a Time-Variant Dielectric Metasurface.

The color of light is a fundamental property of electromagnetic radiation; as such, control of the frequency is a cornerstone of modern optics. Nonlinear materials are typically used to generate new frequencies, however the use of time-variant systems provides an alternative approach. Utilizing a metasurface that supports a high-quality factor resonance, we demonstrate that a rapidly shifting refractive index will induce frequency conversion of light that is confined in the nanoresonator meta-atoms. We experimentally observe this frequency conversion and develop a time-dependent coupled mode theory model that well describes the system. The intersection of high quality-factor resonances, active materials, and ultrafast transient spectroscopy leads to the demonstration of metasurfaces operating in a time-variant regime that enables enhanced control over light-matter interaction.

Nonlinear frequency conversion of light inside a microcavity

Changing the color of light in a small mode volume is essential for applications that require on-chip operation. Microcavities are profound structures given their property to confine light in a small mode volume. Here, I numerically investigate the frequency conversion of light in a microcavity and show that the frequency converted light intensity is distinguished from an open medium such as an optical fiber or a nonlinear crystal. I observe that the frequency converted light intensity increases with increased rate of change of the refractive index of the microcavity. Notably, this study shows that the intensity of the frequency converted light is maximized when the duration of the index perturbation is matched to the cavity storage time. The results provide a set of optimum parameters for increasing frequency conversion efficiency inside a microcavity.

Dewetting mechanisms and their exploitation for the large-scale fabrication of advanced nanophotonic systems

ABSTRACTRecent progress in submicron- and nano-fabrication technologies has led to the emergence of novel photonic structures such as optical nanoantennas and metasurfaces. Real-life applications of these advanced photonic structures still require substantial improvement of the fabrication processes, in terms of their throughput and cost-effectiveness. Because of its simplicity and effectiveness, dewetting of a thin film has attained increasing attention as a feasible process for improving the scalability and productivity. Here, we provide an overview of the mechanisms and phenomenologies of dewetting to foster an improved fundamental understanding necessary for the optimisation of the dewetting process condition and template design. We then review the strategies demonstrating the use of templated-dewetting for producing well-aligned arrays of submicron- and nanostructures with great control over their size, shape and arrangement. Recent applications of dewetted structures in advanced nanophotonics are reviewed with an emphasis on the exploitation of dewetting mechanisms. Special attention is given to the fabrication of resonant optical nanoantennas and nanophotonic applications in which high repeatability and throughput are important parameters: sensing, colourisation, photovoltaics and nonlinear light frequency conversion. We expect this review to provide a basis for the use of thin-film dewetting to realise the industrial-level fabrication of various practical advanced photonic systems.

Synthesis and characterization of titanium nitride thin films for enhancement and localization of optical fields

Emerging plasmonic materials are an essential driving factor of the ongoing progress towards the empowering of photonic devices functionalities and performance improvement. Transition metal nitrides, being refractory metals with tunable optical properties, are prominent representatives of alternative plasmonic materials. Recent intensive examination of linear and nonlinear optical parameters of metal nitrides has revealed TiN to be a promising media for metal-based optics. Another distinctive feature of TiN is its Raman activity. In contrast to Raman-silent metals, TiN-based structures enable nonlinear light frequency conversion not only to even and odd harmonics, but also to Raman-shifted modes. Moreover, the threshold of the underlying stimulated Raman scattering (SRS) effect in these structures could be greatly reduced by appropriate geometry and material design. Here we experimentally investigate the effect of structure and composition of TiN on its optical properties, such as dielectric permittivity and third-order Raman susceptibility. A special attention is given to synthesis and characterization of TiN thin films suitable for plasmon-assisted localization and amplification of optical signals.

An Anthracene-Incorporated [8]Cycloparaphenylene Derivative as an Emitter in Photon Upconversion.

The anthracene-incorporated [8]cycloparaphenylene 2 has been synthesized and its optoelectronic properties studied by UV-vis spectroscopy, cyclic voltammetry, and DFT calculations. NMR and computational studies indicate that the new cycloparaphenylene derivative possesses a Cs point group symmetry. The new CPP 2 exhibits peculiar optoelectronic properties: (i) fluorescence emission is blue-shifted with respect to [8]cycloparaphenylene 1, and its quantum yield is higher; (ii) in the presence of an octaethylporphyrin Pd complex, as sensitizer, it undergoes a visible light upconversion. This is the first case in which a cycloparaphenylene derivative is involved as an emitter in low power light frequency conversion.

Full 3D modelling of pulse propagation enables efficient nonlinear frequency conversion with low energy laser pulses in a single-element tripler

Although new optical materials continue to open up access to more and more wavelength bands where femtosecond laser pulses can be generated, light frequency conversion techniques are still indispensable in filling the gaps on the ultrafast spectral scale. With high repetition rate, low pulse energy laser sources (oscillators) tight focusing is necessary for a robust wave mixing and the efficiency of broadband nonlinear conversion is limited by diffraction as well as spatial and temporal walk-off. Here we demonstrate a miniature third harmonic generator (tripler) with conversion efficiency exceeding 30%, producing 246 fs UV pulses via cascaded second order processes within a single laser beam focus. Designing this highly efficient and ultra compact frequency converter was made possible by full 3-dimentional modelling of propagation of tightly focused, broadband light fields in nonlinear and birefringent media.

Single-photon frequency conversion via interaction with a three-level atom coupled to a microdisk

The frequency conversion of light has proved to be an important instrument for communication, spectroscopy, imaging and information processing. We theoretically study the frequency conversion of a single photon via its interaction with a -type atom coupled to a microdisk. We show that the frequency conversion efficiency approaches unity even in the case of an interaction between clockwise and counterclockwise modes in the microdisk due to surface imperfections. By the use of the Schrieffer–Wolff transformation, we get an effective Hamiltonian that allows us to investigate the dynamics of the system and obtain time and probability of frequency conversion in different conditions.

Nonlinear Surface Magnetoplasmonics in Kretschmann Multilayers

The nonlinear magneto-plasmonics aims to utilize plasmonic excitations to control the mechanisms and taylor the efficiencies of the non-linear light frequency conversion at the nanoscale. We investigate the mechanisms of magnetic second harmonic generation in hybrid gold-cobalt-silver multilayer structures, which support propagating surface plasmon polaritons at both fundamental and second harmonic frequencies. Using magneto-optical spectroscopy in Kretschmann geometry, we show that the huge magneto-optical modulation of the second harmonic intensity is dominated by the excitation of surface plasmon polaritons at the second harmonic frequency, as shown by tuning the optical wavelength over the spectral region of strong plasmonic dispersion. Our proof-of-principle experiment highlights bright prospects of nonlinear magneto-plasmonics and contributes to the general understanding of the nonlinear optics of magnetic surfaces and interfaces.

Micro- and nano-domain engineering in lithium niobate

The physical basis of the domain engineering in ferroelectrics and its application to lithium niobate crystals were reviewed. The unified kinetic approach to the domain structure evolution in electric field was formulated and its validity for understanding the variety of observed domain evolution scenarios was demonstrated. The kinetics and statics of the domain structure in the crystals of lithium niobate family including congruent, stoichiometric, and MgO doped ones have been discussed. The main stages of the periodical poling process and related problems have been pointed out. The basic poling techniques applied for creation of the periodical domain structures in bulk crystals and waveguides were compared. The recent applications of the periodically poled lithium niobate for light frequency conversion using second harmonic generation and optical parametric oscillation, excitation of the surface acoustic waves, and generation of terahertz radiation have been discussed. The special attention has been paid for achievements in fabrication of high-power optical parametric oscillation and integrated optical devices with periodically poled lithium niobate. The future trends in periodical poling and development of the nanodomain engineering which will allow to create the nanoscale domain patterns necessary for utilization of the new nonlinear interactions were reviewed.

Domain patterning by electron beam of MgO doped lithium niobate covered by resist

Periodical domain structuring by focused electron beam irradiation of MgO-doped lithium niobate (MgOCLN) single crystalline plate covered by resist layer was studied both experimentally and by computer simulation. The dependences of domain size on the charge dose and distance between isolated domains were measured. It has been shown that the quality of periodical domain pattern depends on the thickness of resist layer and electron energy. The experimentally obtained periodic domain structures have been divided into four types. The irradiation parameters for the most uniform patterning were obtained experimentally. It was shown by computer simulation that the space charge slightly touching the crystal surface produced the maximum value of electric field at the resist/LN interface thus resulting in the best pattern quality. The obtained knowledge allowed us to optimize the poling process and to make the periodical domain patterns in 1-mm-thick wafers with an area up to 1 × 5 mm2 and a period of 6.89 μm for green light second harmonic generation. Spatial distribution of the efficiency of light frequency conversion confirmed the high homogeneity of the tailored domain patterns.

Orbital angular momentum light frequency conversion and interference with quasi-phase matching crystals

Light with helical phase structures, carrying quantized orbital angular momentum (OAM), has many applications in both classical and quantum optics, such as high-capacity optical communications and quantum information processing. Frequency conversion is a basic technique to expand the frequency range of the fundamental light. The frequency conversion of OAM-carrying light gives rise to new physics and applications such as up-conversion detection of images and generation of high dimensional OAM entanglements. Quasi-phase matching (QPM) nonlinear crystals are good candidates for frequency conversion, particularly due to their high-valued effective nonlinear coefficients and no walk-off effect. Here we report the first experimental second-harmonic generation (SHG) of an OAM-carried light with a QPM crystal, where a UV light with OAM of 100 ℏ is generated. OAM conservation is verified using a specially designed interferometer. With a pump beam carrying an OAM superposition of opposite sign, we observe interesting interference phenomena in the SHG light; specifically, a photonics gear-like structure is obtained that gives direct evidence of OAM conservation, which will be very useful for ultra-sensitive angular measurements. Besides, we also develop a theory to reveal the underlying physics of the phenomena. The methods and theoretical analysis shown here are also applicable to other frequency conversion processes, such as sum frequency generation and difference-frequency generation, and may also be generalized to the quantum regime for single photons.

Ultrafast modulation of polarization amplitude by terahertz fields in electronic-type organic ferroelectrics

Ferroelectrics sometimes show large electro-optical and non-linear optical effects, available for polarization rotation and frequency conversion of light, respectively. If the amplitude of ferroelectric polarization is modulated in the picosecond time domain, terahertz repetition of optical switching via electro-optical and non-linear optical effects would be achieved. Here we show that polarization amplitude can be rapidly modulated by a terahertz electric field in an organic ferroelectric, tetrathiafulvalene-p-chloranil (TTF-CA). In this compound, alternately stacked donor (TTF) and acceptor (CA) molecules are dimerized via the spin-Peierls mechanism, and charge transfer within each dimer results in a new type of ferroelectricity called electronic-type ferroelectricity. Using a terahertz field, the intradimer charge transfer is strongly modulated, producing a subpicosecond change in the macroscopic polarization, which is demonstrated by transient reflectivity and second-harmonic generation measurements. Subsequently, coherent oscillation of the dimeric molecular displacements occur, which is explained by the modulation of the spin moment of each molecule.

Domain Nanotechnology in Ferroelectric Single Crystals: Lithium Niobate and Lithium Tantalate Family

The recent achievements in domain nanotechnology in single crystals of lithium niobate and lithium tantalate family have been reviewed. The formation of nanoscale domain structures has been studied with high spatial resolution using modern experimental methods of domain visualization. Criteria of the investigated ferroelectric material selection and recent experimental achievements have been presented. The physical basis of the nanodomain engineering based on the role of nanoscale domains in formation of the domain patterns in highly non-equilibrium switching conditions has been discussed. The obtained knowledge allows us to manufacture the highly efficient periodically poled crystals for laser light frequency conversion.