Narrow Results

The aspherical lens is an optical element used to effectively reduce optical aberration, a consequence of reducing the number of spherical surfaces in the complex optical system. In this paper, we suggest that a nonlinear lens formed in the Kerr medium irradiated by the laser Gaussian beam will be the aspherical lens. The expression describing the transverse distribution of index inside Kerr medium concerns the nonlinear coefficient of refractive index, and the laser intensity is derived approximately limited to the fourth-order term of the Maclaurins formula for Gaussian function. Based on the paraxial approximation, the expression of surface profile (sag) and the spherical aberration of the nonlinear aspherical lens are introduced and used for the numerical simulation of the model of the organic dye thin layer irradiated by laser Gaussian beam. The obtained results confirm the aspherical surface of the nonlinear aspherical lens and the spherical aberration has very low visible wavelength. The capability to reduce and neglect the spherical aberration when using the nonlinear lens as an aspherical surface in a complex optical system or a nonlinear lens for optical tweezers is discussed.

This work aims to discuss the impact of the interaction of a high-power laser with the SrWO₄/MoS₂ nanocomposites synthesized by the solvothermal method. The effect of different concentrations of MoS₂ on the structural, morphological, optical and nonlinear optical (NLO) characteristics of SrWO₄ nanostructures was studied by utilizing XRD, Raman, FTIR, SEM, TEM, UV–Visible absorption and Open aperture Z-scan technique using Nd: YAG pulsed laser. The composites mitigate the successful interaction of MoS₂ in the SrWO₄ lattice through standard phase confirmation, change in lattice parameters and induced strain from XRD analysis. The mixed morphology shows the blended nature of composites through HRTEM and SEM. The functional and vibrational modes of nanocomposites were explored by FTIR and Raman spectroscopic techniques. The photoluminescence spectroscopy analyzed the influence of defect states. The optical parameters like absorption edge, band gap energy and Urbach energy were calculated by linear optical studies. Z-scan studies show the reverse saturable nature of all samples with more absorption and less transmittance at the focus. The experiment was extended to the analysis of the optical limiting (OL) behavior studies to understand their potential application in laser safety devices. The higher concentration of MoS₂ in the strontium matrix yields a higher nonlinear absorption coefficient of $1.531\times 10^{-10}$m/W and a lower optical threshold of $0.61\times 10^{11}$W/m². The inclusion of 20% MoS₂ in SrWO₄ significantly enhances the nonlinear absorption and the optical limiting ability which can be the best choice of NLO material for future optoelectronics.

This work studies the development of windows of harmonious instability in negative refractive material. After taking into account the fundamental need to monitor instability, such as self-phase modulation and group velocity spreading, we first examine the effects on the gain spectrum of fourth and third-order dispersals, cubic–quintic nonlinearity, higher-order nonlinear dispersions, self-steepening, and detuning parameter. Furthermore, in metamaterials with the aforementioned nonlinear effects, we investigate the influence of an adjustable nonlinear saturation effect over the modulational instability. Tunable modulation instability (MI) gain spectrum formation results from the tunable material parameters made possible by the engineering freedom offered by metamaterials. As a structure is operated at high incident power, generally exceeding the medium’s saturation inception, the SNL becomes a robust case. The nonlinear saturation window with negative index material can also produce adjustable instability gain spectrum formation. More methods for forming solitons and ultrashort pulses with desired parameters can be achieved with this tunable gain spectrum. The numerical approach validates the analytical prediction that came from the linear stability study.

This study investigates the photoresponsive behavior of substituted azobenzenes with a specific focus on their nonlinear optical response. This study suggests that azoimidazole substitution is a better alternative to azobenzene derivatives for nonlinear optical responses. The synthesis, characterization, photophysical property and isomerization pathway of 2-[(E)-(4-fluorophenyl)diazenyl]-1H-imidazole (E-2g) are presented as an optical limiter through a comprehensive blend of experimental and theoretical approaches. Notably, E-2g exhibited a lower energy barrier than reported azobenzenes. The trans-to-cis photostationary state was reached in 75 min, while the cis-to-trans state was achieved in 60 min at 354 nm. The study further explores the photoisomerization pathway of E-2g, highlighting its nonlinear absorption, which has a nonlinear absorption coefficient (${\beta }_{\mathrm{\text{eff}}}$) of 8.8 × 10^–11 m/W at 20 $\mu$J, as determined by Z-scan measurements. The results suggest that E-2g exhibits significant nonlinear absorption characteristics, which helps in applications requiring protection from intense light sources.

In 2003, we demonstrated a non-destructive terahertz spectroscopic imaging of illicit drugs hidden in envelopes using a widely tunable THz-wave parametric source, though its dynamic range at that time was less than four orders. Recently, we have realized more than nine orders of dynamic range with an evolved injection seeded THz-wave spectrometer. Now we can detect drugs under much thicker obstacles than before. In this report, we introduce the result of THz spectroscopic imaging of chemicals under thick envelopes and related topics; Enhanced tuning range of is-TPG up to 5 THz and >90 dB dynamic range THz spectroscopic system.

Thin film compression to the single-cycle regime combined with relativistic compression offers a method to transform conventional ultrafast laser pulses into attosecond X-ray laser pulses. These attosecond X-ray laser pulses are required to drive wakefields in solid density materials which can provide acceleration gradients of up to TeV/cm. Here we demonstrate a nearly 99% energy efficient compression of a 6.63 mJ, 39 fs laser pulse with a Gaussian mode to 20 fs in a single stage. Further, it is shown that as a result of Kerr-lensing, the focal spot of the system is slightly shifted on-axis and can be recovered by translating the imaging system to the new focal plane. This implies that with the help of wave-front shaping optics the focusability of laser pulses compressed in this way can be partially preserved.

We investigate 2-dimensional spatial optical solitons in media exhibiting a large nonlocal response coupled with a self-focusing nonlinearity. To this extent, with reference to a specific system in undoped nematic liquid crystals, we develop a general theory of spatial solitons in media with an arbitrary degree of nonlocality and carry out experimental observations to validate the model. The remarkable agreement between predictions and data yields evidence of narrow-waist solitons, revealing an important connection between nonparaxiality and nonlocality and emphasizing the role of nonlocality.

Photonic crystals create dramatic new possibilities for nonlinear optics. I suggest to use defect waveguides for the production of pairs of photons in order to achieve particular dispersion characteristics and potentially very high brightness. I identify two possible phase-matching schemes and discuss their properties and advantages.

High harmonic generation (HHG) has attracted tremendous attention over two decades. This paper presents a brief review of high harmonic generation in atoms, molecules and nanostructures. Through a simple classical model, we first review a few important concepts in HHG. We then discuss how the electric field initial phase affects the harmonic yield, and explain the reason behind the cutoff law. We focus on HHG in nanostructures. As an example, a detailed calculation in C₆₀ is presented.

Photoconductive and photorefractive characteristics of fullerene- and nanotubes-doped organic thin films based on conjugated organics, such as polyimide, polyaniline, pyridine, etc. have been studied. In addition, the liquid crystal mesophase with nanoobjects has been investigated. The increase of the charge carrier mobility of nanosensitized organics has been established. The nonlinear refraction and cubic nonlinearity have been investigated at wavelength of 532 nm via four-wave mixing technique using Raman-Nath diffraction regime. The thin holographic grating has been written at the spatial frequencies placed in the range of 90-150 mm^-1. The energy density has been chosen in the range of 0.1-0.9 J×cm^-2. The correlation between photoconductive and nonlinear optical parameters has been revealed. The nanostructured materials can be proposed for different area of nano- and microelectronic applications.

We investigated the optical bistability (OB), which is manipulated by double dark resonances, in a $\mathrm{\Lambda }$-type four-level atomic system with a unidirectional ring cavity. It is found that, with the interaction of double dark resonances, the bistable threshold intensity becomes weaker and the hysteresis loop becomes narrower by tuning properly the detuning of microwave field. Also, the influence of the intensity and frequency detuning of the microwave field on switching on or off the optical bistable behavior is studied, which is used to provide the theoretical guidance for controlling and optimizing all optical switching process. Our numerical results are explained by using a dressed-state approach.

An organic nonlinear single crystal of Nitrilotriacetic acid (NTAA) was grown for the first time by employing a simple slow evaporation technique. Single crystal X-ray diffraction (XRD) analysis reveals that the grown crystal belongs to the monoclinic system with noncentrosymmetric space group $C_C$. Fourier transform infrared (FTIR) spectral study ascertains the presence of functional groups in NTAA. The molecular structure of the grown crystal was confirmed by Nuclear Magnetic Resonance (NMR) spectral analysis. The optical parameters such as transmittance, absorption coefficient and band gap were calculated from UV–Visible and fluorescence studies. Dielectric measurements were carried out for different frequency and temperature. The mechanical strength of the grown crystal was measured using Vickers microhardness test. The high thermal stability and the melting point of the grown crystal were also estimated using thermogravimetric (TGA) and differential thermal analyses (DTA). The confirmation of the grown crystals belonging to nonlinear optical crystals was performed by Kurtz–Perry technique and found as suitable candidate for optoelectronics applications.

We identify a scheme in which we can control the behavior of an atomic medium to switch between optical bistability (OB) and optical multistability (OM) at multiple frequencies. The scheme relies on the absorption and dispersion characteristics of the optical medium at different frequencies, which can be modulated significantly by changing the magnetic field $B$ for tuning the energy difference between Zeeman sublevels. The result shows that the transition from OB to OM or vice versa can be easily realized not only at single frequency channel but also between multiple frequency channels. Furthermore, the optical steady-state behavior also varies with the ratio of the applied two coupling fields at any frequency channel. Such controllable switching between multiple frequency channels could also be used as some applications in all-optical switching and quantum information processing.

The structural dependence of nonlinear optical properties associated with ADP-doped PVA/PVP polymer composites is discussed in this work. Polymer composites are fabricated using the solution casting method. X-ray diffraction (XRD) was used to perform structural analysis on these samples whose average crystallite size increases with an increase in dopant concentration. Results from UV–Vis–NIR spectra show that the samples are transparent in the IR region. The Z-scan technique was established by following the method described by Sheik-Bahae et al. The shape of the open aperture plot suggests that the samples exhibit two-photon absorption. The NLO properties such as nonlinear absorption coefficient ($\beta )$, two-photon absorption cross-section (${\sigma }_2)$ and the imaginary part of third-order nonlinear susceptibility $({\chi }^{(3)})$ were investigated at 1064 nm and these values were found to be in the order of $\sim {10}^{-7}$W/cm, $\sim {10}^{-20}$cm⁴/GW and $\sim {10}^{-14}$esu, respectively. The open aperture Z-scan method yielded optical limiting data, from which the optical limiting threshold was calculated to be in the order of $\sim {10}^{13}$W/m². Functional data analysis uses a suitable basis representation to assess the functional correlation between global and local variables.

The single beam Z-scan technique was used to determine the nonlinear optical properties of the organic dye Nile Blue chloride in the solvent ethanol. The experiments were performed with a He-Ne laser with a wavelength of 632.8 nm. The negative nonlinear refractive index and two-photon absorption coefficient were observed in this dye. The intensity-dependent nonlinear refractive index was investigated. The result shows that the dye exhibits a great nonlinear response with the real and imaginary parts of the third-order nonlinear optical susceptibility χ⁽³⁾ being -4.12×10^-5 esu and 1.35×10^-6 esu, respectively. These results show that the Nile Blue chloride dye has potential applications in nonlinear optics.

The optical nonlinearity of an organic dye from a triphenylmethane group is measured using the Z-scan technique. The sample under study is found to exhibit the negative nature of nonlinearity, which is mainly due to the thermally induced refractive index change. Since this thermally induced refractive index change can lead to self-diffraction, the self-diffraction properties of the sample is studied by using thin films of a dye-sensitized gelatin. A He-Ne laser (633 nm) is used for both the Z-scan and self-diffraction studies. In the self-diffraction studies, it is also found that the different diffracted orders exhibit varying phase differences.

Based on dynamical diffraction theory, we study nonlinear processes in the hard X-ray region. First, we consider the process of frequency doubling in perfect crystals in the general case where the process of Bragg rescattering of the generated harmonic field should be taken into account. The optimum conversion conditions for the Bragg and Laue interaction geometry are determined and the efficiency is calculated. Secondly, we consider the modulation of X-ray diffraction by a wave of coherent optical phonons produced by an intense laser pulse. We show that in the optimum regime the modulation period of the X-ray beam may be even shorter than the period of the excited optical phonons, as a result of higher order Raman scattering. Generation of extremely short X-ray pulses using this technique is discussed. Our results suggest that synchronous interaction schemes analogous to the schemes long known in nonlinear optics can significantly increase the efficiency of nonlinear processes in the hard X-ray region.

Simple dimensional analysis of typical nonlinear optical phenomena in metal nanoparticles indicates that qualitatively new effects may be expected in nonlinear optics of surface plasmon polaritons. It appears that some of these effects are similar to well-known effects of quantum gravitational theory.

We present our results on nonlinear optical (NLO) of chicago sky blue 6B doped polyvinyl alcohol (PVA) film. This film was studied at 633 nm and 532 nm using a continuous wave laser. We have evaluated the sign and magnitude of the third-order nonlinearity from the closed aperture Z-scan data while the nonlinear absorption properties were assessed using the open aperture data. The chicago sky blue 6B doped PVA film exhibited nonlinear saturated absorption and strong self-defocusing effect. The limiting effect of the sample was studied and the results indicate that the film possesses good characteristic of optical limiting.

The third-order optical nonlinear properties of CdSe quantum dots (QDs) and CdSe-C₆₀ QDs are investigated by Z-scan technique with picosecond pulses at the wavelength of 800 nm. The value of the nonlinear absorption coefficient β of CdSe-C₆₀ QDs is measured to be 2.9 cm/GW, which is about two times larger than that of CdSe QDs. The nonlinear refraction index γ of CdSe-C₆₀ QDs is -2.8 × 10^-3cm²/GW, which is about seven times larger than that of CdSe QDs. Presence of C₆₀ contributes to the larger optical nonlinearity of CdSe-C₆₀ QDs comparing with CdSe QDs.