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Thomas G Mayerhöfer, Jürgen Popp
We show that an electric field standing wave effect is responsible for the oscillations and the non-linear dependence of the absorbance on the layer thickness in thin layers on a reflective surface. This effect is connected to the occurrence of interference inside these layers. Consequently, the absorptance undergoes a maximum electric field intensity enhancement at spectral positions close to those where corresponding non-absorbing layers on a metal show minima in the reflectance. The effect leads to changes of peak maxima ratios with layer thickness and shows the same periodicity as oscillations in the peak positions...
October 11, 2017: Spectrochimica Acta. Part A, Molecular and Biomolecular Spectroscopy
Patrick W Wright, Lindsey M Brier, Adam Q Bauer, Grant A Baxter, Andrew W Kraft, Matthew D Reisman, Annie R Bice, Abraham Z Snyder, Jin-Moo Lee, Joseph P Culver
The interplay between hemodynamic-based markers of cortical activity (e.g. fMRI and optical intrinsic signal imaging), which are an indirect and relatively slow report of neural activity, and underlying synaptic electrical and metabolic activity through neurovascular coupling is a topic of ongoing research and debate. As application of resting state functional connectivity measures is extended further into topics such as brain development, aging and disease, the importance of understanding the fundamental physiological basis for functional connectivity will grow...
2017: PloS One
Sayan Bayan, Narendar Gogurla, Anupam Midya, Achintya Singha, Samit K Ray
We demonstrate the surface plasmon induced enhancement and tunablilty in optical emission properties of two dimensional (2D) graphitic carbon nitride (g-C3N4) nanosheets through the attachment of gold (Au) nanoparticles. Raman spectroscopy has revealed the event of surface enhanced Raman scattering that arises due to the combined effect of charge transfer process and localized surface plasmon induced enhancement in electromagnetic field, both occurring at the nanoparticle-nanosheet interface. Photoluminescence studies suggest that at an optimal concentration of nanoparticles, the emission intensity can be enhanced which is maximum within 500-525 nm region...
October 19, 2017: Nanotechnology
Qing Han, Yue Wen, Jian-Cai Liu, Wu Zhang, Li-Juan Chen, Jun-Wei Zhao
A series of organic-inorganic rare-earth-incorporated tellurotungstate hybrids, Na4[RE2(H2O)4(pica)2W2O5][(RE(H2O)W2(Hpica)2O4)(B-β-TeW8O30H2)2]2·38H2O (RE = La(III) (1), Ce(III) (2), Nd(III) (3), Sm(III) (4), Eu(III) (5); Hpica = 2-picolinic acid), were prepared via a one-step assembly reaction of Na2WO4·2H2O, RE(NO3)3·6H2O, K2TeO3, Hpica, and triethylamine (tea). Notably, the solubilization of tea toward Hpica and the solubilization of Hpica toward RE cations in the reaction system play an important role in the formation of 1-5...
October 19, 2017: Inorganic Chemistry
Longxiang Peng, Yantang Huang, Yafan Duan, Shijian Zhuang, Tingdi Liao, Canhua Xu
2 μm laser oscillation with a low threshold has been achieved in Ho(3+):Tm(3+)-codoped silica microspheres (HTCSMs). Ho(3+):Tm(3+)-codoped solgel functionalization film is applied to the surface of a silica microsphere, and an optical tapered fiber is adopted to couple an 808 nm continuous-wave laser to serve as the pump light source. Multimode and single-mode laser oscillations around 2 μm within the eye-safe wave band are observed due to the I75→I85 transitions of Ho(3+) ions sensitized by Tm(3+). The morphology characteristics of microspheres determine the multimode laser oscillation spectrum...
September 10, 2017: Applied Optics
Saeed Abdolhosseini, Reza Kohandani, Hassan Kaatuzian
This paper represents the influences of temperature and hydrostatic pressure variations on GaAs/AlGaAs multiple quantum well slow light systems based on coherence population oscillations. An analytical model in non-integer dimension space is used to study the considerable effects of these parameters on optical properties of the slow light apparatus. Exciton oscillator strength and fractional dimension constants have special roles on the analytical model in fractional dimension. Hence, the impacts of hydrostatic pressure and temperature on exciton oscillator strength and fractional dimension quantity are investigated theoretically in this paper...
September 10, 2017: Applied Optics
Bin Liu, Yanguang Yu, Jiangtao Xi, Qinghua Guo, Jun Tong, Roger A Lewis
A laser diode (LD) with external optical feedback can generate undamped relaxation oscillation (RO) under certain operational conditions. The RO frequency can be modified by the external cavity length of the LD and is highly sensitive to the variation of the cavity length (ΔL). This work first investigates the relationship between the RO frequency and ΔL by solving the well-known Lang-Kobayashi (L-K) equations and then verifies the relationship by experiments. Both theory and experiment show that the RO frequency changes in a sawtooth-like quasi-periodic manner with respect to ΔL...
August 20, 2017: Applied Optics
T Petersen, J D Zuegel, J Bromage
An ultrafast, high-average-power, extended-cavity, femtosecond BiB3O6 optical parametric oscillator was constructed as a test bed for investigating the scalability of infrared parametric devices. Despite the high pulse energies achieved by this system, the reduction in slope efficiency near the maximum-available pump power prompted the investigation of thermal effects in the crystal during operation. The local heating effects in the crystal were used to determine the impact on both phase matching and thermal lensing to understand limitations that must be overcome to achieve microjoule-level pulse energies at high repetition rates...
August 20, 2017: Applied Optics
Xin Liu, Xuewen Shu
All-optical fractional-order temporal differentiators with bandwidths reaching terahertz (THz) values are demonstrated with transmissive fiber Bragg gratings. Since the designed fractional-order differentiator is a minimum phase function, the reflective phase of the designed function can be chosen arbitrarily. As examples, we first design several 0.5th-order differentiators with bandwidths reaching the THz range for comparison. The reflective phases of the 0.5th-order differentiators are chosen to be linear phase, quadratic phase, cubic phase, and biquadratic phase, respectively...
August 20, 2017: Applied Optics
Quanxin Na, Chunqing Gao, Qing Wang, Yixuan Zhang, Mingwei Gao, Meng Zhang, Yujia Wang
In this paper, we report the experimental realization of a high-repetition-rate single-frequency Ho-doped yttrium aluminum garnet (Ho:YAG) ring laser at 2.09 μm. Single-frequency operation of the ring laser is achieved by injection-seeding with a continuous wave (CW) Ho:YAG non-planar ring oscillator (NPRO) laser. The output energy of the ring laser is 6.24 mJ with a pulse width of 172 ns and a repetition rate of 1 kHz. The beam quality M(2)-factor is measured to be ∼1.3 at the maximum output energy...
September 1, 2017: Applied Optics
William E Vargas
Three parametric models of Drude-Lorentz (DL) are used to describe the spectral variation of the dielectric function of bulk palladium. An improved version of the acceptance-probability-controlled simulated annealing method is applied to optimize the values of the parameters involved in the models: high-frequency dielectric constant, free-electron collision frequency and corresponding relaxation time, oscillation strengths, nominal resonance frequencies, and Lorentzian widths. Normalization of the oscillation strengths allows the introduction of a new parameter in the context of the original DL model: the number density ratio, which is the ratio between the number density of conduction electrons and the number density of metal atoms...
August 10, 2017: Applied Optics
Mahbube Khabbaz, Mohammad Sabaeian, Hamid Nadgaran
In this paper, a model describing the thermal effects on the optical parametric oscillator (OPO) of Gaussian continuous waves in double-pass cavities is presented. Eight equations, including forward and backward nonlinear waves, heat, and thermally induced phase mismatching equations, were coupled and solved simultaneously to investigate the effect of heat generation on the OPO's efficiency. The model was applied for a periodically poled MgO:LiNbO3 crystal with an excellent agreement with experimental data...
August 10, 2017: Applied Optics
A A Ryzhov
A multilayer GaAs/AlAs heterostructure forming a Fabry-Perot microcavity with a narrow resonance at 1.1 μm was produced by molecular-beam epitaxy. Under nanosecond pulsed laser radiation, a blueshift of the resonant line, associated with a photo-induced negative change in refractive index in GaAs, was experimentally registered by using an optical parametric oscillator. The spectral shift was accompanied by a reduction in peak transmittance, associated with nonlinear intracavity absorption. Such a cavity can be used as an optical limiter at the resonant wavelength when both the spectral shift and the transmittance reduction contribute to the limiting effect...
July 20, 2017: Applied Optics
Kentaro Miyata, Valentin Petrov, Kiyoshi Kato
This paper reports on the new experimental results for second-harmonic generation and sum-frequency generation in LiGaSe2 in the 1.026-10.5910 μm range, and the improved Sellmeier equations that provide a good reproduction of the present experimental results, as well as the published data points for a Ti:Al2O3 laser (λ=0.8200  μm)-pumped optical parametric amplifier and a Nd:YAG laser-pumped optical parametric oscillator in the mid-IR.
August 1, 2017: Applied Optics
Xueying Jin, Jing Wang, Mengyu Wang, Yongchao Dong, Fei Li, Keyi Wang
Controlling dispersion of a whispering gallery mode resonator is of critical importance for many nonlinear applications, such as frequency comb generation, parametric oscillators, Raman lasers, stimulated Brillouin lasers, and ultrafast optics. Here, we show by numerical and theoretical modeling that dispersion can be strongly engineered in a three-layer-coated microsphere of high, low, and high refractive indices (RIs). We investigate the impact of the coating thickness, the gap between the two high-RI layers, the surrounding medium, and the coating materials on the group-velocity dispersion and discover that the dispersion is controllable over a broad range in both normal and anomalous dispersion regimes...
October 1, 2017: Applied Optics
Sajad Jahanbakht
A frequency domain algorithm is proposed for deriving all of the possible steady state modes of dual injection-locked optoelectronic oscillators (DIL-OEOs), corresponding to the detailed system parameters, such as the fiber lengths, small signal open loop gains, radio frequency filters' bandwidths, phase shifting values, and injection parameters. It is shown that some or all of the modes computed by the new approach may be unstable; these are just mathematical solutions of the steady state equations. Therefore, it is necessary to check the stability of these modes...
July 10, 2017: Applied Optics
Ayman Alismail, Haochuan Wang, Najd Altwaijry, Hanieh Fattahi
We report on a simple scheme to generate broadband, μJ pulses centered at 2.1 μm with an intrinsic carrier-envelope phase (CEP) stability from the output of a Yb:YAG regenerative amplifier delivering 1-ps pulses with randomly varying CEP. To the best of our knowledge, the reported system has the highest optical-to-optical efficiency for converting 1-ps, 1 μm pulses to CEP stable, broadband, 2.1 μm pulses. The generated coherent light carries an energy of 5.4 μJ, at 5 kHz repetition rate, that can be scaled to higher energy or power by using a suitable front end, if required...
June 10, 2017: Applied Optics
Lei Li, Meng Wang, Tong Liu, Jinyong Leng, Pu Zhou, Jinbao Chen
We demonstrate, to the best of our knowledge, the first cladding-pumped all-fiber oscillator configuration with selective transverse mode generation based on a mode-selective fiber Bragg grating pair. Operating in the second-order (LP11) mode, maximum output power of 4.2 W is obtained with slope efficiency of about 38%. This is the highest reported output power of single higher-order transverse mode generation in an all-fiber configuration. The intensity distribution profile and spectral evolution have also been investigated in this paper...
June 10, 2017: Applied Optics
Kewei You, Yanli Zhang, Xuejie Zhang, Mingying Sun, Jianqiang Zhu
The structural evolution of the axial intensity distribution during hot image formation perturbed by a small circular optical obscuration is investigated in detail under different conditions. An analytic expression is derived for the axial intensity distribution around the conjugate plane by assuming the thickness of the nonlinear medium to be infinitely small. In view of the analysis of the axial intensity oscillation, the expression can be extensively utilized to characterize the intensity maxima for a nonlinear medium with a finite thickness...
June 1, 2017: Applied Optics
Xun Lei, Zenghui Gu, Jianbin Ma, Guanshi Qin, Zhanguo Chen, Shaowu Chen
We numerically simulate Kerr comb generation in an anomalous dispersion microcavity by modal expansion method and demonstrate that the initiation of comb generation is affected by the change of local dispersion possibly caused by avoided mode crossings. We also quantitatively analyze the instantaneous phase matching of different modes and reveal the characteristics of energy distribution in different modes in the dynamics of comb generation. We demonstrate that the local dispersion change can control the Kerr comb to transform between Type I and Type II combs...
June 1, 2017: Applied Optics
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