Ultrafast Optics|43 Article(s)
Extending optical filaments with phase-nested laser beams
Jia-Qi Lü, Ping-Ping Li, Dan Wang, Chenghou Tu, Yongnan Li, and Hui-Tian Wang
Extending the length of femtosecond laser filamentation has always been desired for practical applications. Here, we demonstrate that significant extending of a single filament in BK7 glass can be achieved by constructing phase-nested beams. The filamentation and the following energy replenishment are assembled in a single phase-nested beam. The central part of the phase-nested beam is an apertured Gaussian beam, which is focused into one focal spot to produce a short filament. In contrast, the rest of the annular part converges gradually towards the central axis to continuously replenish the energy for supporting the regeneration of filaments. The common-path generating system ensures the stability of generated filaments and easily optimizes the beam parameters to obtain the longest high-quality filament due to its flexibility. In addition, we discuss the significance of continuous replenishment for extending filaments and the potential for generating more extended filaments based on this method.
Photonics Research
  • Publication Date: Nov. 19, 2018
  • Vol. 6, Issue 12, 12001130 (2018)
Effect of anti-crossings with cladding resonances on ultrafast nonlinear dynamics in gas-filled photonic crystal fibers
F. Tani, F. Köttig, D. Novoa, R. Keding, and P. St.J. Russell
Photonics Research
  • Publication Date: Jan. 24, 2018
  • Vol. 6, Issue 2, 02000084 (2018)
Clue to a thorough understanding of terahertz pulse generation by femtosecond laser filamentation
Jiayu Zhao, Weiwei Liu, Shichang Li, Dan Lu, Yizhu Zhang, Yan Peng, Yiming Zhu, and Songlin Zhuang
In this work, it has been demonstrated that in order to fully understand the terahertz (THz) pulse generation process during femtosecond laser filamentation, the interaction between THz wave and air plasma has to be taken into account. This interaction is mainly associated with the spatial confinement of the THz pulse by the plasma column, which could be described by the one-dimensional negative dielectric (1DND) waveguide model. By combining the 1DND model with the conventional four-wave mixing (4WM) and photocurrent (PC) models, the variation of THz spectral amplitude and width obtained in experiments could be better understood. Finally, a three-step procedure, with 1DND bridging 4WM and PC processes, has been established for the first time to describe the underlying mechanism of THz radiation from plasma sources.
Photonics Research
  • Publication Date: Mar. 27, 2018
  • Vol. 6, Issue 4, 04000296 (2018)
Valence state manipulation of Sm3+ ions via a phase-shaped femtosecond laser field
Ye Zheng, Yunhua Yao, Lianzhong Deng, Wenjing Cheng, Jianping Li, Tianqing Jia, Jianrong Qiu, Zhenrong Sun, and Shian Zhang
The ability to manipulate the valence state conversion of rare-earth ions is crucial for their applications in color displays, optoelectronic devices, laser sources, and optical memory. The conventional femtosecond laser pulse has been shown to be a well-established tool for realizing the valence state conversion of rare-earth ions, although the valence state conversion efficiency is relatively low. Here, we first propose a femtosecond laser pulse shaping technique for improving the valence state conversion efficiency of rare-earth ions. Our experimental results demonstrate that the photoreduction efficiency from Sm3+ to Sm2+ in Sm3+-doped sodium aluminoborate glass using a π phase step modulation can be comparable to that using a transform-limited femtosecond laser field, while the peak laser intensity is decreased by about 63%, which is very beneficial for improving the valence state conversion efficiency under the laser-induced damage threshold of the glass sample. Furthermore, we also theoretically develop a (2+1) resonance-mediated three-photon absorption model to explain the modulation of the photoreduction efficiency from Sm3+ to Sm2+ under the π-shaped femtosecond laser field.
Photonics Research
  • Publication Date: Jan. 30, 2018
  • Vol. 6, Issue 2, 02000144 (2018)
Optical forces of focused femtosecond laser pulses on nonlinear optical Rayleigh particles
Liping Gong, Bing Gu, Guanghao Rui, Yiping Cui, Zhuqing Zhu, and Qiwen Zhan
The principle of optical trapping is conventionally based on the interaction of optical fields with linear-induced polarizations. However, the optical force originating from the nonlinear polarization becomes significant when nonlinear optical nanoparticles are trapped by femtosecond laser pulses. Herein we develop the time-averaged optical forces on a nonlinear optical nanoparticle using high-repetition-rate femtosecond laser pulses, based on the linear and nonlinear polarization effects. We investigate the dependence of the optical forces on the magnitudes and signs of the refractive nonlinearities. It is found that the self-focusing effect enhances the trapping ability, whereas the self-defocusing effect leads to the splitting of the potential well at the focal plane and destabilizes the optical trap. Our results show good agreement with the reported experimental observations and provide theoretical support for capturing nonlinear optical particles.
Photonics Research
  • Publication Date: Jan. 26, 2018
  • Vol. 6, Issue 2, 02000138 (2018)
Improved common-path spectral interferometer for single-shot terahertz detection
Shuiqin Zheng, Qinggang Lin, Yi Cai, Xuanke Zeng, Ying Li, Shixiang Xu, Jingzhen Li, and Dianyuan Fan
To seek high signal-to-noise ratio (SNR) is critical but challenging for single-shot intense terahertz (THz) coherent detection. This paper presents an improved common-path spectral interferometer for single-shot THz detection with a single chirped pulse as the probe for THz electro-optic (EO) sampling. Here, the spectral interference occurs between the two orthogonal polarization components with a required relative time delay generated with only a birefringent plate after the EO sensor. Our experiments show that this interferometer can effectively suppress the noise usually suffered in a non-common-path interferometer. The measured single-shot SNR is up to 88.85, and the measured THz waveforms are independent of the orientation of the used ZnTe EO sensor, so it is easy to operate and the results are more reliable. These features mean that the interferometer is quite qualified for applications where strong THz pulses, usually with single-shot or low repetition rate, are indispensable.
Photonics Research
  • Publication Date: Feb. 14, 2018
  • Vol. 6, Issue 3, 03000177 (2018)
Chirp control of femtosecond-pulse scattering from drag-reducing surface-relief gratings
Juliane Eggert, Bjoern Bourdon, Stefan Nolte, Joerg Rischmueller, and Mirco Imlau
The role of chirp on the light–matter interaction of femto- and pico-second laser pulses with functional structured surfaces is studied using drag-reducing riblets as an example. The three-dimensional, periodic microstructure naturally gives rise to a mutual interplay of (i) reflection, (ii) scattering, and (iii) diffraction phenomena of incident coherent light. Furthermore, for femtosecond pulses, the structure induces (iv) an optical delay equivalent to a consecutive temporal delay of 230 fs in places of the pulse. These features enable studying experimentally and numerically the effect of tuning both pulse duration τ and spectral bandwidth Δω on the features of the wide-angle scattering pattern from the riblet structure. As a result, we discovered a significant breakdown of fringes in the scattering pattern with decreasing pulse duration and/or increasing spectral bandwidth. This unique type of chirp control is straightforwardly explained and verified by numerical modeling considering the spectral and temporal interaction between different segments within the scattered, linearly chirped pulse and the particular geometric features of the riblet structure. The visibility of the fringe pattern can be precisely adjusted, and the off-state is achieved using τ<230 fs or Δω>2.85×1013 rad/s.
Photonics Research
  • Publication Date: May. 02, 2018
  • Vol. 6, Issue 6, 06000542 (2018)
Ultrafast optical nonlinearity of blue-emitting perovskite nanocrystals
Junzi Li, Can Ren, Xin Qiu, Xiaodong Lin, Rui Chen, Cheng Yin, and Tingchao He
Perovskite nanocrystals (NCs) have strong nonlinear optical responses with a number of potential applications, ranging from upconverted blue-lasing to the tagging of specific cellular components in multicolor fluorescence microscopy. Here, we determine the one-photon linear absorption cross section of two kinds of blue-emitting perovskite NCs, i.e., CsPbCl3 and CsPb(Cl0.53Br0.47)3, by utilizing femtosecond transient absorption spectroscopy. The wavelength-dependent nonlinear refraction and two-photon absorption have been measured at wavelengths from 620 to 720 nm by performing Z-scan measurements. The nonlinear optical responses of CsPb(Cl0.53Br0.47)3 are much more pronounced than those of CsPbCl3 due to the larger structural destabilization of the former.
Photonics Research
  • Publication Date: May. 15, 2018
  • Vol. 6, Issue 6, 06000554 (2018)
Femtosecond laser-induced periodic surface structures on lithium niobate crystal benefiting from sample heating
Qiang Li, Qiang Wu, Yanan Li, Chunling Zhang, Zixi Jia, Jianghong Yao, Jun Sun, and Jingjun Xu
Periodic surface structures were fabricated by irradiating lithium niobate (LN) crystals with femtosecond laser pulses at sample temperatures ranging from 28°C to 800°C. Carrier density and conductivity of the samples were increased via heating LN, which inhibited coulomb explosion to obtain a uniform periodic surface structure. The periodic surface structures cover an area of 8 mm×8 mm and have an average spacing of 174±5 nm. Meanwhile, the absorption of the processed sample is about 70% in the spectral range of 400–1000 nm, which is one order of magnitude higher than that of pure LN. Fabrication of periodic surface structures on heating LN with femtosecond laser pulses provides a possibility to generate nanogratings or nanostructures on wide-bandgap transparent crystals.
Photonics Research
  • Publication Date: Jul. 10, 2018
  • Vol. 6, Issue 8, 08000789 (2018)
Overcoming the barrier of nanoparticle production by femtosecond laser ablation in liquids using simultaneous spatial and temporal focusing
Carlos Doñate-Buendía, Mercedes Fernández-Alonso, Jesús Lancis, and Gladys Mínguez-Vega
There exists an increasing demand of industrial-scale production of high-purity ligand-free nanoparticles due to the continuous development of biomedicine, catalysis, and energy applications. In this contribution, a simultaneous spatial and temporal focusing (SSTF) setup is first proposed for increasing nanoparticle productivity of the eco-friendly pulsed laser ablation in liquids (PLAL) technique. In spite of the fact that femtosecond pulses have proved to achieve higher ablation rates in air than picosecond pulses, in PLAL this is reversed due to the nonlinear energy losses in the liquid. However, thanks to the incorporation of SSTF, the energy delivered to the target is increased up to 70%, which leads to a nanoparticle production increase of a 2.4 factor. This breaks a barrier toward the employment of femtosecond lasers in high-efficiency PLAL.
Photonics Research
  • Publication Date: Oct. 24, 2019
  • Vol. 7, Issue 11, 11001249 (2019)