Shanghai Institute of Optics and Fine Mechanics,Chinese Academy of Sciences
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All-optical phase shifter and switch near 1550nm using tungsten disulfide (WS2) deposited tapered fiber
No full textNational Natural Science Foundation of China (NSFC) [61505105, 61675217, 61522510]; Shanghai Yangfan Program [14YF1401600]; Strategic Priority Research Program of CAS [XDB16030700]; Key Research Program of Frontier Science of CAS [QYZDB-SSW-JSC041]; STCSM Excellent Academic Leader of Shanghai [17XD1403900]; Open Fund of IPOC (BUPT)All-optical phase shifters and switches play an important role for various all-optical applications including all-optical signal processing, sensing and communication. In this paper, we demonstrate a fiber all-optical phase shifter using few-layer 2D material tungsten disulfide (WS2) deposited on a tapered fiber. WS2 absorbs injected 980 nm pump (control light) and generates heat, which changes the refractive index of both WS2 and tapered fiber due to thermo-optic effect and achieves a maximum phase shift of 6.1 pi near 1550 nm. The device has a loss of 3.7 dB. By constructing a Mach-Zehnder interferometer with WS2 based phase shifter in one arm, an all-optical switch is also obtained with an extinction ratio of 15 dB and a rise time of 7.3 ms. This all fiber low-cost and compact optical phase shifter and switch demonstrates the potential of 2D transition metal dichalcogenides for all-optical signal processing devices
Intense keV IAP generation by orthogonally polarized multicycle midinfrared two-color laser fields
No full textNational Natural Science Foundation of China [11127901, 61521093, 11134010, 11227902, 11574332, 1151101142, 61690223, 11274325]; Chinese Academy of Sciences [XDB16]; Youth Innovation Promotion Association of Chinese Academy of SciencesWe theoretically investigate the attosecond pulse generation in an orthogonal multicycle midinfrared two-color laser field. It is demonstrated that multiple continuum-like humps, which consist of about twenty orders of harmonics and an intensity of about one order higher than the adjacent normal harmonics, are generated when longer wavelength driving fields are used. By filtering these humps, intense isolated attosecond pulses (IAPs) are directly generated without any phase compensation. Our proposal provides a simple technique to generate intense IAPs with various central photon energies covering the multi-keV spectral regime by using multicycle midinfrared driving pulses with high pump energy in the experiment
Spectral modulation observed in artificial photosynthetic complexes by real-time vibrational spectroscopy
No full text100 Talents Program of Chinese Academy of Sciences (CAS), Strategic Priority Research Program of CAS [XDB1603, 61475169, 61521093, 11127901]; Japan Science and TechnologyBy real-time vibrational spectroscopy using 6.8 fs pulses, real-time vibronic coupling in stair-like zinc chlorin aggregates was studied. Besides the observed fast excitonic relaxation, amplitudes of coherent molecular vibrations are found to be linearly dispersed from the resonant peak as a function of their own vibrational frequencies. In addition, the initial phases of the molecular vibrations exhibiting clear pi phase jump have been observed. All these results indicate that coherent vibrations in the artificial chlorosome intermediate energy exchange between the laser fields around the resonant peak and those separated from it by photon energy equal to the vibrational frequencies
Waveform control of enhanced THz radiation from femtosecond laser filament in air
No full textStrategic Priority Research Program of the Chinese Academy of Sciences [XDB160104]; Key Project from Bureau of International Cooperation Chinese Academy of Sciences [181231KYSB20160045]; State Key Laboratory Program of the Chinese Ministry of Science and Technology; 100 Talents Program of Chinese Academy of Sciences; Laval University, Quebec City, CanadaWe report on a waveform control of enhanced THz radiation along a femtosecond laser filament in air with a high voltage technique. By applying a DC high-voltage electric field from two sharp electrodes in a direction parallel to the laser filament and scanning it along the filament, the longitudinal evolution of amplified THz emission was demonstrated. By changing the position of the pair of electrodes along the laser filament, different waveforms of THz radiation were obtained. Due to the change of the plasma density distribution at the leading and trailing ends of a laser filament, the enhanced THz waveforms could have a phase shift of similar to pi. The technique is very simple. It could help to understand the THz generation process through external electric field assisted laser filamentation. Published by AIP Publishing
Numerical simulations of 1 kHz, high-energy, broadband multipass amplification for a Ho:YLF chirped pulse amplification system
No full textWe demonstrate the high-gain of two double-pass Ho:YLF amplifiers with high-energy seed pulses injection via a modified population inversion Frantz-Nodvik model by numerical simulation. From the numerical simulation results, 26.2 mJ/1 kHz amplified pulses can be obtained by two double-pass amplifiers with 20 mu J/1 kHz, 40 nm (FWHM) bandwidth seed pulses injection. Due to similar to 1300 gain, the bandwidth of the amplified pulse decreases to about 3.5 nm (FWHM), corresponding to 466 fs pulse duration near 2 mu m wavelength. Therefore, the spectrum shaping of seed pulses is induced to suppress the gain narrowing effect. Then, the pulses can be amplified to 22.8 mJ with a spectrum of 16 nm (FWHM), which supports 368 fs pulse duration near 2 mu m by simulation
Image grating metrology using phase-stepping interferometry in scanning beam interference lithography
No full textLarge-sized gratings are essential optical elements in laser fusion and space astronomy facilities. Scanning beam interference lithography is an effective method to fabricate large-sized gratings. To minimize the nonlinear phase written into the photo-resist, the image grating must be measured to adjust the left and right beams to interfere at their waists. In this paper, we propose a new method to conduct wavefront metrology based on phase-stepping interferometry. Firstly, a transmission grating is used to combine the two beams to form an interferogram which is recorded by a charge coupled device(CCD). Phase steps are introduced by moving the grating with a linear stage monitored by a laser interferometer. A series of interferograms are recorded as the displacement is measured by the laser interferometer. Secondly, to eliminate the tilt and piston error during the phase stepping, the iterative least square phase shift method is implemented to obtain the wrapped phase. Thirdly, we use the discrete cosine transform least square method to unwrap the phase map. Experiment results indicate that the measured wavefront has a nonlinear phase around 0.05 [email protected]. Finally, as the image grating is acquired, we simulate the print-error written into the photo-resist
Dynamic three-dimensional multifocal spots in high numerical-aperture objectives
No full textNational Natural Science Foundation of China (NSFC) [61675093, 61705096]; Shandong Provincial Natural Science Foundation, China [ZR2017MA035]Multifocal spots in high numerical-aperture (NA) objectives has emerged as a rapid, parallel, and multi-location method in a multitude of applications. However, the typical method used for forming three-dimensional (3D) multifocal spots based on iterative algorithms limits the potential applications. We demonstrate a non-iterative method using annular subzone phases (ASPs) that are composed of many annular subareas in which phaseonly distributions with different 3D displacements are filled. The dynamic 3D multifocal spots with controllable position of each focal spot in the focal volume of the objective are created using the ASPs. The experimental results of such dynamic tunable 3D multifocal spots offer the possibility of versatile process in laser 3D fabrication, optical trapping, and fast focusing scanned microscopic imaging
Generation of square arrays of curved Bessel-like beams using continuous-phase encoding gratings
No full textNational Natural Science Foundation of China (NSFC) [61675093]We propose a scheme based on a type of continuous-phase encoding grating for the generation of multiple curved Bessel-like beams simultaneously. It is shown that multiple identical curved Bessel-like beams that diverge from a common center can be generated by overlapping a specially designed phase with a continuous-phase grating, and multiple high-order curved Bessel-like beams can be generated when another spiral phase is embedded. As an example, a 5 x 5 symmetric continuous-phase grating embedded with the special designed phase and a spiral phase is demonstrated based on a spatial light modulator. The experimental results show that 5 x 5 square arrays of bright- and dark-center curved Bessel-like beams were well generated. The proposed method provides an interesting method for obtaining simultaneously multiple curved Bessel-like beams, which should be of high interest for its promising applications in parallel optical manipulation, optical guiding, laser machining or laser surgery, particle acceleration, etc
On the difference between single- and double-sided bandpass filtering of spatial frequencies
No full textNational Natural Science Foundation of China [61405214, 61308077]It is well-known that bandpass filtering will lead to edge extraction in image processing. However, the difference between single-and double-sided bandpass filtering has never been compared and investigated in the literature. We investigate the difference between single-and double-sided bandpass spatial filtering in a 4-f coherent optical image processing system. We find that single-sided filtering can approximate the operation of a first-order derivative, while double-sided filtering gives a second-order derivative. Simulations and optical experiments confirm our findings
Optimal defocus selection based on normed Fourier transform for digital fringe pattern profilometry
No full textNational Natural Science Foundation of China (NSFC) [61474129]; World Academy of Sciences (TWAS); Chinese Academy of Sciences (CAS)Owing to gamma-effect robustness and high-speed imaging capabilities, projector defocusing of binary-coded fringe patterns is by far the most widely used and effective technique in generating sinusoidal fringe patterns for three-dimensional optical topography measurement with digital fringe projection techniques. However, this technique is not trouble-free. It is borne with uncertainty and challenges mainly because it remains somewhat difficult to quantify and ascertain the level of defocus required for desired fidelity in sinuousness of the projected fringe pattern. Too much or too little defocusing will affect the sinuosity accuracy of fringe patterns and consequently jeopardize the quality of the measurement results. In this paper, by combining intrinsic phase spectral sensitivities and normed Fourier transform, a method to quantify the amount of defocus and subsequently select the optimal degree of sinuosity for generating digital sinusoidal fringe patterns with projector defocusing for fringe pattern optical three-dimensional profilometry is proposed. Numerical simulations plus experiments give evidence of the feasibility and validity of the proposed method in enabling an improved digital binary defocusing technique for optical phase-shift profilometry using the digital fringe projection technique