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1.
Nanotechnology ; 30(50): 505203, 2019 Sep 11.
Artigo em Inglês | MEDLINE | ID: mdl-31509805

RESUMO

Recently, rhenium diselenide (ReSe2) has attracted considerable attention due to its high anisotropy in the layer plane, which makes it a promising candidate for wide applications in electronics and optoelectronics. In this paper, we focus on the polarization-sensitive characteristics of a large-area multilayer ReSe2 nanofilm in the terahertz (THz) region under passive and active conditions by means of THz time-domain spectroscopy. We demonstrate the passive ReSe2 nanofilm with intrinsic THz polarization anisotropy. Maximum transmittance occurs only when the polarization direction of the incident THz wave is along the Re-chains direction. More importantly, THz polarization properties of the active ReSe2 nanofilm by an external electric field applied in a selected directions are also demonstrated. The modulation depth of the THz transmission is up to 16% and the response time is on the order of picoseconds. In addition, a comparative experiment is performed on three kinds of THz polarizers, i.e., ReSe2 nanofilm, carbon nanotubes (CNTs) and wire-gird, respectively. The results prove that the performance of the polarizer based on the active ReSe2 nanofilm is comparable with those of CNTs and the THz wire-gird polarizer. Based on these studies, we believe that the polarization-sensitive ReSe2 nanofilm can find important applications in ultrafast switches, filters and modulation devices in the THz region.

2.
J Vis Exp ; (149)2019 Jul 06.
Artigo em Inglês | MEDLINE | ID: mdl-31329179

RESUMO

Direct control of cellular defined molecular events is important to life science. Recently, studies have demonstrated that femtosecond laser stimulation can simultaneously activate multiple cellular molecular signaling pathways. In this protocol, we show that through coupling femtosecond laser into a confocal microscope, cells can be stimulated precisely by the tightly-focused laser. Some molecular processes that can be simultaneously observed are subsequently activated. We present detailed protocols of the photostimulation to activate extracellular signal regulated kinase (ERK) signaling pathway in Hela cells. Mitochondrial flashes of reactive oxygen species (ROS) and other mitochondrial events can be also stimulated if focusing the femtosecond laser pulse on a certain mitochondrial tubular structure. This protocol includes pretreating cells before photostimulation, delivering the photostimulation by a femtosecond laser flash onto the target, and observing/identifying molecular changes afterwards. This protocol represents an all-optical tool for related biological researches.

3.
Opt Express ; 27(6): 8808-8818, 2019 Mar 18.
Artigo em Inglês | MEDLINE | ID: mdl-31052693

RESUMO

We demonstrate a practical method that is used to generate on-demand first- and higher-order cylindrical vector beams, in the 1550 nm band, directly from an all polarization maintaining mode-locked Er-fiber laser. On demand typical 1st order CVBs, including the radially and azimuthally polarized beams, can be easily achieved by properly adjusting the angle of a half-wave plate with respect to the fast axis of the vortex wave plate. The spatial beam mode can be flexibly switched with no disturbance on the time domain mode-locking output. The laser outputs the desired vector beams at 1571 nm with a spectral bandwidth at full-width at half-maximum of 32 nm. The mode-locked laser pulses have a repetition rate of 74.9 MHz. Moreover, the proposed method can be easily extended to create higher-order CVBs. Our research provides a convenient way to generate ultrafast pulses in highly flexible-controlled structured modes, which is essential for optical fabrication and light trapping applications.

4.
Opt Lett ; 44(7): 1638-1641, 2019 Apr 01.
Artigo em Inglês | MEDLINE | ID: mdl-30933110

RESUMO

We propose a high-efficiency and compact 910-MHz femtosecond optical parametric oscillator, which is harmonically pumped by a ∼101 MHz Yb doped fiber laser system. The OPO is capable of delivering watt-level, power-enhanced signals across the telecommunication waveband. The signal power enhancement is realized by exploiting the bidirectional pumping technique. A maximum signal power of 1.04 W at 1502 nm is obtained for an input pump power of 3.8 W. Tunable near-infrared signal pulses with a wavelength range between 1350 and 1610 nm are measured, and the pulse durations vary from 193 to 464 fs. This compact and economic design provides a solution for efficient high repetition rate pulse generation over a large wavelength span, which will be beneficial for a variety of practical applications.

5.
Opt Lett ; 44(4): 1060-1063, 2019 Feb 15.
Artigo em Inglês | MEDLINE | ID: mdl-30768056

RESUMO

The f-to-2f interferometer plays a key role for carrier-envelope phase (CEP) measurement and subsequent stabilization. The CEP measurement typically relies on the application of two optical nonlinearities, namely supercontinuum generation and second-harmonic generation. Then the cascadation of these nonlinearities often leads to signal levels on the order of a few photons per pulse. We experimentally demonstrate that the introduction of optical gain into the infrared arm of an f-to-2f interferometer can mitigate this detection bottleneck and improve signal-to-noise ratios by 20 dB compared to purely passive schemes. We further show that this measure allows for residual phase jitters between the carrier and envelope of about 10 mrad, corresponding to record-breaking timing jitters in the single attosecond regime. Moreover, the method appears generally applicable to a wide range of oscillators in the near-infrared and may enable stable CEP locking of mode-locked oscillators that so far have resisted stabilization. Finally, we propose a parametric variant of the active f-to-2f interferometer that can be used for laser amplifiers with kilohertz repetition rates and below.

6.
Opt Lett ; 43(22): 5579-5582, 2018 Nov 15.
Artigo em Inglês | MEDLINE | ID: mdl-30439899

RESUMO

A high repetition-rate, few-cycle light pulse is of great importance due to its potential for a variety of applications, including two-dimensional infrared spectroscopy and time-resolved imaging of molecular structures, which benefit from its ultrabroadband spectrum and ultrashort pulse duration. The generation of an ultrabroadband coherent spectrum is one of the frontiers of ultrafast optics, and accessing such few-cycle pulses is presently under active exploration. Here, we demonstrate a simple yet effective pulse synthesizer. It is based on two continuous-wave (cw) injection-seeded high-repetition-rate optical parametric amplification systems and the following self-phase-modulation dominated spectra-broadening processes. The combined spectrum spans from 1250 to 1670 nm, and a near Fourier-transform-limited 3.9-cycle (19.2 fs) synthesized pulse with a central wavelength of 1470 nm is obtained accordingly.

7.
Opt Express ; 26(20): 26411-26421, 2018 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-30469729

RESUMO

Compressing picosecond laser pulses to the femtosecond level is an attractive shortcut for obtaining femtosecond laser pulses. However, dechirped pulses generated by nonlinear compression with self-phase modulation (SPM) show obvious pedestals, which are induced by nonlinear chirp accumulation in spectral broadening process and cannot be easily suppressed. Here, we report systematic numerical simulations and experimental studies on self-similar amplification of picosecond pulses in a short gain fiber for obtaining ~100-fs laser pulses with nearly transform-limited (TL) temporal quality. It is demonstrated that self-similar amplification with picosecond seed pulses is only sensitive to pulse duration and pulse energy. Based on this optimization guideline, we built a compact self-similar amplification fiber system with a picosecond fiber laser as the seed source. This system outputs 66-fs pulses with 6.1-W average power at a repetition rate of 30 MHz. Due to the linear chirp produced in self-similar evolution process, compressed pulses show nearly TL temporal quality. It promises an efficient way of obtaining high-quality femtosecond laser pulses from a picosecond laser source.

8.
Opt Express ; 26(22): 28302-28311, 2018 Oct 29.
Artigo em Inglês | MEDLINE | ID: mdl-30470004

RESUMO

We demonstrate an all polarization-maintaining (PM) fiber based dual-wavelength mode-locked Er-fiber laser. A nonlinear amplifying loop mirror (NALM) with an intracavity nonreciprocal phase shifter is used for self-started mode-locking. A short segment of PM fiber is angle-spliced to the NALM, functioning as a PM Sagnac loop filter, thus enabling dual-wavelength mode-locking. The wavelength separation is solely determined by the angle-spliced PM fiber length. Stable dual-wavelength mode-locking operation is switchable between 1570/1581 nm and 1581/1594 nm. The two-color pulse trains oscillating in the same cavity have an inherent offset repetition rate of ~1 kHz owing to cavity dispersion, allowing future high precision dual-comb applications with a simple and robust configuration.

9.
Opt Lett ; 43(13): 3108-3111, 2018 Jul 01.
Artigo em Inglês | MEDLINE | ID: mdl-29957798

RESUMO

Broadband characterization of the carrier-envelope phase (CEP) noise spectral density of free-running mode-locked lasers is essential for advanced low-noise optical frequency comb designs. Here we present a direct method that utilizes an optical heterodyne beat between a pair of repetition-rate-locked mode-locked lasers for CEP noise characterization, without requiring an f-2f interferometer or nonlinear optical conversion steps. A proof-of-principle experiment in a femtosecond Yb-fiber laser achieves CEP noise spectral density characterization with >270 dB dynamic range over a Fourier frequency range from 5 mHz to 8 MHz. The measurement noise floor is well below 1 µrad/√Hz, enabling dependable detection down to a quantum-limited noise floor. The method can resolve various noise mechanisms that cause specific CEP noise spectral shapes. The underlying mechanisms are further analyzed in terms of spurious temporal correlation to distinguish between technical and stochastic noise signatures. Moreover, a Hadamard deviation analysis reveals a varying degree of frequency stability in the measured CEP time series.

10.
J Biomed Opt ; 23(6): 1-6, 2018 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-29952149

RESUMO

Mitochondrial oxidative flashes (mitoflashes) are oxidative burst events in mitochondria. It is crosslinked with numerous mitochondrial molecular processes and related with pivotal cell functions such as apoptosis and respiration. In previous research, mitoflashes were found as spontaneous occasional events. It would be observed more frequently if cells were treated with proapoptotic chemicals. We show that multiple mitoflashes can be initiated by a single femtosecond-laser stimulation that was tightly focused on a diffraction-limited spot in the mitochondrial tubular structure. The mitoflash events triggered by different photostimulations are quantified and analyzed. The width and amplitude of mitoflashes are found very sensitive to stimulation parameters including laser power, exposure duration, and total incident laser energy. This study provides a quantitative investigation on the photostimulated mitoflashes. It may thus demonstrate such optical method to be a promising technique in future mitochondrial research.

11.
Opt Lett ; 43(12): 2848-2851, 2018 Jun 15.
Artigo em Inglês | MEDLINE | ID: mdl-29905705

RESUMO

The generation of high-power ultrashort pulses from a passively mode-locked fiber laser is reported based on the combination of a single-polarization large-mode-area (LMA) photonic crystal fiber with a nonlinear amplifying loop mirror design. The introduction of a non-reciprocal phase shift in the loop mirror enables self-starting of the mode-locked laser, while the polarizing LMA fiber supports environmentally stable high-power operation. Mode locking in the soliton-like, stretched-pulse, and all-normal-dispersion regime is characterized. The laser generates stable pulses with up to 2 W average power at a 72 MHz repetition rate, corresponding to a single-pulse energy of 28 nJ. The output pulses are dechirped to a near transform-limited duration of 152 fs. The proposed fiber oscillator presents an alternative approach to high-power ultrafast laser sources, along with environmental stability.

12.
Opt Lett ; 43(10): 2316-2319, 2018 May 15.
Artigo em Inglês | MEDLINE | ID: mdl-29762581

RESUMO

We demonstrate a high average power, widely tunable, dielectric-mirror-less optical parametric oscillator (OPO) based on MgO:PPLN (MgO-doped periodically poled lithium niobate), which is synchronously pumped by a 1040 nm femtosecond fiber laser. The OPO does not require any dielectric coating mirrors. By exploiting the four-prism sequence system, combined with the gold mirrors, the oscillating laser pulses could span the spectral regions in both the signal and idler, and the output pulses of OPO can be tuned across 1367-1914 nm in the signal, and 2152-4480 nm in the idler as well. This device can deliver as much as 1.2 W of average power at 1482 nm in the signal and up to 411 mW at 3487 nm in the idler, respectively. The ultrabroad-band spectra tunability, along with the high average output property, makes the dielectric-mirror-less OPO an attractive alternative to conventional OPOs.

13.
Opt Express ; 26(8): 11046-11054, 2018 Apr 16.
Artigo em Inglês | MEDLINE | ID: mdl-29716032

RESUMO

We demonstrate dual-comb spectroscopy in the vicinity of 2 µm wavelength based on a single dual-wavelength dual-comb Thulium-doped fiber laser. The shared laser cavity ensures passively maintained mutual coherence between the two combs due to common mode environmental noise rejection. In a proof-of-principle experiment, the absorption characteristics caused by the water in the optical path that composes the dual-comb spectrometer are measured. The retrieved spectral positions of the water absorption dips match with the HITRAN database.

14.
Opt Lett ; 43(7): 1623-1626, 2018 Apr 01.
Artigo em Inglês | MEDLINE | ID: mdl-29601046

RESUMO

In this work, we study the timing instability of a scalar twin-pulse soliton molecule generated by a passively mode-locked Er-fiber laser. Subfemtosecond precision relative timing jitter characterization between the two solitons composing the molecule is enabled by the balanced optical cross-correlation (BOC) method. Jitter spectral density reveals a short-term (on the microsecond to millisecond timescale) random fluctuation of the pulse separation even in the robust stationary soliton molecules. The root-mean-square (rms) timing jitter is on the order of femtoseconds depending on the pulse separation and the mode-locking regime. The lowest rms timing jitter is 0.83 fs, which is observed in the dispersion managed mode-locking regime. Moreover, the BOC method has proved to be capable of resolving the soliton interaction dynamics in various vibrating soliton molecules.

15.
Opt Express ; 25(25): 31263-31272, 2017 Dec 11.
Artigo em Inglês | MEDLINE | ID: mdl-29245803

RESUMO

We characterize the relative intensity noise (RIN) and relative timing jitter (RTJ) between the signal and pump pulses of optical parametric amplifiers (OPAs) seeded by three different seed sources. Compared to a white-light continuum (WLC) seeded- and an optical parametric generator (OPG) seeded OPA, the narrowband CW seeded OPA exhibits the lowest root-mean-square (RMS) RIN and RTJ of 0.79% and 0.32 fs, respectively, integrated from 1 kHz to the Nyquist frequency of 1.25 MHz. An improved numerical model based on a forward Maxwell equation (FME) is built to investigate the transfers of the pump and seed's noise to the resulting OPAs' intensity and temporal fluctuation. Both the experimental and numerical study indicate that the low level of noise from the narrowband CW seeded OPA is attributed to the elimination of the RIN and RTJ coupled from the noise of seed source, being one of the important contributions to RIN and timing jitter in the other two OPAs. The approach to achieve lower level of noise from this CW seeded OPA by driving it close to saturation is also discussed with the same numerical model.

16.
Opt Express ; 25(24): 30598-30605, 2017 Nov 27.
Artigo em Inglês | MEDLINE | ID: mdl-29221087

RESUMO

We propose a simple technique to scale the abruptly autofocusing beams in the direct space by introducing a scaling factor in the phase. Analytical formulas are deduced based on optical caustics, explicitly revealing how the scaling factor controls location, peak intensity, and size of the focal spot. We demonstrate that the multiplication of a scaling factor on the phase is equivalent to the axial-scaling transformation under the paraxial approximation. Further numerical and experimental results confirm theoretical predictions. In addition, amplitude modulation using phase-only holograms is used to maintain the peak intensity level of the focal spots.

17.
Opt Express ; 25(20): 24594-24603, 2017 Oct 02.
Artigo em Inglês | MEDLINE | ID: mdl-29041404

RESUMO

We study, both numerically and experimentally, the relative intensity noise (RIN) and timing jitter characteristics of optical parametric generation (OPG) process in MgO-doped periodically poled LiNbO3 (MgO:PPLN) pumped by fiber femtosecond laser. We directly characterize the RIN, and measure timing jitter spectral density of the OPG process based on the balanced optical cross-correlator (BOC) technique for the first time as well, which are both in a fairly good agreement with numerical simulation. Both the numerical and experimental study reveals that OPG can suffer from a smaller intensity fluctuation but a lager temporal jitter when it is driven into saturation. Furthermore, we demonstrate that with a 30 mW CW diode laser injection seeding the OPG output results in superior noise performance compared to the vacuum fluctuations seeded OPG.

18.
Opt Lett ; 42(10): 1923-1926, 2017 May 15.
Artigo em Inglês | MEDLINE | ID: mdl-28504760

RESUMO

A digital micromirror device (DMD)-based arbitrary spectrum amplitude shaper is incorporated into a large-mode-area photonic crystal fiber laser cavity. The shaper acts as an in-cavity programmable filter and provides large tunable dispersion from normal to anomalous. As a result, mode-locking is achieved in different dispersion regimes with watt-level high output power. By programming different filter profiles on the DMD, the laser generates femtosecond pulse with a tunable central wavelength and controllable bandwidth. Under conditions of suitable cavity dispersion and pump power, design-shaped spectra are directly obtained by varying the amplitude transfer function of the filter. The results show the versatility of the DMD-based in-cavity filter for flexible control of the pulse dynamics in a mode-locked fiber laser.

19.
Opt Express ; 25(7): 7559-7566, 2017 Apr 03.
Artigo em Inglês | MEDLINE | ID: mdl-28380877

RESUMO

We develop a practical femtosecond polarization-maintaining fiber laser amplification system with a standard double-cladding fiber technique, enabling 24-fs transform-limited pulses with 1-µJ pulse energy at a 1-MHz repetition rate. The laser system is based on a hybrid amplification scheme. Chirped-pulse amplification is employed in the pre-amplifier stage to supply high-quality pulses with enough energy for the main-amplifier, where nonlinear amplification is utilized to broaden the output spectrum. To obtain a dechirped pulse with high quality and short duration, a pre-shaper is inserted between the two amplification stages to adjust the pre-chirp, central wavelength, and pulse energy of the signal pulses in the main amplifier for optimizing pulse evolution. As a result, temporal pedestal free sub-ten-cycle high-energy laser pulses can be routinely obtained. In the end, the advantages of this novel laser source are demonstrated in the experiments on enhanced damage effect to cells co-cultured with gold nanorods.

20.
Opt Express ; 25(1): 10-19, 2017 Jan 09.
Artigo em Inglês | MEDLINE | ID: mdl-28085796

RESUMO

We demonstrate a novel time domain timing jitter characterization method for ultra-low noise mode-locked lasers. An asynchronous optical sampling (ASOPS) technique is employed, allowing timing jitter statistics on a magnified timescale. As a result, sub femtosecond period jitter of an optical pulse train can be readily accessible to slow detectors and electronics (~100 MHz). The concept is applied to determine the quantum-limited timing jitter for a passively mode-locked Er-fiber laser. Period jitter histogram is acquired following an eye diagram analysis routinely used in electronics. The identified diffusion constant for pulse timing agrees well with analytical solution of perturbed master equation.

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