Experimental observation of reverse wavelength self-sweeping effect is reported in a bidirectional ytterbium-doped fiber ring laser. The wavelength self-sweeping regime - that a spontaneous, periodical, stable - can be obtained by the dynamical induced grating formed in an active medium due to the spatial hole burning. In this work, the reverse self- sweeping effect operates, for the first time, to the best of our knowledge, in 1.037 μm wavelength region. Besides, the fiber laser can generate a self-pulse signal and reverse wavelength self-sweeping with an average rate of 0.38 nm/s in the largest coverage of 2.75 nm. The self-pulse signal that modulated by inter-mode beating can be observed and the microsecond pulse train envelopes are in the range of 116-128 kHz.
We present stable dispersion-managed soliton (DMS) molecules in a passively mode-locked Yb-doped polarization-maintaining fiber laser based on chirped fiber Bragg grating in the anomalous dispersion regime. The generation of DMSs are characterized by their sech2-like spectral profile with no steep spectral edges, which is distinct from those of dissipative solitons generated in Yb-doped fiber lasers with a large net positive cavity group velocity dispersion regime. The pulse width is 4.8 ps if the sech2 profile is assumed. The corresponding pulses width could be compressed to 278 fs with grating pair compressor. Furthermore, DMS molecules exhibit multiple discrete equilibrium distances and a regular spectral modulation pattern. All these DMS molecules are stable in the sense that after being obtained they can remain several days. The proposed laser proves its great potential to future practical use in high-resolution optics for coding and optical communication.
The current state of single frequency fiber laser technology based on different saturable absorbers (SA) is reviewed. The proposed and experimental fiber lasers used ytterbium-doped fiber (YDF) as the gain medium and the mode selection is done by Sagnac interferometer loop mirror filter (LMF) incorporated SA. In this paper, we review the experiment principle and process of SF fiber lasers utilizing different function materials as the SA, including the fabrication, features of the two-dimensional (2-D) materials (graphene and molybdenum disulfide film) SA. The SA is like a narrowband filter to ensure the longitudinal mode operation. Finally, we systematically analysis and compare the experimental results based on different SA.
We analyzed graphically the resonator stability versus the thermal focal length and the thermally induced birefringence, as well as the fundamental spot size on the laser rod for a green laser of Nd:Y3Al5O12 (Na:YAG) on high-gray-tracking-resistivity KTiOPO4 as a function of the pumping power for r- and -polarization beams. The spot size distribution of the second harmonic and the fundamental wave in the folded cavity are also presented. On the basis of the theoretical analysis, an average power of 185.21 W was obtained with an intracavity frequency-doubling two-diode-side-pumped Nd:YAG laser system with twin acoustic-optical modulators, and the pulse width was 180 ns at a repetition rate of 10 kHz when the pumping power of each laser diode module was 600 W. The optical-to-optical conversion efficiency was 15.4%, and the beam quality factors were M=9.52, M=9.86.
Experiments were carried out using the tomato (Lycopersicon esculentum) stored at 28°C and 4°C , at the same time, the
spontaneous ultra-weak photon emission (UPE), delayed luminescence (DL), ethylene releasing, respiratory intensity,
chroma main wavelength and chlorophyll content were detected. It was found that: The curve of the spontaneous UPE is
just consists with respiratory intensity at 28°C and relate to chlorophyll content variation. The experiment data were
given guide line to noninvasive test maturity, DL data were dealt with curve fitting and compared with coherent theory.
Nanometer TiO2 thin films are prepared by a sol-gel method and the effects of preparation technique on the microstructure and surface morphology of the obtained materials are studied using X-ray Diffraction [XRD,IR spectrum[IR], UV-VIS spectrum [UV-VIS,AFM and X-ray photoelectron spectroscopy[XPS]. The results show that the TiO2 thin films are of anatase and rutile phase structures when annealed in a temperature range from 450°C to 600°C. When heated up to 700°C, the structure of TiO2 film changed into rutile completely. In the TiO2 thin films, there is some residual carbon from the starting organometallic components and a small amount of sodium ions diffused from the glass substrates. During heat-treatment, the absorption peak of water become weak gradually and the organic groups are disappeared completely at 500°C. Optimum film layers are obtained for the UV absorbance index. AFM result shows that the rough morphology of surface [RMS] of films is about 2-3nm or so.
A 3 x 3 order matrix formalism for describing dispersion system conveniently is achieved by introducing an angular dispersion term based on ABCD matrix formalism. The matrix formalism is used to compute the second and third order time dispersion of the aberration-free stretcher. The same conclusion as the one achieved using the way of routine integral and ray trace is obtained. It is proven that computing the time delay dispersion of any dispersion systems using matrix formalism not only is convenient but also can offer more information about systems. In addition, this way is suitable for any dispersion systems.
Chirped pulse amplification(CPA) has become a common technique for the generation of ultrashort and high peak power femtosecond(fs) optical pulses. One key point of this technique is the reasonable design for the pulse stretcher. We improved the aberration—free stretcher replacing the two spherical mirrors with two concentric rectangular focused cylindrical ones. The first mirror is convex, and the second one concave. Their radius of curvature ratio is two and of opposite sign. This combination cancels spherical aberration and astigmatism, and has no on-axis coma and exhibits no chromatic aberration. We calculated the group velocity dispersion(GVD) of the stretcher by ray-tracing model. Supposing that the distance between the grating and the center of curvature is a variable 1, we obtained the variety of the group delay and the GVD of the stretcher with the parameter 1 and the incidence wavelength A .For the input pulse, let pulsewidth to 9.8fs , the initial chirp C=O.75, the distance l=O.lm, we gained GVD was 2.5fs2/jm for the center wavelength 790nm, the stretching factor was 90197.4, that is, the seed pulse(9.8fs in duration) can be stretched to 884 PS
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