2015, 13(5) Column
Chinese Optics Letters 第13卷 第5期
We experimentally demonstrate N 2 + lasing actions at the wavelengths of 353.3, 353.8, and 354.9 nm using a circularly polarized femtosecond laser. The three laser lines correspond to the B 2 Σ u + ( v ′ = 5,4 , 3 ) → X 2 Σ g + ( v = 4 , 3 , 2 ) transitions, respectively. Particularly, we reveal the pressure-dependent gain dynamics of these lasing actions from highly excited vibrational states with a pump–probe scheme. Our experimental results confirm that electron collisional excitation plays an important role in the establishment of a population inversion of N 2 + lasing at these wavelengths.
020.2649 Strong field laser physics 320.7150 Ultrafast spectroscopy 320.2250 Femtosecond phenomena Selection of odd or even harmonics by a multi-color laser field with macroscopic phase-matchingDownload:965次
We experimentally and theoretically demonstrate that the property (odd or even) of generated harmonics can be selected by manipulating the macroscopic phase-matching conditions based on a three-color laser field. Only odd or even harmonics can be made dominant by changing the focal position and adjusting the gas pressure. These results indicate that the odd-even property of the generated harmonics can be controlled by using the multi-color laser field with macroscopic phase-matching.
020.1335 Atom optics 020.2649 Strong field laser physics 190.2620 Harmonic generation and mixing Two-dimensional apodized grating couplers are proposed with grating grooves realized by a series of nano-rectangles, with the feasibility of digital tailoring the equivalent refractive index of each groove in order to obtain the Gaussian output diffractive mode in order to enhance the coupling efficiency to the optical fiber. According to the requirement of leakage factor distribution for a Gaussian output profile, the corresponding effective refractive index of the grating groove, duty cycle, and period are designed according to the equivalent medium theory. The peak coupling efficiency of 93.1% at 1550 nm and 3 dB bandwidth of 82 nm are achieved.
050.2770 Gratings 050.6624 Subwavelength structures 050.2065 Effective medium theory A new tunable microwave photonic notch filter with negative coefficients is presented. It is based on a polarization modulator and a polarization beam interferometer. Experimental results are presented that embody the new concept.
060.5625 Radio frequency photonics 070.2615 Frequency filtering 230.0250 Optoelectronics A novel fiber-optic magnetic field sensor is demonstrated based on a dual-polarization fiber-grating laser, which is embedded in an epoxy resin-bonded magnetostrictive composite material with doped Terfenol-D particles. A simple structure is designed to convert the magnetic field-induced strain to transversal stress, which is applied to the fiber laser to produce beat note frequency changes for measurement purposes. The response of the proposed sensor is measured, and shows quite a good directivity and linearity with a sensitivity of 10.5 Hz/μT to the magnetic field. It also shows a large measurable range up to about 0.3 T.
060.2370 Fiber optics sensors 280.3420 Laser sensors Hybrid fiber interferometer for simultaneous measurement of displacement and temperatureDownload:878次
A hybrid fiber interferometer sensing configuration for displacement and temperature measurements is proposed and experimentally demonstrated that is constructed by splicing a short section of polarization maintaining optical fiber to an end-cleaved single mode optical fiber with a tapering structure. The reflected spectrum changes with the variation of displacement and temperature. The sensing configuration uses the method of wavelength and intensity modulations for displacement and temperature measurements, respectively, to which the sensitivities are 0.01392 nm/μm, 0.0214 dBm/μm, 0.09136 nm / ° C , and 0.15795 dBm/°C. Experimental results show that displacement and temperature can be measured simultaneously by demodulating the reflected spectrum.
060.0060 Fiber optics and optical communications 060.2310 Fiber optics 060.2370 Fiber optics sensors Performance analysis of space-shift keying over negative-exponential and log-normal FSO channelsDownload:1288次
The average bit-error rate (ABER) performance of free-space optical (FSO) communication links is investigated for space-shift keying (SSK) over log-normal and negative-exponential atmospheric turbulence channels. SSK is compared with repetition codes and a single-input single-output system using multiple pulse amplitude modulations. Simulation results show that the signal-to-noise ratio gain of SSK largely increases with greater spectral efficiencies and/or higher turbulence effects. A tight bound for ABER is derived based on an exact moment generation function (MGF) for negative-exponential channel and an approximate MGF for log-normal channel. Finally, extensive Monte Carlo simulations are run to validate the analytical analysis.
010.1300 Atmospheric propagation 010.1330 Atmospheric turbulence 060.4510 Optical communications 3D image reconstruction with a controllable overlapping number of elemental images in computational integral imagingDownload:943次
In this Letter, we propose a three-dimensional (3D) image reconstruction method with a controllable overlapping number of elemental images in computational integral imaging. The proposed method can control the overlapping number of pixels coming from the elemental images by using the subpixel distance based on ray optics between a 3D object and an image sensor. The use of a controllable overlapping number enables us to provide an improved 3D image visualization by controlling the inter-pixel interference within the reconstructed pixels. To find the optimal overlapping number, we simulate the pickup and reconstruction processes and utilize the numerical reconstruction results using a peak signal-to-noise ratio (PSNR) metric. To demonstrate the feasibility of our work in optical experiments, we carry out the preliminary experiments and present the results.
110.0110 Imaging systems 110.6880 Three-dimensional image acquisition Novel calibration optical path of cryogenic radiometerDownload:1123次
We introduce a novel calibration optical path of the cryogenic radiometer, which can avoid the repeated dismounting measurement and eliminate the negative influence of Brewster window effect on calibration result. The novel calibration optical path is used to calibrate the absolute spectral responsivity of the standard transfer detector at 633 nm, the results of which are compared with the ones of the previous structure. It is shown that comparing the previous results to the structure optimization, the measurement uncertainty of laser power reduces by a factor of 2, the measurement uncertainty on the absolute spectral responsivity of the transfer detector decreases by 15%, and the consistence of the calibration on absolute spectral responsivity is 4.0 × 10 3 . The experiment result proves that the novel calibration optical path of cryogenic radiometer can effectively reduce the calibration uncertainty against standard detector and improve the accuracy of calibration.
120.3930 Metrological instrumentation 120.3940 Metrology 120.4570 Optical design of instruments 120.4640 Optical instruments 120.4800 Optical standards and testing We present a compact displacement measurement system possessing the capability of nanometer-scale precision. On basis of integrating single grating with 3 × 3 coupler for phase shift in interference signal, the present scheme features advantages of simple structure, convenient alignment, and insensitivity to air turbulence. Linear comparisons between our system and HP5530 show a residual error less than 81 nm during step motions along a 10 mm round-trip, and a discrepancy less than 15 nm in the case of 200 μm movement. We also demonstrate a measurement stability test in a duration of 300 s, which shows the proposed scheme potentially performs better than HP5530 in terms of long-term stability.
050.1950 Diffraction gratings 060.2430 Fibers, single-mode 060.2920 Homodyning We report a direct, modulated bandwidth enhancement in a amplified feedback laser (AFL), both experimentally and numerically. By means of fabricated devices, an enhanced 3 dB bandwidth of 27 GHz with an in-band flatness of ± 3 dB is experimentally confirmed at 13 °C. It is numerically confirmed that the modulated bandwidth of the AFL can be enhanced to two times its original bandwidth, with more controlled flexibility to realize a flat, small-signal response.
140.5960 Semiconductor lasers 130.3120 Integrated optics devices 060.4510 Optical communications In this Letter, a gray-tracking-resistant—potassium titanyl phosphate (GTR-KTP) crystal is used for intracavity frequency doubling red laser generation for the first time. Under the 808 nm LD pump power of 180 W, as high as 12.5 W of red laser output is obtained with the optimum repetition rate of 7 kHz. Within the red laser power variation range between the maximum to 70%, a temperature tolerance is measured to be 35°C. The results prove that GTR-KTP should be a potential nonlinear crystal for red laser generation.
140.3480 Lasers, diode-pumped 140.3580 Lasers, solid-state Resonant effect is found in femtosecond laser ablating Pr–Nd glass. When processed with resonant wavelength of 807 nm, resonant ablation efficiency (RAE) with a single pulse can be improved by 45.22%. Furthermore, RAE closely relates to laser intensity. For resonant ablation, RAE is increased significantly when laser intensity < 0.556 × 10 14 W / cm 2 at which multiphoton ionization dominates, while it fades away when laser intensity > 0.556 × 10 14 W / cm 2 at which tunnel ionization dominates. Besides, it is also found that the ablation depth increases along with the wavelength rise when multiphoton ionization dominates, while the change rule is inversed when tunnel ionization dominates.
140.7090 Ultrafast lasers 160.5690 Rare-earth-doped materials 220.4000 Microstructure fabrication 320.7110 Ultrafast nonlinear optics High-quality holmium-doped Y 3 Al 5 O 12 (YAG) ceramic is fabricated in sequence by tape-casting and vacuum sintering. The average grain size of the Ho:YAG ceramic is around 20 μm with a fully dense microstructure. The inline transmittance of the sample is ~ 82 % in visible and IR region. The fluorescence lifetime at 2088 nm is 8.17 ms. The excellent properties of the Ho:YAG ceramic demonstrate the tape-casting is a novel candidate process for the fabrication of Ho:YAG-based thin-chip or composite ceramics.
140.3390 Laser materials processing 160.4760 Optical properties 300.2530 Fluorescence, laser-induced Actively tunable metamaterial resonators based on colossal magnetoresistance in the infrared regimeDownload:971次
We present a tunable resonator consisting of a colossal magnetoresistant cross in which a smaller gold cross is embedded. Simulations show the resonance frequencies of the resonator move into the infrared regime when there is a change in the intensity of the external magnetic field applied to the resonator. The source of the tunability is the variance in the colossal magnetoresistance in the resonator when the intensity of the magnetic field changes, which accordingly leads to a shift in the resonance frequency. Such a method offers a new way to achieve tunability, which has potential applications in controllable photoelectric elements.
160.3918 Metamaterials 260.5740 Resonance 050.1755 Computational electromagnetic methods 260.2110 Electromagnetic optics In this work, the absorption, fluorescence spectra, and fluorescence decay curve of Nd : Lu 3 Al 5 O 12 , i.e., neodymium lutetium aluminum garnet (Nd:LuAG) ceramic are investigated. A diode-end-pumped Nd:LuAG ceramic laser is demonstrated for the first time (to our knowledge). We present the experiment results of Nd:LuAG ceramic’s continuous wave (CW) and electro-optically (E-O) Q-switched performance. CW output power of 2.5 W is obtained, corresponding to optical-to-optical efficiency of 17.2% and slope efficiency of 24.3%. For the E-O Q-switched setup, the shortest pulse width and the largest pulse energy are measured to be 4.8 ns and 1.96 mJ, respectively. Its optical-to-optical efficiency and the slope efficiency are 17.3% and 28.7%, respectively.
160.3380 Laser materials 140.3380 Laser materials 140.3480 Lasers, diode-pumped 140.3530 Lasers, neodymium In this work two different fluorochromes (Alexa 594 and Alexa 680) are conjugated to the same monoclonal antibody (Cetuximab) for obtaining a characteristic M-shaped dual-peak spectrum. Dual-labeling of Cetuximab by mixing both fluorochromes before the conjugation step gives spectral results similar to those of mixing of fluorochrome-labeled Cetuximab after the conjugation step ( P > 0.05 ) . In conclusion, both methods may be used equivalently for producing a dual-labeled single-antibody probe. Future studies may test whether the M-shaped spectrum may increase the diagnostic confidence in tumor-targeted multispectral optical imaging.
170.0170 Medical optics and biotechnology 170.3880 Medical and biological imaging 170.4580 Optical diagnostics for medicine Based on the inverse Faraday effect, a super-long longitudinal magnetization needle can be induced by a transversely polarized needle-shaped electric field. This needle-shaped electric field can be obtained in the focal volume of the objective by focusing an azimuthally polarized vortex beam that is modulated both radially and azimuthally by a specifically designed annular phase filter. The numerical calculation shows that the full widths at half-maximums in longitudinal direction and in transverse direction of the magnetization needle are 28 λ and 0.27 λ . The corresponding needle aspect ratio of 103 is more than ten times larger than that of the magnetization needle fabricated by electron beam lithography.
210.3820 Magneto-optical materials 260.5430 Polarization 350.5500 Propagation 060.5060 Phase modulation A model that considers both thermal expansion and thermo-optical effects is developed to investigate the transmission variation of optical coatings when they are exposed to an intense laser beam. Our results indicate that a higher gradient of the transmission spectrum curve at a certain wavelength leads to a more evident variation of the coating transmission. Three customized HfO 2 – SiO 2 multilayer coatings with different transmission spectra are used to measure the transmitted power under the irradiation of a 1080 nm continuous-fiber laser. Excellent agreement is found between the experimental result and the theoretical prediction. Our result is helpful for the improvement of such devices in the application of high-power laser systems.
240.0310 Thin films 310.6188 Spectral properties 动态信息
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