We experimentally demonstrate N2+ 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 B2Σu+(v′=5,4,3)→X2Σg+(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 N2+ lasing at these wavelengths.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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 <0.556×1014 W/cm2 at which multiphoton ionization dominates, while it fades away when laser intensity >0.556×1014 W/cm2 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.

High-quality holmium-doped Y3Al5O12 (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.

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.

In this work, the absorption, fluorescence spectra, and fluorescence decay curve of Nd:Lu3Al5O12, 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.

Pr3+/Yb3+ co-doped CaNb2O6 thin films are deposited on Si(100) substrates by pulsed laser deposition and annealed at different temperatures in air atmosphere. X-ray diffraction, Raman spectroscopy, atomic force microscopy, X-ray photoelectron spectroscopy, and photoluminescence spectra are used to characterize the samples. The results show that the annealing temperature has a strong effect on the film’s grain size, structure, morphology, and the up-conversion luminescence properties. The grain size and up-conversion luminescence of Pr3+/Yb3+ co-doped CaNb2O6 films increases with the increasing annealing temperature.

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 28λ and 0.27λ. The corresponding needle aspect ratio of 103 is more than ten times larger than that of the magnetization needle fabricated by electron beam lithography.

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 HfO2–SiO2 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.