Cr3+/Yb3+ codoped Y3Al5O12 (i.e., YAG) thin films are prepared by pulsed laser deposition. The films are characterized by X-ray diffraction, atomic force microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and photoluminescence spectra. Excitation at 446 or 587 nm, a broadband emission in the range of 610–800 nm, and an intense near-infrared at 1030 nm are obtained, showing cooperative energy transfer from Cr3+ to Yb3+ ions in the Cr3+/Yb3+ codoped YAG thin films; energy transfer efficiency is 71%. The YAG films may have potential application to enhance the efficiency of silicon solar cells.

In order to select a suitable spatial filter for the spatial filtering velocimeter, the filtering characteristics of the spatial filters with a rectangular window and rectangular transmittance are investigated by the power spectrum of transmittance function method. The filtering characteristics of differential filters are investigated and compared with that of common ones. The influences of the number of spatial periods on the spectral bandwidth, deviation to central frequency, and peak transmittance are deeply analyzed. The results show that the influence is due to the form of superposition of the signal components and other components, the pedestal and higher-order components, and the superposition results from the finite size of the spatial filter. According to the results, a method is proposed to compensate for the deviation to central frequency.

Past research has demonstrated that if the intensity image of an object is uniformly down-sampled and converted into a Fresnel hologram, the phase component alone will be sufficient to reconstruct the source image. However, due to down-sampling, the edge and line patterns are degraded heavily. In this Letter, we propose an enhancement on the parent method by incorporating an adaptive down-sampling lattice. A hologram generated with our proposed method, which is referred to as the edge-enhanced sampled phase-only hologram, preserves favorable visual quality on both the shaded regions as well as the edge patterns of the object image.

We demonstrate a new fiber-based radio frequency (RF) dissemination scheme suitable for a star-shaped branching network. Without any phase controls on the RF signals or the use of active feedback-locking components, the highly stable reference frequency signal can be delivered to several remote sites simultaneously and independently. The relative frequency stabilities of 6×10 15/s and 7×10 17/104 s are obtained for a 10 km dissemination. This low cost and scalable method can be applied to a large-scale frequency synchronization network.

A laser-diode-pumped high-pulse-energy Nd:LiYF4 master oscillator power amplifier 1053 nm laser system is demonstrated. We design a home-made pump module to homogenize the pump intensity through the ray tracing method. To increase the extraction efficiency, the pre-amplifier adopts a double-pass amplification structure. At a repetition rate of 50 Hz, 655 mJ pulse energy and 12.9 ns pulse width of 1053 nm laser is obtained from the master oscillator power amplifier system. The corresponding peak power is 51 MW. The optical-to-optical efficiency of the system is about 9.7%.

Metals in nature exhibit a mediocre wettability and a high optical reflectance from the visible region to the infrared. This Letter reports that, by formation of nano- and microscale structures via a simple raster scanning of a focused femtosecond laser pulse without any further treatment, structured aluminum and nickel surfaces exhibit combined features of superhydrophobicity with a contact angle of 155.5°, and a high optical absorption with a reflectivity of several percent over a broad spectral range (0.2–2.5 μm). Thus, a multifunctional structured metal surface that integrates superhydrophobicity and a high broadband absorptivity has been easily realized by one-step femtosecond laser processing.

In laser-arc double-sided welding, the spectral characteristics of the arc plasma are calculated and analyzed by spectroscopic diagnosis. The results show that, compared with conventional tungsten inert gas (TIG) welding, the introduction of a laser changes the physical characteristics of the arc plasma regardless of whether laser plasma penetration takes place, and that the influence of the laser mainly affects the near-anode region of the arc. When the laser power is relatively low, the arc column tends to compress, and the arc spectral characteristics show no significant difference. When the arc root constricts, compared with pure TIG arc, the electron density increases by ～2.7 times and the electron temperature decreases by ～3000 K. When the arc column expands, the intensities of spectral lines of both the metal and Ar atoms are the strongest. But it is also observed that the electron density reduces, whereas there is no obvious decrease of electron temperature.

We report on a widely tunable, narrow linewidth operation of a Tm:YAG ceramic laser. A volume Bragg grating is used in the cavity as a folding mirror for wavelength selection. The wavelength is tuned from 1956.2 to 1995 nm, leading to a total tuning range of 38.7 nm. The linewidth is around 0.1 nm over the whole tuning range. A maximum output power of 1.51 W at 1990.5 nm is achieved at 37.8 W absorbed pump power. Different saturation behaviors are observed in the laser performances at different wavelengths.

In this Letter, we describe an optical assembly that is designed for the engineering application of the atomic laser cooling techniques. Using a folded optical path scheme, we have built a miniaturized, compact magneto-optical trap (CMOT) for an Rb87 atomic fountain clock. Compared with the conventional magneto-optical traps used in other clocks, our system is more robust, more compact, more stable, and saves about 60% laser power. This optical setup has operated for about a year in our fountain system, passed the thermal cycle tests and the mechanical vibration and shock tests, and maintained a high performance without a need for realignment.

All-fiber signal combiner is a key component for augmenting the fiber laser power. Presently the reported 7×1 signal combiners are all have output fibers with core diameters larger than 100 μm. In order to improve the beam quality of the combiner, a fiber with smaller core of 50 μm diameter is chose to be the output fiber. An all-fiber 7×1 signal combiner is fabricated with measured power transmission efficiency around 99% for each port. The beam quality is improved and the measured M2 are around 6 which are matched well with the theoretically calculated results.

Self-Q-switching is observed in a bulk Yb:KGd(WO4)2 oscillator without any additional modulating elements. The output power reaches 434.4 mW at a pump power of 13.67 W, corresponding to pulse repetition rate of 125 kHz and a pulse duration of 2.5 μs, respectively. The mechanism of self-pulse formation is explained by the re-absorption effect of the Yb3+ ion in Yb:KGd(WO4)2.

We propose and experimentally demonstrate a novel scheme to realize electrical/optical (E/O) conversion on the receiver side of a wireless fiber integration system at the W band. At the receiver, a directly modulated laser (DML) is used to realize E/O conversion. The received 85 GHz wireless millimeter-wave (mm-wave) signal is first down-converted into a 10 GHz electrical intermediate-frequency (IF) signal to overcome the insufficient bandwidth of the subsequent DML. Then, two cascaded electrical amplifiers (EAs) are employed to boost the electrical IF signal before it is used to drive a DML. By using this scheme, we transmit a 10 Gb/s 16 quadrature amplitude modulation (16QAM) signal over a 10 m wireless link, and then deliver it over a 2 km single-mode fiber-28 (SMF-28) wire link with a bit error ratio (BER) that is less than the hard-decision forward error correction threshold of 3.8×10 3. Our experimental results show that the DML is good device to be used for the E/O conversion of a 16QAM signal.

Yb-doped silica glasses containing low, medium, and high content of OH are prepared through nanoporous glass sintering technology. High-OH sample exhibits better X-ray irradiation resistivity than low- and medium-OH samples. After irradiation, OH content of low- and medium-OH samples increases 37.5% and 11%, respectively; in contrast, OH content of high-OH sample decreases dramatically. The different OH content changes among the samples are discussed regarding the proposed inter-conversion reactions involving Si-H and Si-OH during the irradiation.

In this work we study all-optical multi-channel return-to-zero (RZ)–on-off keying (OOK) to nonreturn-to-zero (NRZ)–OOK format conversion in single uniform fiber Bragg grating (FBG) for mixed line-rate dense wavelength-division multiplexing systems using mathematical simulations. Forty and 20 Gbit/s RZ–OOK signals with 33% and 50% duty cycles are converted to NRZ–OOK signals in single uniform FBG with 21% reflectivity. Impact of amplitude noise from FBG contrast profile on modulation format conversion efficiency is also studied.

We propose and experimentally demonstrate an ultra-flat optical frequency comb (OFC) generator by a balanced driven dual parallel Mach–Zehnder modulator. Five- and seven-tone OFC with exactly equal intensity can be generated theoretically. Experimentally obtained five- and seven-tone OFC with flatness of 0.6 and 1.26 dB are demonstrated, respectively, which agrees well with the theoretical results.

Light-induced transverse thermoelectric effect is investigated in incline-oriented Bi2Sr2Co2Oy thin films covered with a graphite light absorption layer. Upon the illumination of a 980 nm cw laser, an enhanced voltage signal is detected and the improvement degree is found to be dependent on the thickness of the graphite layer. A two-dimensional (2D) heat transport model using the finite-difference method provides a reasonable explanation to the experimental data. Present results give some valuable instructions for the design of light absorption layers in this type of detector.

The characteristics of stimulated Brillouin scattering (SBS) in perfluorinated amine media and the experimental structure used in hundreds of picoseconds pulse compression at 532 nm are demonstrated. A two-stage SBS pulse compression structure is adopted for this work. The compact double-cell SBS compression structure and the scattering media FC-70 are chosen to compress the incident light from 9.5 to about 1 ns in the first stage. Then, the light is used as the pumping source for the second pulse compression. In the second stage, using a single-cell SBS structure in a pulse compression system, perfluorinated amine media with different phonon lifetimes, such as FC-3283, FC-40, FC-43, and FC-70, are chosen to run the comparative experimental study. The narrowest compressed pulse times obtained are 294, 274, 277, and 194 ps; they respectively correspond to the above listed media. The average width of the compressed pulse width is 320 ps for FC-3283, with a fluctuation range of 87 ps. For FC-40, the average pulse width is 320 ps, with a fluctuation range of 72 ps. And for FC-43, the average pulse width is 335 ps, with a fluctuation range of 88 ps. However, the average pulse width is only 280 ps for FC-70, with a fluctuation range of 57 ps. The highest energy reflectivity is more than 80% for all of the media. The experimental results show that a two-stage SBS pulse compression system has lower pump energy requirements, thus making it easier to achieve a compressed pulse waveform. The results also show that the shorter the phonon lifetime of the medium, the narrower the obtained compressed pulse width.

An interesting transition between low spatial frequency laser-induced periodic surface structure (LIPSS) and high spatial frequency LIPSS (HSFL) on the surface of nickel is revealed by changing the scanning speed and the laser fluence. The experimental results show the proportion of HSFL area in the overall LIPSS (i.e., K) presents a quasi-parabola function trend with the polarization orientation under a femtosecond (fs) laser single-pulse train. Moreover, an obvious fluctuation dependence of K on the pulse delay is observed under a fs laser dual-pulse train. The peak value of the fluctuation is found to be determined by the polarization orientation of the dual-pulse train.

The energy of light exposed on human skin is compulsively limited for safety reasons which affects the power of photoacoustic (PA) signal and its signal-to-noise ratio (SNR) level. Thus, the final reconstructed PA image quality is degraded. This Letter proposes an adaptive multi-sample-based approach to enhance the SNR of PA signals and in addition, detailed information in rebuilt PA images that used to be buried in the noise can be distinguished. Both ex vivo and in vivo experiments are conducted to validate the effectiveness of our proposed method which provides its potential value in clinical trials.

We report a compact 2×2 Mach–Zehnder interferometer (MZI) electro-optic switch fabricated on a silicon-on-insulator using standard complementary metal-oxide semiconductor (CMOS) processes. With a short modulation arm length of 200 μm, the crosstalk is reduced to 22 dB by the new modulation scheme of push–pull modulation with a pre-biased π/2 phase shift. The new modulation scheme can also work with a fast switching time of about 5.4 ns.

A portable infrared spectral radiance measurement apparatus without the cooling based on PbSe detectors is designed to measure the spectral radiance of the object in the wavelength range from 2.1 to 4.1 μm. Cores Luxell 256 module is applied which integrates 256 pixel line array PbSe detectors, amplifiers, analog-to-digital convertors, and Universal Serial Bus output interface. Electric aperture is applied to eliminate the effect of temperature drift. Wavelength and response function of the apparatus is calibrated with the blackbody. Results show that the wavelength resolution is 10 nm. The relative error of measured spectral radiance is below 2.3%.