Characteristics of 355 nm Laser Damage in KDP and DKDP Crystals

We present the characteristics of bulk damage induced by the third harmonic of Nd：YAG laser irradiation in KDP and DKDP crystals. Bulk damage occurs as a few or a series of pinpoints consisting of a core and the deforming zone. The results of a 1-on-1 test reveal that the pinpoint size increases with incvreasing fluence, and the pinpoint density increases exponentially with increasing fluence. The results of an s-on-1 test indicate that the pinpoint density increases gradually with laser pulse number, but the size does not grow. These results are consistent with a model in which nanoabsorbers are assumed to exist in the crystal and the initiation of damage is determined by heating them to the critical temperature.

A Novel Ce3＋/Tb3＋ Codoped Phosphate Glass as Down-Shifting Materials for Enhancing Efficiency of Solar Cells

For the purpose of improving conversion efficiency of solar cells by applying the effect of the wavelength conversion of rare earth ions, photo-luminescence and excitation spectrums of Ce3＋-Tb3＋ doped phosphate glass are investigated. Results show that incorporating Ce3＋ ions to Tb3＋-doped phosphate glass can greatly increase the absorption coefficient in the range 300-400 nm and then the energy transfer （ET） from Ce3＋ to Tb3＋ occurs. In addition, increasing Tb3＋ concentration in Ce3＋/Tb3＋ co-doped phosphate glass can greatly enhance the ET efficiency and 545 nm emission intensity. This shows that Ce3＋/Tb3＋ co-doped phosphate glass would be a promising down-shifting material for enhancing the efficiency of solar cells.

Description and reconstruction of one-dimensional photonic crystal by digital signal processing theory

A method of describing one-dimensional photonic crystals （1DPCs） based on Z-domain digital signal processing theory is presented. The analytical expression of the target band gap spectrum in the digital domain is obtained by the autocorrelation of its impulse response. The feasibility of this method is verified by reconstructing two simple 1DPC structures with a target photonic band gap obtained by the traditional transfer matrix method. This method provides an effective approach to function-guided designs of interference-based band gap structures for photonic applications.

High gain optical amplification and lasing performance of the Bi/P co-doped silica fiber in the O-band

In this Letter,the optical amplification characteristics of the home-made Bi/P co-doped silica fiber were systematically explored in the range of 1270–1360 nm.The maximum gain of 24.6 dB was obtained in the single-pass amplification device,and then improved to 38.3 dB in the double-pass amplification device for-30 dBm signal power.In addition,we simultaneously investigated the laser performance of the fiber with the linear cavity.A slope efficiency of 16.4%at~1313 nm was obtained with a maximum output power of about 133 mW under the input pump power of 869 mW at 1240 nm.As far as we know,it is the first laser reported based on the bismuth-doped fiber in China.

Influence of Nd^(3+) concentration on mid-infrared emission in PbF_(2) crystal co-doped with Ho^(3+) and Nd^(3+) ions

A promising series of Ho_(y)Nd_(x)Pb_((1-x-y))F_2(x = 0, 0.01, 0.02, 0.03, 0.04;y = 0.02) crystals was grown by the Bridgman method. The influence of the Nd^(3+)ions concentration on mid-infrared(~2.0, ~2.9 and ~3.9 μm)fluorescence emissions of Ho^(3+)ions in the PbF_(2) crystal excited by 808 nm laser diode was investigated in this work. The energy transfer mechanism between Nd^(3+)ions and Ho~(3+)ions under different concentrations of the Nd^(3+)ions was systematically analyzed. The results show that the Nd^(3+)ions have good sensitization and deactivation effect on the Ho^(3+)ions to stimulate the mid-infrared fluorescence emissions. The experimental analysis proves that the sensitization efficiency of the Nd^(3+)ions is relatively stable at around 93.45% with varying Nd^(3+)-doping concentrations. Concentration dependence studies indicate that the concentration of the Nd^(3+)ions has significant influence on mid-infrared emissions.When the doping concentration of the Nd^(3+)ions is up to 2.0 at%, the intensity of ~2.0, ~2.9 and ~3.9 μm emissions all reach the maximum. The output characteristics of a 3.9 μm laser are simulated, and it is found that with the increase of the Nd^(3+)-doping concentration, the peak power, pulse width, and peak energy all meet the trend of first increasing and then decreasing, and Ho_(0.02)Nd_(0.02)Pb_(0.96)F_(2) crystal displays the best performance. All the results show that the Nd^(3+)/Ho^(3+)co-doped PbF_(2) crystals might act as a useful optical medium for mid-infrared laser applications.

Damage characteristics of fused silica under low-temporal coherence light

The damage characteristics of fused silica were investigated under low-temporal coherence light(LTCL).It was found that the laser-induced damage threshold(LIDT)of fused silica for the LTCL was lower than that of the single longitudinal mode pulse laser,and for the LTCLs,the LIDTs decrease with the increasing of laser bandwidth,which is not consistent with the temporal spike intensity.This is due to the nonlinear self-focusing effect and multi-pulse accumulation effect.The specific reasons were analyzed based on theoretical simulation and experimental study.This research work is helpful and of great significance for the construction of high-power LTCL devices.

Laser-conditioning mechanism of ZrO_2/SiO_2 HR films with fitting damage probability curves of laser-induced damage

The method of fitting damage probability curves of laser-induced damage is introduced to investigate the laser-conditioning mechanism of ZrO2/SiO2 high reflection（HR） films.The laser-induced damage thresholds（LIDTs） of the sample are tested before and after the laser-conditioning scanning process.The parameters of the defects are obtained through the fitting process of the damage probability curve.It can be concluded that the roles of laser conditioning include two aspects：removing defects with lower threshold and producing new defects with higher threshold.The effect of laser conditioning is dependent on the competition of these two aspects.

Gain and laser performance of heavily Er-doped silica fiber fabricated by MCVD combined with the sol-gel method

In this work, a heavily Er-doped fiber with an 8 μm core diameter and a numerical aperture of 0.13 was prepared by the modified chemical vapor deposition(MCVD) technique combined with the sol-gel method. The background loss and absorption coefficient at 1530 nm were measured to be 20 d B/km and 128 d B/m, respectively. Thanks to the sol-gel method, the fiber showed a good doping homogeneity, which was confirmed through unsaturable absorption measurement. The net gains of three 25, 45, and 75-cm-long fibers were measured in the range of 1520 to 1600 nm, and the highest gain reached above 23 d B at both 1530 and 1560 nm in 25 and 75-cm-long fibers, respectively. The short-cavity laser performance was measured using centimeter-scale fibers. The maximum output power of 12 m W was demonstrated in a 6.5-cm-long active fiber with a slope efficiency of 20.4%. Overall, the prepared heavily Er-doped silica fiber is a promising item to be applied in a high-repetition-rate or single-frequency fiber laser.

Spectral properties and laser performance of Nd:Lu_3Al_5O_(12) ceramic

In this work, the absorption, fluorescence spectra, and fluorescence decay curve of Nd：Lu3Al5O12, i.e., neodym- ium 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 ceramics 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 measm-ed 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.

Preparation of high performance thin-film polarizers

The optical performance of thin film polarizers is highly sensitive to the layer thicknesses of thin film.The thicknesses of the sensitive layers are optimized in order to gain broader polarizing zone in such case when the total layer thickness does not increase.An automatic layer thickness control system is established,and errors caused by different monitoring methods are analyzed.With this thickness control system,thin-film polarizers with Tp higher than 98%and Tp/Ts higher than 200：1（Tp and Ts are transmissions for p- and s-polarizations,respectively） with the bandwidth of 11 nm are prepared.Using the system allows for optimum repeatability of three successive runs.

Influence of laser conditioning on defects of HfO_2 monolayer films

The influence of laser conditioning on defects of HfO2 monolayer films prepared by electron beam evaporation （EBE） is investigated utilizing the spot-size effect of the laser-induced damage.It is found that the laser-induced damage threshold of HfO2 monolayer films can be increased by a factor of 1.3-1.6.It is also found that the defects with low threshold can be removed by laser conditioning and defects with higher threshold may be removed partially.

Polarization readout analysis for multilevel phase change recording by crystallization degree modulation

Four different states of Si15Sb85 and Ge2Sb2Te5 phase change memory thin films are obtained by crystallization degree modulation through laser initialization at different powers or annealing at different temperatures. The polarization characteristics of these two four-level phase change recording media are analyzed systematically. A simple and effective readout scheme is then proposed, and the readout signal is numerically simulated. The results show that a high-contrast polarization readout can be obtained in an extensive wavelength range for the four-level phase change recording media using common phase change materials. This study will help in-depth understanding of the physical mechanisms and provide technical approaches to multilevel phase change recording.

Watt-level continuous-wave and passively Q-switched red lasers pumped by a single blue laser diode

Praseodymium-ion-doped gain materials have the superiority of lasing at various visible wavelengths directly.Simple and compact visible lasers are booming with the development of blue laser diodes in recent years.In this Letter, we demonstrate the watt-level red laser with a single blue laser diode and Pr:YLiF4 crystal.On this basis,the passively Q-switched pulse lasers are obtained with monolayer graphene and Co:ZnO thin film as the Q-switchers in the visible range.

High gain E-band amplification based on the low loss Bi/P co-doped silica fiber

A home-made low loss Bi/P co-doped silica fiber was fabricated using the modified chemical vapor deposition(MCVD)technique combined with the solution doping method,where the background loss at 1550 nm was as low as 17 dB/km.We demonstrated for the first time,to the best of our knowledge,an all-fiber amplifier using the home-made Bi/P co-doped fiber achieving broadband amplification in the E-band.The amplifying performance was evaluated and optimized with different pumping patterns and fiber length.A maximum net gain at 1355 nm close to 20 dB and a minimum noise figure of 4.6 dB were obtained for the first time,to the best of our knowledge,using two 1240 nm laser diodes under bidirectional pumping with the input pump and signal powers of 870 mW and−30 dBm,respectively.

Phase-selective fluorescence of doped Ge_2Sb_2Te_5 phase-change memory thin films

In this Letter, new concepts of fluorescence phase-change materials and fluorescence phase-change multilevel recording are proposed. High-contrast fluorescence between the amorphous and crystalline states is achieved in nickel- or bismuth-doped Ge;Sb;Te;phase-change memory thin films. Opposite phase-selective fluorescence effects are observed when different doping ions are used. The fluorescence intensity is sensitive to the crystallization degree of the films. This characteristic can be applied in reconfigurable multi-state memory and other logic devices. It also has likely applications in display and data visualization.

Measuring the topological charge of optical vortices with a single plate

Measuring the topological charge(TC) of optical vortex beams by the edge-diffraction pattern of a single plate is proposed and demonstrated. The diffraction fringes can keep well discernible in a wide three-dimensional range in this method. The redundant fringes of the diffracted fork-shaped pattern in the near-field can determine the TC value, and the orientation of the fork tells the handedness of the vortex. The plate can be opaque or translucent, and the requirement of the translucent plate for TC measurement is analyzed. Measurement of TCs up to ±40 is experimentally demonstrated by subtracting the upper and lower fringe numbers with respect to the center of the light. The plate is easy to get, and this feasible measurement can bring great convenience and efficiency for researchers.

Angle amplifier in a 2D beam scanning system based on peristrophic multiplexed volume Bragg gratings

In this paper,a 2D angle amplifier based on peristrophic multiplexed volume Bragg gratings is designed and prepared,in which a calculation method is firstly proposed to optimize the number of channels to a minimum.The induction of peristrophic multiplexing reduces the performance difference in one bulk of the grating,whereas there is no need to deliberately optimize the fabrication process.It is revealed that a discrete 2D angle deflection range of±30°is obtained and the relative diffraction efficiency of all the grating channels reaches more than 55%with a root-meansquare deviation of less than 3.4%in the same grating.The deviation of the Bragg incidence and exit angles from the expected values is less than 0.07°.It is believed that the proposed 2D angle amplifier has the potential to realize high-performance and large-angle beam steering in high-power laser beam scanning systems.

Energy transfer between Gd^(3+) and Tb^(3+) in phosphate glass

The phosphate glass doped with Gd^3＋, Tb^3＋ and Gd^3＋/Tb^3＋ were prepared by high temperature melting. The photo-luminescence behavior of Gd^3＋ and Tb^3＋ in phosphate glass were investigated by absorption, excitation, and emission spectroscopy. Energy transfer between Gd3＋ and Tb3＋ in phosphate glass was studied, and it was found that there were two energy transfer mechanisms between Gd3＋ and Tb3＋ in phosphate glass： one was from 4f7 level of Gd3＋ to the 4f8 level of Tb3＋, and the other was from 5d level of Tb^3＋to 4f^7 level of Gd^3＋. The new findings would be beneficial for the study of Tb^3＋-doped scintillating phosphate glass.