Orthogonal linear polarized lasers (II)--Study on the physical phenomena

The physical phenomena and corresponding theoretical analysis of orthogonal polarized laser are reviewed. Four lasers (or systems) with orthogonal polarized beams are involved. For the birefringence dual frequency laser, its physical phenomena discussed include the alternation between strong mode competition and medium mode competition in cavity tuning; the range of frequency difference of strong mode competition (about 0?40 MHz); four polarization statuses (o-light oscillating but e-light extinguishing, both o-light and e-light oscillating, e-light oscillating but o-light extinguishing, both o-light and e-light extinguishing) in cavity tuning; the tuning curves of frequency difference; the influence of optical activity of quartz crystal on polarization direction; and the aberrance of frequency splitting. For the Birefringence-Zeeman dual frequency laser, we focus on its intensity tuning and frequency difference tuning. For the feedback system of orthogonally polarized laser, we discuss the mutual suppression between two orthogonal frequencies, intensity exchange between two orthogonal frequencies and double of intensity fringe frequency. For orthogonally polarized LD-pumped Nd: YAG microchip laser, its property of the dependence of intensity sensitivity on frequency difference is described.     

Orthogonal linear polarized lasers(III) --Applications in self-sensing

In this paper, the applications of orthogonal linear polarized lasers in self-sensing are reviewed. The properties for such a laser include the production of a new frequency in one longitudinal mode spacing, the tuning of frequency difference, the change of polarization states as cavity tuning, the control of mode competition intensity, the optical feedback, and so on. The orthogonal polarized lasers have been used as a laser nanometer ruler based on competition between two polarized lights in a HeNe laser and as a displacement measurement tool based on the optical feedback in the orthogonal polarized lasers. They are also used in the phase retardation measurement of a waveplate, the angle measurement, the vibration measurement, the pressure/force measurement, the weak magnetic field measurement, and so on. The structures of these new devices are simple and compact with the great advantages of high resolution and high accuracy. Some of these devices can trace to the source of the laser wavelength. The nanometer laser ruler is an example whose measurement range is 12 mm, resolution is 79 nm and linearity is less than 5×10^-5. The repeatability of the phase retardation measuring system of waveplate can reach 3′.     

Orthogonal linear polarized lasers (Ⅲ)——Applications in self-sensing

In this paper, the applications of orthogonal linear polarized lasers in self-sensing are reviewed. The properties for such a laser include the production of a new frequency in one longitudinal mode spacing, the tuning of frequency difference, the change of polarization states as cavity tuning, the control of mode competition intensity, the optical feedback, and so on. The orthogonal polarized lasers have been used as a laser nanometer ruler based on competition between two polarized lights in a HeNe laser and as a displacement measurement tool based on the optical feedback in the orthogonal polarized lasers. They are also used in the phase retardation measurement of a waveplate, the angle measurement, the vibration measurement, the pressure/force measurement, the weak magnetic field measurement, and so on. The structures of these new devices are simple and compact with the great advantages of high resolution and high accuracy. Some of these devices can trace to the source of the laser wavelength. The nanometer laser ruler is an example whose measurement range is 12 mm, resolution is 79 nm and linearity is less than 5×10-5. The repeatability of the phase retardation measuring system of waveplate can reach 3'.     

Deformation Behaviors of Laser Forming of Ring Sheet Metals

Laser forming is a highly flexible sheet metal forming technique. In laser forming along curved irradiation paths, the heated zone is bigger and the effects of the processing parameters on the deformation are complex. The deformation behaviors of laser forming of ring sheet metals have been investigated from the thermal-mechanics analysis by the finite element (FE) simulation based on the proposed finite element method model. The effects of ring central angle and scanning path on deformation of ring sheet metal were investigated. The results are as follows: (1) in comparison with the laser bending along linear path, the marked third point has two peak temperatures during the laser forming process along curved path; (2) the forming process fluctutes continuously and the sheet edge is warped because the rigid-ends effect due to the restriction of sheet; (3) when the ring central angle increases, the displacement difference of the marked three points decreases and then increases, and the warped curvature of sheet edge decreases; (4) when the laser beam diameter increases, the displacement difference of the marked three points decreases and the warped curvature increases.     

Polarization-dependent difference of the power spectra from two-dimensional random media with different shapes

Polarization-dependent difference of the power spectra from a set of two-dimensional （2D） passive random media is investigated by simultaneously solving Maxwell＇s equations for both transverse magnetic （TM） and transverse electric （TE） fields. The random media have the same random constitution but different shapes. Results show that both two polarized states are morphology dependent, and the variety of the shapes has more influence on the selection of TM polarized modes than that of TE polarized modes. Such polarization-dependent difference of morphology property presents a new modeselecting technique for random lasers.     

Compact packaging for multi-wavelength DML TOSA

A compact multi-wavelength hybrid-integrated directly-modulated distributed-feedback laser （DML） transmitter optical sub-assembly （TOSA） has been achieved in our laboratory. The 8-channel distributed feedback （DFB） lasers are monolithically integrated based on the reconstruction-equivalent-chirp （REC） technology. With the high-density and high-speed packaging technique, the laser array and a multi-mode interference （MMI） multiplexer are assembled in the TOSA. The channel spacing of the TOSA is 200 GHz between adjacent lasers. It meets the 8 ; 12.5 Gb/s operation demand and gives rather low channel crosstalk of less than -25 dB. This compact TOSA is of effective cost and shows good sta- bility for mass production, which is expected to improve the performance of devices in access networks, data centers and supercomputing.     

Frequency invariant beamforming via jointly optimizing spatial and frequency responses

An approach to designing broadband frequency invariant beamformer based on finite impulse response (FIR) filters via jointly optimizing the spatial and frequency responses is proposed. The beam responses are jointly optimized to satisfy both spatial and frequency domain specifications by designing a bank of FIR filters corresponding to the input channels. It minimizes the maximum error between the designed beam pattern and the desired one in the mainlobe area over the working frequency band, and guarantees the sidelobes in the passband and the beam magnitude responses in the stopband to be below some given threshold values. White noise gain constraint is used to improve the robustness of the beamformer against random errors. The beam patterns are expressed as a linear function of FIR filter impulse responses, and the design problem is formulated as the second-order cone programming (SOCP), which can be solved efficiently via the well-established interior point methods. Results of computer simulation and lake-experiment for a twelve-element semicircular array demonstrate superior performance of this approach in comparison to the existing approaches.     

Emission characteristics of surface second-order metal grating distributed feedback semiconductor lasers

To obtain high-power semiconductor lasers with stable operation in a single longitudinal mode and improve the characteristics of the output beam,an end-emitting surface second-order metal grating distributed feedback(DFB) laser emitting at around 940 nm is fabricated.The characteristics of the uncoated devices with and without gratings are tested under room temperature continuous-wave conditions without any temperature-control device and compared.The devices with gratings achieve high powers of up to 385 mW/facet and a small lateral far-field angle of 2.7° at 1.5 A,have only 4.13 nm/A wavelength-shift,and 0.09 nm spectral linewidth at 600 mA,and operate in a stable longitudinal mode.Devices without gratings operate in multimode,with a larger lateral far-field angle(7.3°) and spectral linewidth(1.3 nm),although with higher output powers.Because of the integration of second-order metal gratings and their very high coupling capability,the output beam quality is improved greatly,the lasing wavelength is stable and varies slowly with changes in injection current,while the spectrum is narrowed dramatically,and the far-field angles are greatly reduced.This opens the way for the realization of watt-scale power broad-stripe(>100 μm) surface second-order metal grating end and surface-emitting DFB lasers and arrays with single frequency,single mode operation and high output beam quality.     

Predictability of Plastic Parts Behaviour Made from Rapid Manufacturing

One of the most important issues to resolve in parts manufactured from rapid manufacturing (RM) technologies is to know their behavior working under real conditions. Total quality manufacturing (TQM) is only possible if mechanical properties are well known in the design stage depending on the processing parameters. This work is mainly focused on testing of several samples made with different selective laser sintering (SLS) parameters and technologies. This procedure is the starting point to establish a basis for designing for RM and the standardization of RM testing. The experiments and the analysis of variance (ANOVA) analyzed the effects of several factors on mechanical properties. The SLS technologies were 3DSystem and EOS. The results show which factor has a large effect on the variables and the interaction between them. The conclusions are very useful for developing rules for designing (designing for RM) and creating new standard rules (ISO, AISI, and DIN) for RM materials and parts testing. The ANOVA gives a better knowledge of the effects of these factors and eliminates unimportant parameters.     

Laser-field-induced magnon amplification in a magnetic semiconductor quantum well under an external magnetic field

The laser-field induced magnon amplification in a magnetic semiconductor quantum well under an external magnetic field was discussed, it is shown that when the laser frequency is near to the electron cyclotron frequency, no matter how weaker the laser field is, the magnon amplification always occurs. In case of fixed laser frequency, the optical absorption of magnons obeys the definite selection rule to the laser field strength. The rate of change of magnon occupation is calculated, and the amplification condition is given.     

Evaluation of ablation differences in air and water for hard tissues using full-field optical coherence microscopy

To clarify the role of a natural or artificial liquid environment in the free-running infrared pulsed laser ablation of hard biological tissues,two-and three-dimensional morphologies of laser-induced craters must be quantitatively measured to distinguish ablation differences in air and in water.Full-field optical coherence microscopy is introduced,which has non-contact,non-destructive,non-preprocessing and higher-resolution advantages.Experimental results indicate that the ablation performances in air and in water are comparable for few laser pulses,but the ablation difference becomes obvious for more laser pulses.Optical coherence microscopy is more feasible than conventional means for the morphological measurement of craters.     

Dissociation of NO2 in femtosecond intense fields

The study of molecules in strong laser fields is a challenging topic in molecular science[1―10]. With the advent of short-pulse lasers, the behavior of molecules can be explored on the time scale of vibrational mo-tions. An intense and linearly polarized…     

Optical frequency standard based on a single 40Ca+

Research on the development of the optical frequency standard based on trapped and cold 40 Ca+ with the 4s2S1/2-3d2D5/2 clock transition at 729nm is reported. A single calcium ion was trapped and laser cooled in the Paul trap and stay in trap for more than 15 days. The linewidth of a 729nm laser was reduced to less than 10Hz by locking to a cavity for longer than 50 hours uninterruptedly. The overall systematic uncertainty of the clock transition has been characterized to be better than 6.5×10 16 . The absolute frequency of the clock transition was measured at 10 15 level using an optical frequency comb referenced to a Hydrogen maser, which was calibrated to the SI second through the global positioning system (GPS). The frequency value was 411042129776393.0(1.6)Hz after the correction of the systematic shifts.     

Study of rapid transient explosive boiling under short-pulsed laser heating

Using acetone, ethanol, water and acetone-water mixture as test liquids, the rapid transient explosive boiling (RTEB) taking place under short-pulsed laser heating is observed in experiment. The behaviors of temperature variation are investigated via transient temperature measurement. The vapor bubble behaviors of RTEB are captured by high-speed photography, and the difference between RTEB and normal boiling is analyzed. The boiling heat transfer of RTEB is also discussed. It shows that the character of RTEB is far different from normal boiling.     

Frequency dependence of magnetization and giant magneto impedance effect of amorphous wires

The frequency dependence of magnetization process and giant magneto impedance (GMI) effect of Co-rich melt-extracted amorphous wires was studied by Kerr effect and impedance analyzer, respectively. It is demonstrated that the transverse Kerr intensity and the corresponding GMI response increase with increasing frequency, which contributes to the upgraded skin effect. However, the skin depth has a slothful trend with frequency when it is up to the megahertz range, which gives rise to the transformation of magnetization. The process is much more sensitive to the direct current magnetic field and the sensitive change of the circular permeability, and GMI response is observed as its consequence. This proves that the evolution of circumferential magnetization and the corresponding permeability with the direct current magnetic field is the essence of GMI response, and a much more sensitive magnetization promises a better GMI response.     

Selective flotation separation of andalusite and quartz and its mechanism

The separation of andalusite and quartz was investigated in the sodium oleate flotation system, and its mechanism was studied by solution chemical calculation, zeta-potential tests, Fourier transform infrared spectroscopic (FTIR), and X-ray photoelectron spectroscopic (XPS). The flotation tests results show that FeCl₃·6H₂O has a strong activation effect on andalusite and quartz and citric acid has a strong inhibitory effect on activated quartz, thus increasing the floatability difference between quartz and andalusite when the pulp pH is approximately 8. The FTIR, Zeta potential, and XPS analyses combined with the chemical calculation of flotation reagent solutions demonstrate that Fe forms hydroxide precipitates on the surface of andalusite and quartz and that oleate anions and metal ions adsorb onto the surface of the minerals. The elements Al and Fe can be chemically reacted. The anions in citric acid have different degrees of dissolution of Fe on the andalusite and quartz surfaces, thereby selectively eliminating the activation of the elemental Fe on andalusite and quartz and increasing the floatability of andalusite, leading to a better separation effect between andalusite and quartz.     

Top-gated graphene field-effect transistors on SiC substrates

We report on a demonstration of top-gated graphene field-effect transistors(FETs) fabricated on epitaxial SiC substrate.Composite stacks,benzocyclobutene and atomic layer deposition Al2O3,are used as the gate dielectrics to maintain intrinsic carrier mobility of graphene.All graphene FETs exhibit n-type transistor characteristics and the drain current is nearly linear dependence on gate and drain voltages.Despite a low field-effect mobility of 40 cm2/(V s),a maximum cutoff frequency of 4.6 GHz and a maximum oscillation frequency of 1.5 GHz were obtained for the graphene devices with a gate length of 1 μm.     

Overall optimization of high-speed semiconductor laser modules

Based on the high frequency techniques such as frequency response measurement, equivalent circuit modeling and packaging parasitics compensation, a comprehensive optimization method for packaging high-speed semiconductor laser module is presented in this paper. The experiments show that the small-signal magnitude frequency response of the TO packaged laser module is superior to that of laser diode in frequencies, and the in-band flatness and the phase-frequency linearity are also improved significantly.     

Harmonic synchronization model of the mating dengue vector mosquitoes

When two mosquitoes meet to mate, each modulates its flight tones such that the female’s 3rd and the male’s 2nd harmonic frequencies are equivalent. We show that this phenomenon is an example of synchronization, which is common in nature. The mosquito’s flight tone acts as an external signal, stimulating its partner to adjust the wing beat rhythm to achieve the synchronization state. A simplified model, which is based on the frequency ratio difference feedback mechanism, is proposed to describe the harmonic convergence of mosquitoes. Furthermore, we proposed a method to characterize the energy dissipation in the frequency alteration, and the results demonstrate that 3/2 frequency locking is an optimal selection to mosquitoes. When compared with other possible ratios, the mosquitoes expend minimum energy if they lock the synchronizing state at a ratio of 3/2.