Single-lobed Near Diffraction-limited Beam from 1W Laser Diode Array with an External Cavity

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Single-lobed Near Diffraction-limited Beam from 1W Laser Diode Array with an External Cavity

Abstract　An external cavity for the laser diode array with a conventional mirror in what we call two-time self-injection operation is presented. The external cavity consists of two lenses, a flat external mirror(EM) in the image plane of the array and a prism that is used as an output coupler. The single-lobed near diffraction-limited far field beam of a 1 W 10-stripe gain-guided LD array lies at 6.4°～9° with the external cavity operation in two-time self-injection mode, whereas at 2.5°～3.0° for its normal feedback operation. The width of the far field beam (FWHM) is 0.43° and 0.63° at driving current of 2 and 3.2 ×Ithr, respectively, much narrower than that in normal feedback operation, but at the expense of lower output power. The output of the system is very stable and insensitive to the tilt and position of the EM.     

非稳腔傍轴波动方程高斯球面波修正方法的数值研究

在分析用差分方法求解虚共焦非稳腔三维傍轴波动方程,及用数值积分方法与快速付氏变换(FFT)方法求解三维菲涅耳积分方程优缺点的基础上,从激光束在虚共焦非稳腔中以修正高斯球面波形式传输的特征出发,经坐标变换把发散(或会聚)的光束拉直成平行光束,然后用FFT方法求解了在新坐标系中修正函数满足的傍轴波动方程.把相同条件下得到的结果与国内外文献给出的结果进行了比较;计算COIL实验非稳腔给出的近远场结果图象合理正确.     

Continuous-wave operation of a broadly tunable thermoelectrically cooled external cavity quantum-cascade laser

Continuous-wave operation of an external cavity quantum-cascade laser on a thermoelectric cooler is reported. The active region of the gain element was based on a bound-to-continuum design emitting near 5.15 microm. The external cavity setup was arranged in a Littrow configuration. The front facet of the gain chip was antireflection coated. The laser could be tuned over more than 170 cm(-1) from 4.94 to 5.4 microm and was single mode over more than 140 cm(-1). The output power was in excess of 10 mW over approximately 100 cm(-1) and in excess of 5 mW over approximately 130 cm(-1) at -30 degrees C.     

二极管激光阵列在Talbot外腔中同相模的选择

 从理论和实验上对二极管激光阵列在Talbot外腔中的锁相进行了研究。在同相模和异相模近场分布的基础上,利用1维情况下的菲涅耳衍射公式计算了其远场分布。根据同相模和异相模在Talbot腔中的分布特性,采用1/2 Talbot腔并将外腔镜倾斜一个角度a的方法既能选择同相模,又能使模式的功率损耗最小。二极管激光阵列芯片采用CD金刚石材料,“三明治”结构对其进行封装,明显地减小了阵列的“smile”效应。在实验中实现了二极管激光阵列同相模的锁相输出,远场单瓣模的半高全宽为0.11 mm。     

Mode splitting of a cavity with a high-density birefringence rubidium vapor in the superstrong coupling regime

The mode splitting in a system with Doppler-broadened high-density two-level atoms in the presence of magnetic field inside a relatively long optical cavity is studied in the superstrong coupling regime(atoms-cavity coupling strength g√N is near or larger than the cavity free-spectral range?FSR).The effect of a magnetic field applied along the quantization axis is used to break the polarization degeneracy of the cavity and thereby introduce birefringence(or Faraday rotation)into the medium.The cavity modes are further split in the presence of the magnetic field compared with the normal case of the multi-normal-mode splitting of the two-level system near the D2 line of87Rb.The dependence of the mode splitting on the magnetic field and the temperature is studied.The theoretical analysis according to the linear dispersion theory can provide a good explanation.     

Influence of external electric field on the transfer of protons in hydrogen-bonded systems

The LCAO MO self-consistent field method in combination with the 6-31** basis set is used to calculate sections of the potential energy surface for a proton in the NH₃…HCl system in the presence of an external electrostatic field. The field strength is varied in the range of 0.000 to 0.017 a. u. In the absence of the field, the potential of the proton in the isolated complex has one well, the N–Cl distance is equal to 2.92 Å, and the NH₃…H–Cl bond is a hydrogen bond. With increasing distance between the N and Cl atoms, a second well appears in the potential, with the well near the Cl atom remaining deeper. In the presence of an external electric field, with increasing its strength, the depth of the well near the N atom increases, while the height of the barrier for proton transfer from the chlorine to the nitrogen atom decreases. At a certain field strength, the well near the nitrogen atom becomes deeper than that near the chlorine atom, so the proton moves to the nitrogen, making the complex ionic. Thus, the external electric field can influence the type of chemical bond in NH₃…HCl system.     

Probe Response of an Optomechanical System with Optomechanical Coupling Modulated Periodically

In this study, the probe response of a cavity optomechanical system with periodic modulation of the optomechanical coupling is investigated. The modulation arises from the beat effect between two external coherent driving lights, with the beat frequency matching the modulation frequency. The transmission coefficient is derived for the probe field and significant amplification, rather than absorption in the conventional optomechanically induced transparency schemes, is observed near the transparent point when the modulation is introduced. In addition, the coupling modulation can also enhance the slow light effect.     

Magnetic vortices and thermoelectric effect in a hollow superconducting cylinder

The question of a surface barrier which determines the behavior of a vortex in a hollow superconducting cylinder of finite thickness in an external magnetic field is discussed, taking into account magnetic flux quantization in the cavity. The behavior of magnetic vortices in a hollow superconductor in the presence of a thermoelectric current is also considered. Pairs of magnetic vortices with opposite magnetic field orientations (vortex-antivortex pairs) are generated by this current near T _c. The thermoelectric current drives the antivortex (the vortex with oppositely directed field) out of the cylinder, whereas the vortex is ejected into the cavity and remains on the inside cylinder surface as a current. The number of magnetic flux quanta trapped inside the cylinder increases by one. The relation of this mechanism to the “giant” thermoelectric effect in hollow superconductors is discussed. Zh. éksp. Teor. Fiz. 111, 2175–2193 (June 1997)     

利用外腔改善半导体激光器列阵的远场特性

采用一个由快轴准直透镜和一个高反射率平面镜组成的简单外腔,在腔长为几个cm时实现了半导体激光器列阵中部分单元的锁相运行;DLA远场出现了3个瓣,每瓣发散角为10 mrad左右,对比度为50%;通过控制部分单元的输出,可以抑制旁瓣的能量.     

A numerical investigation of the noise radiated by a turbulent flow over a cavity

The tonal noise radiated by a two-dimensional cavity submerged in a low-speed turbulent flow has been investigated computationally using a hybrid scheme that couples numerical flow computations with an implementation of the Ffowcs Williams-Hawkings equation. The turbulent near field is computed by solving the short-time-averaged, thin-layer approximation of the Navier-Stokes equations, with turbulence modelled by the Wilcox k-ω model. Second order spatial and temporal discretization schemes with fine grids in the immediate region of the cavity and a small time step were used to capture the unsteady flow physics. Along all external boundaries, a buffer zone is implemented to absorb propagating disturbances and prevent spurious numerical reflections. Comparisons with experimental data demonstrate good agreement in both the frequency and amplitude of the oscillations within the cavity. The unsteady characteristics of the cavity flow are discussed, together with the mechanisms for cavity noise generation. The influence of freestream flow velocity and boundary layer thickness on the frequency and amplitude of the oscillations within the cavity and the nature of the noise radiated to the far field are also investigated. Results indicate that both the frequency and amplitude of oscillation are sensitively dependent on the characteristics of the shear layer spanning the mouth of the cavity.     

1 W tunable near diffraction limited light from a broad area laser diode in an external cavity with a line width of 1.7 MHz

A novel unstable external cavity for a broad area laser diode is presented. The cavity is based on a V-shaped setup that improves the slow axis beam quality by coupling the internal modes of a gain guided laser diode. The novelty here is the compact unstable resonator design without lenses in direction of the slow axis. For frequency stabilisation and to narrow the line width of the laser diode emission a diffraction grating in a Littrow configuration is used. With this setup up to 1 W of near diffraction limited light with a beam quality of M² ? 1.3 and a line width of 1.7 MHz could be achieved. The external cavity laser was tunable over a range of 35 nm (FWHM) around the center wavelength of 976 nm.     

Generating large steady-state optomechanical entanglement by the action of Casimir force

In this paper,we study an optomechanical device consisting of a Fabry-P′erot cavity with two dielectric nanospheres trapped near the cavity mirrors by an external driving laser.In the condition where the distances between the nanospheres and cavity mirrors are small enough,the Casimir force helps the optomechanical coupling to induce a steady-state optomechanical entanglement of the mechanical and optical modes in a certain regime of parameters.We investigate in detail the dependence of the steadystate optomechanical entanglement on external control parameters of the system,i.e.,the effective detuning,the pump powers of the cavity,the cavity decay rate and the wavelength of the driving field.It is found that the large steady-state optomechanical entanglement,i.e.EN=5.76,can be generated with experimentally feasible parameters,i.e.the pump power P=18.2μW,the cavity decay rateκ=0.5 MHz and the wavelength of the laserλL=1064 nm,which should be checked by optical measurement.     

S波段大间隙速调管放大器输出腔的3维模拟

 利用3维高频软件设计了一种用于S波段大间隙速调管的膜片加载大间隙单重入输出腔,建立了带大耦合孔的输出腔3维全结构模型,采用3维PIC程序对输出腔的提取效果进行了粒子模拟。研究结果表明：膜片加载的大间隙单重入输出腔开大耦合孔后,其所有谐振频点的场分布都不再是TM ₀₁₁模式,因此,在设计此类输出腔时不能以工作频点是否谐振为优化目标。提出了大间隙输出腔设计原则,根据设计原则优化后的输出腔可稳定提取1.07 GW的平均功率,提取效率约35.7%。     

外腔中半导体二极管激光阵列的高阶侧模锁定

 理论分析了外腔较短情况下,宽条半导体二极管激光阵列（LDA）高阶侧模相位锁定的可能性,观察了包含主、旁瓣结构的多侧模远场光强分布。从实验记录结果可以看出,在旁瓣中出现了标志锁相的峰、谷结构,而且该结构的调制度明显高于主瓣中的峰、谷结构的调制度,结果表明：在外腔较短情况下,LDA高阶侧模相位锁定的现象是存在的。     

High power 808 nm vertical cavity surface emitting laser with multi-ring-shaped-aperture structure

The carrier conglomeration effect has been one of the main problems in developing electrically pumped high power vertical cavity surface emitting laser (VCSEL) with large aperture. We demonstrate a high power 808 nm VCSEL with multi-ring-shaped-aperture (MRSA) to weaken the carrier conglomeration effect. Compared with typical VCSEL with single large aperture (SLA), the 300-μm-diameter VCSEL with MRSA has more uniform near field and far field patterns. Moreover, MRSA laser exhibits maximal CW light output power 0.3 W which is about 3 times that of SLA laser. And the maximal wall-plug efficiency of 17.4% is achieved, higher than that of SLA laser by 10%.     

Influences of geometry parameter on mode suppression ratio of fiber grating external cavity semiconductor laser

According to equivalent external cavity approximation model, after taking into account the joint contribution of semiconductor laser, external cavity and fiber grating (FG) to the phase condition, the mode distribution of the fiber grating external cavity semiconductor laser (FGESL) can be determined. As a result, the effect of the FG external cavity length (L) on the side mode suppression ratio (SMSR) of the FGESL is investigated theoretically. The results show that with the injected current and the coupling efficiency increase of the SMSR has taken on rise at all. For strong feedback (R₂ = 10^?4), the SMSR become more flattened with more than 40 dB, but, for weak feedback condition, The SMSR have lesser than 35 dB by an oscillation during rising course. Under the condition of short external cavity, the SMSR is in deep relation to the external cavity length, but the SMSR of longer external cavity is smaller than the SMSR of shorter external cavity on the whole and for 8–11 mm of the external cavity length, the SMSR of the FGESL has better (SMSR > 40.8 dB), and the SMSR become more flattened.     

Experimental and numerical investigation of natural convection of magnetic fluids in a cubic cavity

In this article, natural convections of a magnetic fluid in a cubic cavity under a uniform magnetic field are investigated experimentally and numerically. Results obtained from experiments and numerical simulations reveal that the magnetic field and magnetization are influenced by temperature. There exist relative larger magnetization and magnetic forces in the regions near the upper wall and center inside the cavity than in the region near the bottom and side walls. A weak flow roll occurs inside cavity under the magnetic force, and it brings the low temperature fluid downward in the center region, and streams the high temperature fluid upward along the regions near the sidewalls. With the magnetic field imposed, the heat transfer inside the cavity is enhanced significantly compared to that without the magnetic field, and increasing the strength of the magnetic field the heat transfer is increased further.     

Development of X-Band TE111 Mode ESR Cavity for In Vivo Tooth Dosimetry

Electron spin resonance (ESR) tooth spectroscopy offers the possibility of in vivo dosimetry for radiation accident emergency. We developed an X-band ESR cavity for in vivo measurement of tooth enamel, which is a cylindrical cavity working at TE₁₁₁ mode. A narrow rectangular aperture to fix incisors was opened on the cavity wall, where there were strong microwave magnetic field component H₁ and weak microwave electronic field component E₁ inside the cavity. The external modulated magnetic field was applied to the incisors from both sides of the aperture. Theoretical calculations and simulations were discussed to optimize the characteristics and predict the cavity working conditions and performances. The characteristics were evaluated by measuring DPPH and whole incisor samples. Remarkable radiation induced signal of 2Gy irradiated tooth could be obtained by one 5-min ESR spectroscopy. This result indicated that the cavity was sensitive enough to detect the radiation-induced signal in human teeth. This paper describes the operation principle, configuration, and characteristics, and reports the DPPH and tooth experiments to verify the cavity.     

Quasi-monolithic ring resonator for efficient frequency doubling of an external cavity diode laser

A quasi-monolithic second-harmonic-generation ring resonator assembled with miniaturized components is presented. The ring contains a 10-mm-long bulk periodically poled lithium niobate crystal for second-harmonic generation, four plane mirrors and two gradient-index lenses. All parts are mounted on a glass substrate with an overall size of 19.5 mm×8.5 mm×4 mm. As pump source a broad-area laser diode operated in an external resonator with Littrow arrangement is utilized. This external cavity diode laser provides near diffraction limited, narrow-bandwidth emission with an optical output power of 450 mW at a wavelength of 976 nm. Locking of the diode laser emission to the resonance frequency of the ring cavity was achieved by an optical self-injection locking technique. With this setup more than 126 mW of diffraction-limited blue light at 488 nm could be generated. The opto–optical conversion efficiency was 28% and a wall plug efficiency better than 5.5% could be achieved.