GaN based ultraviolet laser diodes

In the past few years,many groups have focused on the research and development of GaN-based ultraviolet laser diodes(UV LDs).Great progresses have been achieved even though many challenges exist.In this article,we analyze the challenges of developing GaN-based ultraviolet laser diodes,and the approaches to improve the performance of ultraviolet laser diode are reviewed.With these techniques,room temperature(RT)pulsed oscillation of AlGaN UVA(ultraviolet A)LD has been realized,with a lasing wavelength of 357.9 nm.Combining with the suppression of thermal effect,the high output power of 3.8 W UV LD with a lasing wavelength of 386.5 nm was also fabricated.

An injection-locking diode laser at 671 nm with a wide tuning range up to 6 GHz

We present a compact injection-locking diode laser module to generate 671 nm laser light with a high output power up to 150 m W.The module adopts a master-slave injection-locking scheme,and the injection-locking state is monitored using the transmission spectrum from a Fabry-Perot interferometer.Beat frequency spectrum measurement shows that the injection-locked slave laser has no other frequency components within the 150-MHz detection bandwidth.It is found that without additional electronic feedback,the slave laser can follow the master laser over a wide range of 6 GHz.All the elements of the module are commercially available,which favors fast construction of a complete 671-nm laser system for the preparation of cold^(6)Li atoms with only one research-grade diode laser as the seeding source.

Effect of inhomogeneous broadening on threshold current of GaN-based green laser diodes

The inhomogeneous broadening parameter and the internal loss of green LDs are determined by experiments and theoretical fitting. It is found that the inhomogeneous broadening plays an important role on the threshold current density of green LDs. The green LD with large inhomogeneous broadening even cannot lase. Therefore, reducing inhomogeneous broadening is a key issue to improve the performance of green LDs.

Diode Laser Soldering Technology of Fine Pitch QFP Devices

The laser provides a controllable means of supplying localized energy for solder joint formation and is a valuable tool in electronics manufacture.Diode laser soldering for fine pitch QFP devices were carried out with Sn-Ag-Cu lead-free solder and Sn-Pb solder respectively,and the mechanical properties of micro-joints of the QFP devices were tested and studied by STR-1000 micro-joints tester.The results indicate that sound QFP micro-joints without bridging or solder ball are gained by means of diode laser soldering method with appropriate laser processing parameters,and the pitch of the QFP devices is as fine as to 0.4mm.Tensile strength of QFP micro-joints increases gradually with the increase of laser output power,the maximum tensile strength presents when the laser output power increase to a certain value.The results also indicate that the mechanical properties of QFP micro-joints soldered by diode laser soldering system are better than those of QFP micro-joints soldered by IR reflow soldering method.The experimental results may provide a theory guide for investigation of diode laser soldering.

Effect of microstructure of Au80Sn20 solder on the thermal resistance TO56 packaged GaN-based laser diodes

Au80Sn20 alloy is a widely used solder for laser diode packaging.In this paper,the thermal resistance of Ga N-based blue laser diodes packaged in TO56 cans were measured by the forward voltage method.The microstructures of Au80Sn20 solder were then investigated to understand the reason for the difference in thermal resistance.It was found that the microstructure with a higher content of Au-rich phase in the center of the solder and a lower content of(Au,Ni)Sn phase at the interface of the solder/heat sink resulted in lower thermal resistance.This is attributed to the lower thermal resistance of Au-rich phase and higher thermal resistance of(Au,Ni)Sn phase.

Effect of diode-laser parameters on shear force of micro-joints soldered with Sn-Ag-Cu lead-free solder on Au/Ni/Cu pad

Soldering experiments with Sn-3.5Ag-0.5Cu lead-free solder on Au/Ni/Cu pad were carried out by means of diode-laser and IR reflow soldering methods respectively.The influence of different heating methods as well as output power of diode-laser on shear force of micro-joints was studied and the relationship between the shear force and microstructures of micro-joints was analyzed.The results indicate that the formation of intermetallic compound Ag3Sn is the key factor to affect the shear force and the fine eutectic network structures of micro-joints as well as the dispersion morphology of fine compound Ag3Sn,in which eutectic network band is responsible for the improvement of the shear force of micro-joints soldered with Sn-Ag-Cu lead-free solder.With the increases of output power of diode-laser,the shear force and the microstructures change obviously.The eutectic network structures of micro-joints soldered with diode-laser soldering method are more homogeneous and the grains of Ag3Sn compounds are finer in the range of near optimal output power than those soldered with IR reflow soldering method,so the shear force is also higher than that using IR reflow soldering method.When the output power value of diode-laser is about 41.0 W,the shear force exhibits the highest value that is 70% higher than that using IR reflow soldering method.

Mechanical properties of QFP micro-joints soldered with lead-free solders using diode laser soldering technology

Soldering experiments of quad flat package(QFP) devices were carried out by means of diode laser soldering system with Sn-Ag-Cu and Sn-Cu-Ni lead-free solders, and competitive experiments were also carried out not only with Sn-Pb eutectic solders but also with infrared reflow soldering method. The results indicate that under the conditions of laser continuous scanning mode as well as the fixed laser soldering time, an optimal power exists, while the optimal mechanical properties of QFP micro-joints are gained. Mechanical properties of QFP micro-joints soldered with laser soldering system are better than those of QFP micro-joints soldered with IR reflow soldering method. Fracture morphologies of QFP micro-joints soldered with laser soldering system exhibit the characteristic of tough fracture, and homogeneous and fine dimples appear under the optimal laser output power.

Effect of Droop Phenomenon in InGaN/GaN Blue Laser Diodes on Threshold Current

Electroluminescence （EL） and temperature-dependent photolumineseenee measurements are performed to study the internal quantum efficiency droop phenomenon of blue laser diodes （LDs） before lasing. Based on the ABC mode, the EL result demonstrates that non-radiative recombination rates of LDs with threshold current densities of 4 and 6kA/cm2 are similar, while LD with threshold current density of 4kA/cm2 exhibits a smaller auger- like recombination rate compared with the one of 6kA/cm2. The internal quantum efficiency droop is more serious for LD with higher threshold current density. temperature-dependent photoluminescence is consistent The internal quantum efficiency value estimated from with EL measurements.

Influence of laser intensity in second-harmonic detection with tunable diode laser multi-pass absorption spectroscopy

Tunable diode laser absorption spectroscopy （TDLAS） has been widely employed in atmospheric trace gases detection. The ratio of the second-harmonic signal to the intensity of laser beam incident to the multi-pass cell is proved to be proportional to the product of the path length and the gas concentration under any condition. A new calibration method based on this relation in TDLAS system for the measurement of trace gas concentration is proposed for the first time. The detection limit and the sensitivity of the system are below 110 and 31ppbv （parts-per-billion in volume）, respectively.

Room-temperature continuous-wave operation of GaN-based blue-violet laser diodes with a lifetime longer than 1000h

GaN-based continuous-wave operated blue-violet laser diodes(LDs) with long lifetime are demonstrated, which are grown on a c-plane GaN substrate by metal organic chemical vapor deposition with a 10 × 600 μm^2 ridge waveguide structure.The electrical and optical characteristics of a blue-violet LD are investigated under direct-current injection at room temperature(25 °C). The stimulated emission wavelength and peak optical power of the LD are around 413 nm and over 600 mW, respectively.In addition, the threshold current density and voltage are as small as 1.46 kA/cm^2 and 4.1 V, respectively. Moreover, the lifetime is longer than 1000 hours under room-temperature continuous-wave operation.

LD端面泵浦Tm:SrF_(2)电光调Q激光器

高掺杂浓度的Tm^(3+)增益介质能通过交叉弛豫过程提高激光器的量子效率,但同时也会增加能量上转换带来的损耗,从而限制激光器效率的进一步提升。对Tm:SrF_(2)晶体的荧光特性以及激光性能展开研究。在激光二极管(LD)端面泵浦下,实现最大功率2.99 W的自由运转输出,激光器的泵浦阈值为0.89 W,中心波长1851 nm,斜效率高达82.1%。采用KTP电光调Q开关演示了Tm:SrF_(2)激光器的电光调Q输出特性。在500 Hz重复频率下,获得了1.02 mJ的最大单脉冲能量,泵浦阈值为2.01 W,最短脉冲宽度为45 ns,对应峰值功率为22.67 kW。实验结果表明,基于LD泵浦的Tm:SrF_(2)激光器具有非常高的效率,有望成为中红外光学参量振荡器(OPO)和光学参量放大器(OPA)的理想泵浦源。

A remote sensing system of vehicle emissions based on tunable diode laser technology

As being an effective real-time method of monitoring vehicle emissions on-road, a remote sensing system based on the tunable diode laser （TDL） technology was presented, and the key technologies were discussed. A field test in Guangzhou（Guangdong, China） was performed and was found that the factors, such as slope, instantaneous speed and acceleration, had significant influence on the detectable rate of the system. Based on the results, the proposal choice of testing site was presented.

Experimental Study of Nd^(3+):KGd(WO_(4))_(2) Laser Pumped by Laser Diode

This paper presents the cw output characteristics of Nd^(3+):KGd(WO_(4))_(2)(KGW)laser crystal with different NcP+concentration grown in our laboratory.The laser output at 1.067 μm of KGW crystal(3×3×6 mm)was obtained to be 68.9 mW and the slope efficiency reached 28.8%when pumped by laser diode of power 305 mW at 807 nm.

GaN-based blue laser diode with 6.0 W of output power under continuous-wave operation at room temperature

In this work,we reported the room-temperature continuous-wave operation of 6.0 W GaN-based blue laser diode(LD),and its stimulated emission wavelength is around 442 nm.The GaN-based high power blue LD is grown on a c-plane GaN substrate by metal organic chemical vapor deposition(MOCVD),and the width and length of the ridge waveguide structure are 30 and 1200μm,respectively.The threshold current is about 400 mA,and corresponding threshold current density is 1.1 kA/cm2.

Broad bandwidth interference filter-stabilized external cavity diode laser with narrow linewidth below 100kHz

Interference filter-stabilized external cavity diode lasers （ECDLs） have properties of simple configurations, high sta- bilities, and narrow linewidths. However, the interference filter used in common ECDL designs requires an ultra-narrow bandwidth （about 0.3 nm） to achieve mode selection, that is considerably expensive and not yet available for a wide range of wavelengths. In this paper, a robust ECDL using an available broad bandwidth （about 4 nm） interference filter as the wavelength discriminator is constructed and tested. The ECDL demonstrated a narrow Lorentzian fitted linewidth of 95 kHz and a spectral purity of 2.9 MHz. The long-term frequency stability of the ECDL reaches 5.59 x 10 12.

Diode laser using narrow bandwidth interference filter at 852 nm and its application in Faraday anomalous dispersion optical filter

We demonstrate an 852-nm external cavity diode laser（ECDL） system whose wavelength is mainly determined by an interference filter instead of other wavelength selective elements. The Lorentzian linewidth measured by the heterodyne beating between two identical lasers is 28.3 k Hz. Moreover, we test the application of the ECDL in the Faraday atomic filter.Besides saturated absorption spectrum, the transmission spectrum of the Faraday atomic filter at 852 nm is measured by using the ECDL. This interference filter ECDL method can also be extended to other wavelengths and widen the application range of diode laser.

Arbitrary frequency stabilization of a diode laser based on visual Labview PID VI and sound card output

We report a robust method of directly stabilizing a grating feedback diode laser to an arbitrary frequency in a large range. The error signal, induced from the difference between the frequency measured by a wavelength meter and the preset target frequency, is fed back to the piezoelectric transducer module of the diode laser via a sound card in the computer. A visual Labview procedure is developed to realize a feedback system. In our experiment the frequency drift of the diode laser is reduced to 8 MHz within 25 min. The robust scheme can be adapted to realize the arbitrary frequency stabilization for many other kinds of lasers.

Thermal analysis of GaN laser diodes in a package structure

Using the finite-element method, the thermal resistances of GaN laser diode devices in a TO 56 package for both epi-up configuration and epi-down configuration are calculated. The effects of various parameters on the thermal characteristics are analysed, and the thicknesses of the AlN submount for both epi-up configuration and epi-down configuration are optimized. The obtained result provides a reference for the parameter selection of the package materials.

Ⅲ-nitride based ultraviolet laser diodes

In recent years,because of their small size,high efficiency and environment-friendly advantages,Ⅲ-nitride based ultraviolet(UV)light-emitting diodes(LEDs)have been widely used in many areas to substitute for mercury lamps,such as in 3D printing,curing and sterilization.Ⅲ-nitride alloys cover the whole UV spectrum which is comprised of UV-A(320–400 nm),UV-B(280–320 nm)and UV-C(200–280 nm)by controlling Al/Ga/In content.In addition,Ⅲ-nitride based UV laser diodes(LDs)also have some potential applications in the case of high-power-density,narrow-spectrum,good-directional lighting.However,Ⅲ-nitride based UV laser diodes still have many challenges such as poor crystal quality and low hole concentration in p-type AlGaN.

LD环状侧面均匀泵浦Nd∶YAG激光振荡器

激光二极管(Laser Diode,LD)环状侧面均匀泵浦的激光振荡器具有结构简单、光束质量高、单脉冲能量大等特点,常常在高能脉冲固体激光器中作为主振荡功率放大(MOPA)结构的振荡器,一直是国内外科研人员研究的重要方向之一。本论文通过Zemax软件对不同激光二极管排列方式以及不同工作物质吸收系数对吸收光场的影响的进行了仿真。基于仿真结果,设计了一种20个bar条串联的环状侧面泵浦结构,以提高晶体吸收的均匀性。通过该环状侧泵结构,结合超高斯非稳腔设计,搭建了一种双棒串接激光振荡器进行实验研究。该振荡器实现了在100 Hz重复频率下,单脉冲能量为496 mJ、脉冲宽度为12.4 ns的1064 nm激光输出,光束质量优于9 mm·mrad,光-光转换效率为18.5%。并且该振荡器可以维持光轴稳定不变的同时,实现20 ns脉宽以内变档可调。实验结果证明了该环状侧面均匀泵浦结构可靠有效,为MOPA结构振荡器选取提供了一种有效的方案。