Study On Packaging Technology Of Gain Chip In External Cavity Surface Emitting Lasers

Thermal management technology is a very important part in modern optoelectronics field.Vertical external-cavity surface-emitting lasers（VECSELs）combine the excellent properties of solid-state lasers and semiconductor lasers to obtain high output power and ideal beam quality.And the emission wavelength can be designed according to the actual needs,which has important applications in free space optical communication,nonlinear frequency conversion,laser spectroscopy and other aspects.As with any other kind of laser,the power limitation in VECSELs comes mainly from the thermal effects of the chip.High power VECSELs are usually cooled by bonding the cooling window at the front of the chip or by bonding the heat sink at the rear end.Due to the excellent thermal conductivity of CVD diamond,the thermal conductivity at room temperature is about 2000W/m K,which is five times that of copper.Compared with the traditional copper block heat sink,the use of metallized diamond for heat sink bonding will have better performance.However,diamond has a special lattice structure and does not have suspended chemical bonds on its surface.Under normal conditions,it will not react with any metal or non-metal.Therefore,diamond and gain chip cannot be welded and encapsulated with ordinary solder.In the experiment,titanium at 60nm,platinum at 60nm and gold at 200nm were deposited on the diamond substrate by magnetron sputtering.In the diffusion process,compared with the traditional electron beam evaporation,magnetron sputtering has the advantages of relatively smooth deposited film and stronger adhesion of film.Preliminary results show that while the maximum power output from VECSELs using copper heat sink is0.5W,the maximum power output from diamond heat sink is 1.9W.This means that the diamond heat sink increases the maximum power output from VECESLs by about four times.In this paper,the development and current situation of VECSELs are briefly described,and the advantages of VECSELs compared with traditional solid-state lasers and semiconductor lasers,as well as the different packaging methods and achievements of VECSELs in the domestic and abroad are introduced.Starting from the principle of semiconductor lasers,the paper introduces the luminescence conditions and the basic structure of vertical-external cavity surface-emitting lasers.The structure distribution and reflectivity of distributed Bragg mirrors in VECSELs gain chips and the surface emission characteristics of quantum well are analyzed in detail.Secondly,the thesis introduces the external cavity surface emitting laser packaging of whole process,from the early stage of the chip preparation,cleavage,cleaning,metallization,the selection of heat sink,pretreatment,metal processing,and then to the choice of solder,cleaning,evaporation,by formic acid reduction of welding method,complete external cavity surface emitting laser gain chip encapsulation,at last,by late corrosion substrate etching processing,remove gain chip Ga As substrates,decrease the gain chip thermal resistance at work.The final packaging process was determined by observing and analyzing the surface film of CVD diamond and the output characteristics of the encapsulated external cavity surface emitting laser.Finally,the functions of the optically pumped external cavity surface emitting laser are extended.Cr⁴⁺:YAG crystal and semiconductor saturable absorption mirror SESAM are respectively used as saturable absorption media to obtain stable Q-switched pulse output.When Cr⁴⁺:YAG crystal is used,the width of Q-switched pulse is 10μs,and the pulse repetition frequency is 26.3k Hz.At the same pulse repetition frequency,the width of the Q-modulation pulse obtained by the semiconductor saturable absorption mirror is8μs.Chip based on the external cavity surface emitting laser gain quantum structure,as well as Cr⁴⁺:YAG crystal and semiconductor saturable absorption mirror each time characteristics,and analysis of two different kinds of saturable absorption is discussed under the action of medium,the Q in the external cavity surface emitting laser pulse forming process,preliminary clear this particular kinds of external cavity surface emitting laser in the laser and the Q process related to the physical picture.