| With picosecond or femtosecond pulse width,high pulse repetition frequency,wide spectrum and high peak power,the gigahertz(GHz)ultra-short pulse is widely used in many fields such as laser spectroscopy,biomedical applications,optical communication and large-capacity communication systems.Since the invention of Semiconductor Saturable Absorber Mirror,its compactness and low cost make it widely used in femtosecond and picosecond mode-locked lasers.Vertical external cavity surface emitting laser is a new type of laser with the advantages of both semiconductor laser and solid laser.Its pumping absorption efficiency is high,output power is large and the beam quality is good,it can obtain high quality near diffraction limit group transverse mode,as well as its semiconductor gain medium allows flexible design of emission wavelength from visible light to near infrared through band engineering.The flexible external cavity allows other optical elements to be inserted into the cavity for nonlinear frequency conversion,and a semiconductor saturable absorber mirror can be placed in the cavity for passive mode locking to obtain ultra-short laser pulse output.This paper briefly describes the development history and research significance of the vertical external cavity surface emitting laser,summarizes the advantages of the vertical external cavity surface emitting laser and the application of the passive mode-locked external cavity surface emitting laser.Firstly,based on the energy band structure of semiconductor materials,the luminescence principle of semiconductor laser and the basic structure of vertical external cavity surface emitting laser are introduced.The structure and reflectivity of Bragg reflector in VECSEL gain chip and the surface emission characteristics of quantum well are also analyzed in detail.Secondly,the principle of mode locking technology is summarized and the characteristics of passive mode locking with semiconductor saturable absorber mirror are studied.The epitaxial growth,design structure and thermal sink bonding mode of the gain chip of the passive mode-locked vertical external cavity surface emitting laser are studied in detail.In this paper,two bonding ways of Si C thermal sink liquid capillary bonding and metallized diamond bonding are compared,and finally the metallized diamond bonding mode is selected to obtain higher output power.After the bonding of the gain chip,the Ga As substrate was successfully removed by the combination wet and acid etching,which reduced the thermal resistance of the gain chip.The linear cavity structure of the passively Q-switched and mode-locked vertical external cavity surface-emitting laser is built,and the experimental study on the passive Q-switched and mode-locked external cavity surface emitting laser using Cr:YAG crystal is carried out,and output characteristics of the laser are obtained.In the experiment,a linear cavity structure without Cr:YAG was firstly obtained.When the room temperature was 25? and the heat sink temperature was 17?,the pump power was 12 W and the maximum average output power of the laser was 10.4mw.When the pump is larger than 12 W,when Q-switched occurs,and the result of Laser output with the pulse width of 1ms and the repetition frequency of about 263 Hz is obtained.The V cavity structure of the passive mode-locked vertical external cavity surface emitting laser is built,and the experimental study on the passive mode-locked external cavity surface emitting laser is carried out,and the partial gain chip characteristics are obtained.The experiment first obtained the structure of an unused SESAM V cavity with a heat sink temperature of 17?,a pump absorption power of about 10 W,and a resonant cavity of about the same arm length to obtain the highest continuous light output power of up to 0.7W when the laser wavelength is 983 nm.With SESAM locking,the heat sink temperature was 17?,the pump absorption power was 12 W,the length of the straight cavity was 175 mm,and the length of the folded cavity was 29 mm.In this paper,the function of VECSEL is extended,and the dual wavelength VECSEL and miniaturized tunable VECSEL green laser are realized.The dual wavelength output with wavelength space of 147 nm and the green output with tuning range of 4nm are obtained. |
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