Investigations On Beam And Wavelength Control Of High Power Vertical External Cavity Surface Emitting Semiconductor Laser

Optically pumped vertical-external-cavity surface-emitting lasers(OP-VECSELs),also known as optically pumped semiconductor-disk lasers(OP-SDLs),combine the advantages of optically pumped solid-state lasers and semiconductor lasers,such as good beam quality,high output power,multiple pump-light choices,and no need for doping the epitaxial materials.Nonlinear crystals can be inserted into their unique external cavity for frequency conversion.Combined with a mature semiconductor-band engineering design,VECSELs’ output wavelengths can cover from the ultraviolet to the near-infrared band.At the same time,they can maintain the output beam with a fundamental mode circular symmetric spot at high power output.Single-chip dualwavelength lasing can be achieved by designing the gain-chip structure of VECSELs.The characteristics of low divergence angle and high power density of the laser output from a VECSEL make it suitable for wireless optical power transmission.At transmission distances of several kilometers,the laser beam diameter is only a few tens of centimeters,which can realize long-distance energy transmission.The energy of the monochromatic and high-power-density laser beams can be effectively absorbed and converted into electric energy by the solar cell at the receiver end.The resonant cavity structure of a VECSEL also minimizes the risk of laser leakage.Once any form of obstruction disrupts the laser resonant cavity,the laser oscillation and output will stop immediately.Therefore,using the resonant cavity as the energy transmission path can improve the safety of the wireless laser energy transmission system.VECSELs have been widely used in laser display,gene sequencing,wireless optical power transmission,laser medical and other fields.This paper mainly focuses on the key scientific issues of the gain chip structure,high power output,external cavity beam restriction mechanism and control method of the optically pumped vertical external cavity surface emitting laser,and carries out the research on the beam and wavelength control of the high power vertical external cavity semiconductor laser.The research content and innovative achievements are as follows:(1)Research has been conducted on the high-efficiency frequency doubling of VECSEL.A beam distribution model inside an external resonant cavity was proposed,and a long straight cavity structure was designed for beam control within the cavity.By adjusting the beam waist position with an intra-cavity lens,the frequency doubling crystal was placed near the output mirror to increase the power density of the fundamental frequency light passing through the crystal.An output of 1.258 W of490nm frequency-doubled light was achieved with a 45.57% frequency doubling efficiency when the output power of the 980 nm fundamental frequency light was 2.76 W.(2)Research has been conducted on a single-chip dual-wavelength VECSEL.An active area was constructed using two different In components in the quantum wells,and a micro-cavity control combined with external parameter adjustment was used to achieve emission of two switchable wavelengths on a single chip.The two sets of quantum wells were placed at the corresponding standing wave nodes to achieve effective coupling between the optically generated carriers and photons,and both quantum wells were placed at each other’s standing wave nodes to reduce losses.The designed gain chip can achieve dual-wavelength output with a wavelength spacing exceeding 40 nm.By adjusting the pump power to change the matching relationship between the cavity mode and the gain peak,the switching of dual-wavelength output can be realized.The power output of both wavelengths simultaneously was 250 m W.(3)Aiming at the application of secure wireless optical power transmission,the wireless laser energy transmission system based on VECSEL external resonator structure is studied.The stability parameter analysis model of multi-lens external resonator is established by transfer matrix algorithm.The stable working range of each parameter in the resonator is analyzed according to the stable cavity theory,and the stable resonator structure design is realized.A retroreflector lens system composed of a planar lens and a convex lens is proposed and used as the output end of the laser system.The beam distribution model in the resonant cavity is established,and the beam is regulated by the intracavity lens.It is theoretically proved that the ultra-long laser oscillation cavity with more than 10 m.By constructing an intracavity beam-controlled long straight cavity structure,a long straight cavity VECSEL output with a transmission distance of 1.5 m and an output power of up to 2.58 W is realized.By studying the cavity stability parameters and intra-cavity beam distribution control of VECSEL with long cavity that can deviate from the optical axis output,the maximum output power of705 m W is achieved at a transmission distance of 2 m.Stable laser oscillation can also be maintained when the laser output end deviates from the optical axis by ± 10 mm.