| It has been 61 years since the invention of the laser.During these decades,the laser has gradually developed into an indispensable part of our lives.Nowadays,lasers can be seen everywhere in our lives,from the laser pointers held by the children under the stars to the igniters of the Shenzhou spacecraft;from the laser cutting machine in the factory to the laser rangefinder for measuring the height of Mount Everest,People enjoy the innovation brought about by the development of laser.Due to the characteristics of high peak power and low thermal effect,pulsed lasers are used in various fields such as metal processing,biomedicine,surveying and mapping.Q-switched technology is one of the methods to generate pulsed lasers.Compared with other types of pulsed lasers,Q-switched lasers have the advantages of easy construction,large single pulse energy,simple and compact structure,and low cost,so they are more widely used.According to whether an external driving source is needed or not,Q-switching can be divided into two forms:active and passive.Active Q-switching is generally realized by adding an acousto-optic modulator or electro-optic modulator in the cavity.The disadvantage is that it is large in size and consumes a lot of power.Passive Q-switching only needs to place an absorber that can control the loss in the cavity to achieve Qswitching output.The most widely used saturable absorber is the semiconductor saturation absorption mirror(SESAM),but its production is very complicated,requires the growth of multiple layers of materials,and the cost is high.People are beginning to look for alternative products.In the 1990s,Chinese researchers discovered that Cr4+:YAG crystal has nonlinear absorption characteristics.The Cr4+:YAG crystal has good performance and high damage threshold,which is very suitable for building Q-switched lasers.Now it has developed into a mature saturable absorption device.In the 21 st century,carbon nanotubes(CNT),graphene,transition metal carbonitrides(MXenes),transition metal dichalcogenides(TMD),black phosphorus(BP)and a series of two-dimensional materials have been found to have saturable absorption characteristics.These new broadband two-dimensional material saturable absorbers are simple to prepare,low in cost,and have a large modulation wavelength range.In recent years,they have attracted more and more attention from researchers.The research content of this article includes the following aspects:1.Introduce the optical properties of Nd:YAG crystal and Cr4+:YAG crystal,and derive the Q-switching rate equation of Cr4+:YAG crystal.A Q-switched laser was built according to the theory,and a stable Q-switched output with a pulse width of 1.3 ns,a single pulse energy of 360?J,and a peak power of 269.3 kW was obtained,paving the way for the non-linear testing of subsequent experiments.2.Introduce the common preparation methods and principles of two-dimensional material broadband saturable absorber,analyze the advantages and disadvantages of various preparation methods,and use chemical vapor deposition to prepare MoS2 saturable absorber films,and use magnetron sputtering to prepare Mo2C saturable absorber films.3.First,test the saturable absorption characteristics of the prepared MoS2 film and Mo2C film,and obtain the modulation depth,saturated light intensity and other data through formula fitting.Then the thin film is used as a saturable absorber in a solid-state laser.The MoS2 saturable absorber achieves a Q-switched output with a pulse width of 456 ns,a single pulse energy of 91.4 nJ,and a peak power of 200 mW when the pump power is 5.3 W;when the pump power is 3.3 W,the Mo2C saturable absorber,The obtained Q-switched output pulse width is 470 ns,the single pulse energy is 1.61?J,and the peak power is 3.43 W.4.The summary of the full text and the outlook for the future... |
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