| Mid-infrared lasers have broad application prospects in military,medical,atmospheric remote sensing,molecular spectroscopy,environmental detection,space communication and other fields.In particular,the 3μm region laser is located at the strong absorption peak of water,and has important application value in ophthalmology,dentistry and minimally invasive surgery.In addition,the 3μm band laser is also an efficient pump source for the generation of long-wave midinfrared lasers.The laser diode(LD)direct pump procedure is an important technical approach to generate 3μm band laser.Such technology might have broad commercial prospects and is currently the research focus in the field of high-power mid-infrared laser.LD directly pumped Erbium ion(Er3+)doped crystal can produce mid-infrared 2.8μm laser,which has the advantages of compact structure,small size and better stability.CaF2 and SrF2 crystals are easy to grow in large size,with high transmittance and low phonon energy,and are considered to be one of the most commercially promising optical materials.Especially in recent years,with the development of crystal growth technology,Er3+:CaF2/SrF2 crystal has attracted wide attention in the direct generation of 3μm region mid-infrared laser.The unique fluorite structure of CaF2/SrF2 crystals can easily enrich Er3+to form "clusters",which can enhance the energy transfer process between Er3+and inhibit the 2.8μm laser self-termination effect.In particular,CaF2/SrF2 crystals doped with low concentration of Er3+have outstanding advantages in 2.8μm mid-infrared laser generation,and relevant laser characteristics need to be explored,which has broad commercial prospects.In this thesis,theoretical and experimental studies are carried out on the characteristics of the all-solid-state 2.8μm Er:CaF2/SrF2 laser pumped by LD.The laser technology is closely combined with crystal physics,and the laser performance parameters of the crystal are comprehensively characterized.The output characteristics of the 2.8μm high-power continuous-wave laser,pulsed laser,ultra-short pulse laser and single-frequency laser are mainly studied.It provides an important reference for the further optimization of crystal growth.Follows are summarized main research contents and innovations:1.The principle,application and research status of 3μm region solid-state laser by LD directly pumped were studied.The luminescence mechanism of Er:CaF2 crystal and the principle of 2.8μm laser generation are studied theoretically.The research status of all-solid-state pulsed laser,ultra-short pulsed laser and single frequency laser is reviewed.The design idea of laser resonator is analyzed.The development status of a novel 2D material saturable absorption modulator for pulsed laser is investigated2.High efficiency 2.8μm laser generated directly by LD-pumped lightly-doped Er:CaF2 crystals.Based on the excellent optical properties,a lightly-doped 1.7at.%Er:CaF2 crystal is directly pumped by a LD with a central wavelength of 980 nm,and 2.32 W mid-infrared 2.8 μm high power continuous-wave laser operation is successfully obtained.This is currently the highest output power of LD pumped Er3+fluoride doped crystal laser.A 2.8μm laser with a maximum output power of 350 mW was obtained by upconversion cooperative pumping.It is proved that 2.8μm laser output can also be achieved in llghtly-doped Er:CaF2 crystal due to the presence of energy upconversion process.The experimental results show that Er:CaF2 crystal doped with lightly concentration is an excellent mid-infrared laser material and has broad market prospects.3.Study on the characteristics of LD pumped 2.8μm region Er:CaF2 Q-switched pulsed laser.The actively and passively Q-switched laser properties of Er:CaF2 crystals were investigated theoretically and experimentally.In the passive Q-switching operation,by comparing the pulse laser performance of a variety of 2D material saturable absorption modulator,it is found that the Q-switched laser has the best performance with Graphdiyne(GDY)modulator.The 2.8μm passively Q-switched mode-locked laser was successfully realized by applying GDY to the generation of ultra-short pulse laser.The results demonstrate the potential of the GDY saturable absorption modulator in mid-infrared ultra-short pulse laser generation.It makes up for the lack of commercial modulator in 3μm band and brings a new direction to the development of ultra-short pulse.4.Characteristics of LD pumped Er:CaF2-SrF2 mixed crystal 2.73μm continuous-wave mode-locked laser.Using SESAM modulator,an all-solid-state 2.73μm continuous-wave modelocked laser was successfully achieved.The maximum output power of the laser is 93 mW,the repetition rate is 69 MHz,and the signal-to-noise ratio is 71 dB.To the best of our knowledge,this is the first demonstration in the mid-infrared region of the Er:CaF2-SrF2 all-solid-state continuouswave mode-locking laser with SESAM modulator.5.Study on the characteristics of 2.8 μm solid-state single-frequency laser generated directly by LD pumping.The single-frequency laser characteristics of LD-pumped Er:CaF2 crystals in different cavity types were studied by using intracavity F-P standard technique.The results show that a bidirectional single-frequency laser with excellent performance can be obtained by combining the ring cavity with the F-P etalons.A 2.8 μm solid-state single-frequency laser with stable frequency and switchable wavelength has been successfully realized by using the F-P etalon technology in a ring cavity.The central wavelength of the single-longitudinal mode lasers is 2728 nm and 2794 nm,and the maximum output powers are 268 mW and 440 mW,respectively.The corresponding single longitudinal mode linewidths are 25 MHz and 11 MHz,respectively.The experimental results show that the central wavelength of the single longitudinal mode laser is almost constant with the increase of the incident pump power.This is the first single-longitudinal mode laser in the 3 μm band using LD directly pumped bulk crystals. |
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