Long-wavelength Mid-infrared Fiber Laser Based On Novel Structure

The mid-infrared lasers around³?m band have wild applications in the fields of national defense,medicine and environmental protection,which has aroused people's strong attention.Compared to the continuous and mode-locked fiber lasers,Q-switched fiber lasers around 3?m can provide enenrgy of ns or ms pulse duration,which is ideal for special applications such as gas sensing,plastic and polymer proceeding,laser scalels,non-invasive medical diagnostics,infrared countermeasures and lidar.This paper mainly studied the passive Q switched pulse based on Ho³⁺/Pr³⁺co-doped and Dy³⁺-doped fluoride?ZBLAN?fiber laser.The specific research contents are as follows:1.We performed a detailed analysis of the transition of³?m laser generated in Ho³⁺/Pr³⁺co-doped ZBLAN fiber,and established a passive Q-switched rate equation based on Ho³⁺/Pr³⁺co-doped ZBLAN fiber.After numerical simulation analysis,we optimized the fiber length and dopant concertration to achieve a high slope efficiency,low laser threshold laser,and also analyzed the pulse output characteristics?repetition,pulse width?as a function of pump power.When the fiber length,Ho³⁺and Pr³⁺-ion doping concentrations was 5 m,3 mol.%and 0.25 mol.%,respectively,a fiber laser of high slope efficiency?32.6%?and low laser threshold?162.6 mW?was achieved.The analysis provided theoretical guidance for the subsequent passive Q-switched Ho³⁺/Pr³⁺co-doped ZBLAN fiber laser.2.Based on the numerical simulation,we built a passive Q-switched Ho³⁺/Pr³⁺co-doped ZBLAN fiber laser by using GNR material.In experiment we adopted a ZBLAN fiber with the length of 5.2 m,and Ho³⁺-ion and Pr³⁺-ion dopant concentration was 3 mol.%and 0.25 mol.%respectively,then we utilized 1150 nm laser diode?LD?as the pump source and GNR saturable absorber?SA?as the pulse modulation device.When the pump source power was up to 244.7 mW,a Q-switched pulse with a maximum output power of20 mW was obtained.The operating wavelength was 2.868?m,and the maximum repetition rate and minimum pulse width are 55.5 kHz and 2.12?s,respectively.3.In order to modulate the³?m pulse better,a large aspect ratio gold nanorod?LAR-GNR?with an aspect ratio of²0 was obtained by changing the GNR seed growth process.Then base on the LAR-GNR,we built a tunable Ho³⁺/Pr³⁺co-doping ZBLAN fiber laser.Among them,the wavelength tuning device was a planar blazed grating.We analyzed the characteristics of the output pulse?e.g.repetition frequency,pulse width?as a function of pump source power and wavelength.When the pump power was up to 307.2mW,the wavelength tuning range is 2834.5²881.0 nm,and the maximum output power was 30.8 mW,its maximum repetition frequency and minimum pulse width were 78.12kHz and 2.18?s,respectively.4.Firstly,the possibility of long wavelength and broadband tunability of doped Dy³⁺ions was analyzed from the emission cross section of doped ions.In the experiment,1100nm LD was used as the pump source,the grating was adoped as the wavelength tuning device,and the wide-band semiconductor saturable absorption mirror?SESAM?was utilized as the pulse modulation device.Then we adopted a ZBLAN fiber with a length of 1.2 m and Dy³⁺-ion dopant concentration of 0.1 mol.%.Finally,we obtained a passive Q-swithed pulse with the maximum output power of 171.3 mW.The wavelenth tuning range of the pulse was from 2854 nm to 2995.6 nm?141.6 nm?,which is the widest range of³?m tunable passive Q-switched pulses to date.