Study On The Pulse Laser Characteristics Of LD-pumped Rare-earth-doped CaF₂ Crystal

LD-pumped solid-state lasers are widely used due to the advantages of economic applicability, long life, stable operation, high efficiency and so on. In order to obtain a stable solid-state laser, the luminescent particles that are able to realize the population inversion are essential. The luminescent particles are called active population. The rare-earth ions are a huge luminous treasury, because they have abundant energy levels and 4f electronic transition properties. To neodymium ions?Nd3+? and ytterbium ions?Yb3+?, as 1 ?m active ions, the laser characteristics are sustaining to obtain the new breakthrough. Erbium ions?Er3+?, as 2.8 ?m mid-infrared active ions, have maintained vitality.Along with the development of technology, the performance of a simple laser beam often can not meet the needs of the application, so we need to continue to develop and improve the quality of the laser output characteristics. The Q-switching and the mode-locking techniques are developed in order to obtain a narrow pulse width and high peak power of the laser beam. For that, saturable absorber is an important component.In this article, the new style Nd,La:CaF₂ crystals and Yb,Y:CaF₂ crystals were used to further study the laser characteristics in 1 ?m band. While Er:CaF₂ crystals were used for the study of mid-infrared laser characteristics. Using the graphene absorber and the new types black phosphorus absorber, the pulse lasers were researched.1. The Q-switched principle and the mode-locked principle to generate the pulsed laser were illustrated. For 1 ?m and 2.8 ?m band, the development of laser crystal materials had been recommended. The two-dimensional saturable absorbers were also explained.2. The laser characterizations of the new style Nd,La:CaF₂ crystals were firstly detailedly researched. Using the appropriate LD pumping, the continuous wave and the Q-switched laser characteristics were studied in detail. The Q-switched lasers were researched, including the output power characteristics, the pulse width, the repetition rate, the wavelength and so on. Using a semiconductor saturable absorber mirror?SESAM? as saturable absorber, the mode-locked laser generated pulses with pulse duration of 11 ps and repetition rate of 87.5 MHz at the central wavelength of 1065.8 nm?a full width at half maximum of 2.1 nm?. The maximum average output power was 110 mW?slope efficiency of 7.8%? corresponding to pulse energy of 1.26 nJ and peak power of 115 W, respectively.3. A tri-wavelength synchronous mode-locking operation of a diode-pumped Yb,Y:CaF₂ laser had been investigated at 1 ?m. The tri-wavelength synchronous mode-locking pulses were centered at 1045.7 nm, 1047.6 nm and 1049.5 nm. An interference pattern was obtained in the autocorrelation trace. The envelope pulse width was 120 ps assuming the Gauss fit. The period of beat pulses was 6.8 ps, which was corresponding to frequency difference of 0.52 THz among the three wavelengths. The mode-locked laser generated maximum average output power of 196 mW, slope efficiency of 7.2%, repetition rate of 89 MHz.4. End-pumped by a fiber-coupled LD, a mid-infrared Er doped CaF₂ crystal was successfully demonstrated at 2.8 ?m. An efficient 2.8 ?m stable passively Q-switched Er:CaF₂ laser was demonstrated with a graphene saturable absorber. Under an absorbed pump power of 2.353 W, an average output power of 172 mW was generated with a pulse duration of 1.324 ?s and a repetition rate of 62.70 kHz, corresponding to the single pulse energy of 2.74 ?J and the peak power of 2.07 W, respectively. And the Q-switched Er:CaF₂ laser had a high slope efficiency of 10.37%.5. In this paper, the new multi-layer black phosphorus was firstly applied to Er:CaF₂ laser. Multi-layer black phosphorus as saturable absorber, the laser features were reached in-depth, including the output power characteristics, pulse width and repetition rate. When the transmission of 3% for output mirror and the absorbed pump of 2.353 W, the average output power was 178 mW with the high slope efficiency of 11.48%. The pulse duration was 954.8 ns and the repetition rate was 41.93 kHz, corresponding to the pulse energy of 4.25 ?J and a pulse peak power of 4.45 W. When the transmission of output mirror was 1%, stably Q-switched pulses with duration of 940.5 ns under a repetition rate of 50.11 kHz. The pulse energy and the pulse peak power were 2.47 ?J and 2.63 W. The results suggest that the multilayer BP can be an attractive candidate of SA for Q-switched laser near 3 ?m wavelength.