摘要
研究了可常规半导体泵浦的Tm∶YLF激光腔内泵浦Ho∶YVO_(4)激光器。利用c-切Tm∶YLF晶体在1909 nm附近的腔内输出波长以更好地匹配Ho∶YVO_(4)晶体的共振吸收带,实现了最高3.3 W的激光输出,中心波长为2052.7 nm,对应的斜率效率和光光转换效率分别为14.5%和11%。得益于Tm∶YLF晶体固有的弱热透镜效应,该腔内泵浦钬激光器在最高激光功率下仍保持高的光束质量,水平方向和垂直方向的光束质量分别为1.33和1.46。所设计的掺钬钒酸盐激光器经济实用,结构紧凑,且易于实现。
Objective The 2.1μm holmium(Ho)laser has important applications in biomedicine,infrared optoelectronic a ntagonism,polymer material processing,and mid-far infrared nonlinear frequency conversion.Compared with mainstream in-band pumped Ho lasers,the intracavity pumped Ho laser can achieve efficient room-temperature Ho laser output based on the compact pump structure of conventional 800 nm laser diode(LD)without additional high-performance 1.9μm thulium-doped(Tm)all-solid-state or fiber laser pump sources.In this Ho laser structure,thulium-doped and Hodoped gain media are placed together in the resonant cavity,and 1.9μm laser is generated in the resonant cavity under the pumping of Tm medium by conventional LD,and the Ho-doped medium is pumped in the same band.Compared with Tm and Ho co-doped lasers with conversion loss,this mechanism has a higher LD-Ho conversion efficiency at room temperature because there is no Tm laser leakage from the cavity during laser operation.In this study,by using Tm∶YLF crystal with negative thermal lens effect to alleviate the combined thermal lens effect of the Ho∶YVO_(4)laser pumped in the cavity,the highest Ho laser output power of 2052 nm is 3.3 W,the slant efficiency is 14.5%,and the LD-Ho laser photoconversion efficienc y is 11%.The acavity-pumped Ho vanadate laser has the highest laser power and laser e fficiency.Methods Polarization absorption spectra of Tm∶YLF crystal sample with Tm atomic fraction of 3%and Ho∶YVO_(4)crystal s ample with Ho atomic fraction of 0.6%are measured using a ultraviolet-vision-near-infrared spectrophotometer.It is u sed to evaluate the spectral overlap between the absorption bands of the Tm∶YLF laser and the Ho∶YVO_(4)crystal in the cavity(Fig.1).The designed intracavity pumped Ho∶YVO_(4)laser adopts a c-cut Tm∶YLF crystal with a size of 3 mm×3 mm×14 mm and an a-cut Ho∶YVO_(4)crystal with a size of 3 mm×3 mm×4 mm(Fig.2).The 2μm laser power is m easured using a pyroelectric power meter.The laser wavelength is measured using a mid-infrared spectrometer.The beam quality of the Ho laser pumped into the cavity is measured using a beam quality(M~2)analyzer.Results and Discussions A Tm∶YLF laser output of 11.38 W is obtained at 92 nm LD incident power of 30 W with a s lope efficiency of 44.3%and light-to-light conversion efficiency of 37.9%.The laser center wavelength measured at the h ighest Tm laser power is 1909.7 nm,corresponding to the fluorescence emission band(σpolarization)along the a-axis of Tm∶YLF crystal(Fig.3).At a pump power of 8.5 W under the wavelength of 792 nm,the laser oscillates and achieves the highest Ho∶YVO_(4)laser output of 3.3 W,and the corresponding LD-Ho laser optical conversion efficiency reaches 11%[Fig.4(a)].The fitting results show that the slope efficiency of the Ho laser reaches 14.5%,which is s ignificantly higher than that of the Tm∶YAP-pumping Ho∶YVO_(4)laser(10.4%).The leaky 1909 nm Tm∶YLF laser is d etected near the threshold pumping power(8.5--9.8 W),and then the Tm laser signal disappears and Ho∶YVO_(4)laser starts to vibrate[Fig.4(b)].In the process of increasing the output power,the output wavelength of the Ho laser is stable at(2052.2±0.5)nm,and no residual Tm laser signal is detected.This phenomenon can be interpreted as follows:w hen the Ho laser starts to vibrate near the threshold value,the energy consumed by the Tm laser in the cavity is limited,and the Tm laser signal can be observed.With an increase in Ho laser power,the energy consumed by the Tm laser increases.At this point,the Tm laser enters a new steady state,and the gain generated by LD pumping is mainly balanced with the resonant absorption loss of the Ho∶YVO_(4)crystal.Compared to the strong Ho laser signal,the Tm laser leakage signal is so weak that it is drowned in spectral noise.The beam quality in the horizontal and vertical directions at the highest Ho laser power is 1.33 and 1.46,respectively(Fig.5).Conclusions Tm∶YLF laser intracavity pumped Ho∶YVO_(4)laser with a compact structure and direct pumping by a c onventional laser diode is reported.To achieve efficient overlap of the absorption band between the Tm∶YLF laser and Ho∶YVO_(4)crystal,a Tm∶YLF crystal cut along the c-axis is used to achieve theσ-polarized Tm laser output near 1909 nm,which is verified by the Ho laser pumped into the cavity.In the Tm∶YLF laser experiment,a maximum output of 11.3 W with 1910 nm Tm laser is achieved,with a corresponding slope efficiency of 44.3%and light-to-light conversion e fficiency of 37.9%.The highest 2052 nm laser output power of 3.3 W is achieved with the intracavity pumped Ho∶YVO_(4)l aser.Owing to the weak thermal lens effect of the Tm∶YLF crystal,intracavity pumped Ho∶YVO_(4)laser output is guaranteed with high beam quality.The above-mentioned results indicate that the room-temperature Ho laser can be pumped at the watt level from the Ho vanadate-doped crystal by the direct pumping of a conventional LD.
作者
吴鸿春
Wu Hongchun(Key Laboratory of Research on Chemistry and Physics of Optoelectronic Materials,Fujian Institute of Research on the Structure of Matter,Chinese Academy of Science,Fuzhou 350002,Fujian,China;University of Chinese Academy of Sciences,Beijing 100049,China)
出处
《中国激光》
EI
CAS
CSCD
北大核心
2022年第23期53-57,共5页
Chinese Journal of Lasers
基金
国家自然科学基金(61875200)。
关键词
激光器
掺钬钒酸钇
掺铥氟化钇锂
腔内泵浦
2.1μm
lasers
holmium-doped yttrium vanadate
thulium-doped yttrium fluoride lithium
intracavity pumping
2.1μm
