We discover that the spatially coherent radiation within a certain frequency range can be obtained without a common nonlinear optical process.Conventionally,the emission spectra were obtained by de-exciting excited centers from real excited energy levels to the ground state.Our findings are achieved by deploying a high-entropy glass system(HEGS)doped with neodymium ions.The HEGS exhibits a much broader infrared absorption than common glass systems,which can be attributed to be high-frequency optical branch phonons or allowable multi-phonon processes caused by phonon broadening in the system.A broadened phonon-assisted wideband radiation(BPAWR)is induced if the pump laser is absorbed by the system.The subsequent low-threshold self-absorption coherence modulation(SACM)can be controlled by changing excitation wavelengths,sample size,and doping concentrations.The SACM can be red-shifted through the emission of phonons of the excited species and be blue-shifted by absorbing phonons before they are de-excited.There is a time delay up to 1.66 ns between the pump pulse and the BPAWR when measured after traveling through a 35 mm long sample,which is much longer than the Raman process.The BPAWR-SACM can amplify the centered non-absorption band with a gain up to 26.02 dB.These results reveal that the shift of the novel radiation is determined by the frequency of the non-absorption band near the absorption region,and therefore the emission shifts can be modulated by changing the absorption spectrum.When used in fiber lasers,the BPAWR-SACM process may help to achieve tunability.

Linde Zhang;Jingyuan Zhang;Xiang Wang;Meng Tao;Gangtao Dai;Jing Wu;Zhangwang Miao;Shifei Han;Haijuan Yu;Xuechun Lin

Laboratory of All-solid-state Light Sources,Beijing Engineering Research Center,Institute of Semiconductors,Chinese Academy of Sciences,100083 Beijing,China;Synlumin Conuninex(Shanghai)Enterprise Development Co.,Ltd.,201401 Shanghai,China;Time-wave-space Optical Technology(Xiaogan)Co.,Ltd.,432012 Xiaogan,Hubei,China;High-dimensional Plasma Sources Technology(Xiaogan)Co.,Ltd.,432012 Xiaogan,Hubei,China

光：科学与应用（英文版）

[1]Linde Zhang;Jingyuan Zhang;Xiang Wang;Meng Tao;Gangtao Dai;Jing Wu;Zhangwang Miao;Shifei Han;Haijuan Yu;Xuechun Lin-.Design of coherent wideband radiation process in a Nd3+-doped high entropy glass system)[J].光：科学与应用（英文版）,2022(11):2065-2076

HEGS,BPAWR

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