As a crucial parameter in the design and analysis of laser performances, stimulated emission(SE) cross-section is currently considered to be dependent on several factors, such as temperatures and eigen-polarizations f...As a crucial parameter in the design and analysis of laser performances, stimulated emission(SE) cross-section is currently considered to be dependent on several factors, such as temperatures and eigen-polarizations for anisotropic crystals. In contrast with these factors, impact of propagating directions upon SE cross-section has garnered less attention.In this paper, to investigate the SE cross-section in arbitrary propagating directions, fluorescence spectra for the transition ~4F_(3/2)→~4I_(11/2) in Nd:YVO_4 are measured in different propagating directions. Based on Fuchtbauer–Ladenburg equation model, the propagating direction-dependent SE cross-section spectra in Nd:YVO_4 are obtained for the first time, to our best knowledge. A novel concept of anisotropic SE cross-section is proposed to interpret the propagating direction-dependent effect. The experiment results reveal that for an arbitrary propagating direction the SE cross-section of e light around 1064 nm can be expressed as a superposition from two principle axial propagating directions with a weight of plane projection.展开更多
The vacuum electromagnetic field has been a mystery ever since Hedrik Casimir [1] 08D0C9EA79F9BACE118C8200AA004BA90B02000000080000000E0000005F005200650066003400310035003500370032003300390030000000 proposed in 1948 tha...The vacuum electromagnetic field has been a mystery ever since Hedrik Casimir [1] 08D0C9EA79F9BACE118C8200AA004BA90B02000000080000000E0000005F005200650066003400310035003500370032003300390030000000 proposed in 1948 that it actually existed and could be measured. Many subsequent experiments [2] 08D0C9EA79F9BACE118C8200AA004BA90B02000000080000000E0000005F005200650066003400310035003500370032003300390033000000 have confirmed that its vast field strength (over a terawatt/cm2) is real and matches quantum predictions. Radiation pressures as high as 18 psi have been measured from the reflected vacuum light between plates of 10 nanometer separation. All of this creates a mystery. The electromagnetic field strength is more than a terawatt/cm2 everywhere in the universe and yet nothing is melted, ionized or burned up by the field. This paper extracts new insight from Einstein’s famous 1917 paper, credited with the discovery of stimulated emission and still believed today. The result is a practical explanation of the vacuum field and its observed properties.展开更多
In 1917, Einstein published his paper [1] renowned for the discovery of stimulated emission. However, it also contained the principles which allowed the calculation of the universal photonic cross-section = λ2/2π. A...In 1917, Einstein published his paper [1] renowned for the discovery of stimulated emission. However, it also contained the principles which allowed the calculation of the universal photonic cross-section = λ2/2π. Any heavy electronic system will have this cross-section for photonic excitation and stimulated emission in its rest frame. The modifications of this cross-section due to the recoil of the emitter have not yet been calculated, but are in general expected to be second order in recoil velocity.展开更多
Karst fracture-cavity carbonate reservoirs,in which natural cavities are connected by natural fractures to form cavity clusters in many circumstances,have become significant fields of oil and gas exploration and explo...Karst fracture-cavity carbonate reservoirs,in which natural cavities are connected by natural fractures to form cavity clusters in many circumstances,have become significant fields of oil and gas exploration and exploitation.Proppant fracturing is considered as the best method for exploiting carbonate reservoirs;however,previous studies primarily focused on the effects of individual types of geological formations,such as natural fractures or cavities,on fracture propagation.In this study,true-triaxial physical simulation experiments were systematically performed under four types of stress difference conditions after the accurate prefabrication of four types of different fracture-cavity distributions in artificial samples.Subsequently,the interaction mechanism between the hydraulic fractures and fracture-cavity structures was systematically analyzed in combination with the stress distribution,cross-sectional morphology of the main propagation path,and three-dimensional visualization of the overall fracture network.It was found that the propagation of hydraulic fractures near the cavity was inhibited by the stress concentration surrounding the cavity.In contrast,a natural fracture with a smaller approach angle(0°and 30°)around the cavity can alleviate the stress concentration and significantly facilitate the connection with the cavity.In addition,the hydraulic fracture crossed the natural fracture at the 45°approach angle and bypassed the cavity under higher stress difference conditions.A new stimulation effectiveness evaluation index was established based on the stimulated reservoir area(SRA),tortuosity of the hydraulic fractures(T),and connectivity index(CI)of the cavities.These findings provide new insights into the fracturing design of carbonate reservoirs.展开更多
Sm^(3+) ions incorporated Sm_(2)Si_(2)O_(7) crystalline phase formed in the aluminoborosilicate glass matrix synthesized via melting quenching technique followed by heat-treatment process is reported herewith.The prel...Sm^(3+) ions incorporated Sm_(2)Si_(2)O_(7) crystalline phase formed in the aluminoborosilicate glass matrix synthesized via melting quenching technique followed by heat-treatment process is reported herewith.The preliminary confirmation on the obtained glass ceramics was made through X-ray diffration(XRD) studies.Formation of non-bridging oxygens(NBOs) in the glass network and the modes of vibrations of network units we re analyzed through Fourier transform infrared spectroscopy(FTIR) studies.Surface morphology of heat-treated samples at varying temperatures was determined via a field emission scanning electron microscope(FESEM).The absorption studies on heat-treated samples signify the low bandgap values and high Urbach energy values due to improved crystallinity in the glass network.Judd-Ofelt intensity parameters identified for visible absorption transitions follow the trend of Ω_(4)>Ω_(2)>Ω_(6).Excitation and emission studies on heat-treated samples show improvement in their intensities compared to the unheated base glass.The thermal quenching is observed at higher temperatures(540 and 580℃ for 3 h) of heat-treated samples.Calculations based on luminescence spectra including radiative transition probability,stimulated emission cross-section and branching ratio show good results for glass ceramics prior to precursor glass.Longer lifetimes of Sm^(3+) ions(milliseconds) in the level ^(4)G_(5/2) are seen for glass ceramics.Color coordinates suggest the reddish-orange emissions from prepared glass ceramics.Thus,Sm^(3+) doped Sm_(2)Si_(2)O_(7) glass ceramics are favorable materials for solid-state lighting and laser applications.展开更多
文摘As a crucial parameter in the design and analysis of laser performances, stimulated emission(SE) cross-section is currently considered to be dependent on several factors, such as temperatures and eigen-polarizations for anisotropic crystals. In contrast with these factors, impact of propagating directions upon SE cross-section has garnered less attention.In this paper, to investigate the SE cross-section in arbitrary propagating directions, fluorescence spectra for the transition ~4F_(3/2)→~4I_(11/2) in Nd:YVO_4 are measured in different propagating directions. Based on Fuchtbauer–Ladenburg equation model, the propagating direction-dependent SE cross-section spectra in Nd:YVO_4 are obtained for the first time, to our best knowledge. A novel concept of anisotropic SE cross-section is proposed to interpret the propagating direction-dependent effect. The experiment results reveal that for an arbitrary propagating direction the SE cross-section of e light around 1064 nm can be expressed as a superposition from two principle axial propagating directions with a weight of plane projection.
文摘The vacuum electromagnetic field has been a mystery ever since Hedrik Casimir [1] 08D0C9EA79F9BACE118C8200AA004BA90B02000000080000000E0000005F005200650066003400310035003500370032003300390030000000 proposed in 1948 that it actually existed and could be measured. Many subsequent experiments [2] 08D0C9EA79F9BACE118C8200AA004BA90B02000000080000000E0000005F005200650066003400310035003500370032003300390033000000 have confirmed that its vast field strength (over a terawatt/cm2) is real and matches quantum predictions. Radiation pressures as high as 18 psi have been measured from the reflected vacuum light between plates of 10 nanometer separation. All of this creates a mystery. The electromagnetic field strength is more than a terawatt/cm2 everywhere in the universe and yet nothing is melted, ionized or burned up by the field. This paper extracts new insight from Einstein’s famous 1917 paper, credited with the discovery of stimulated emission and still believed today. The result is a practical explanation of the vacuum field and its observed properties.
文摘In 1917, Einstein published his paper [1] renowned for the discovery of stimulated emission. However, it also contained the principles which allowed the calculation of the universal photonic cross-section = λ2/2π. Any heavy electronic system will have this cross-section for photonic excitation and stimulated emission in its rest frame. The modifications of this cross-section due to the recoil of the emitter have not yet been calculated, but are in general expected to be second order in recoil velocity.
基金sponsored by the National Natural Science Foundation of China(Grants Nos.52104046 and 52104010).
文摘Karst fracture-cavity carbonate reservoirs,in which natural cavities are connected by natural fractures to form cavity clusters in many circumstances,have become significant fields of oil and gas exploration and exploitation.Proppant fracturing is considered as the best method for exploiting carbonate reservoirs;however,previous studies primarily focused on the effects of individual types of geological formations,such as natural fractures or cavities,on fracture propagation.In this study,true-triaxial physical simulation experiments were systematically performed under four types of stress difference conditions after the accurate prefabrication of four types of different fracture-cavity distributions in artificial samples.Subsequently,the interaction mechanism between the hydraulic fractures and fracture-cavity structures was systematically analyzed in combination with the stress distribution,cross-sectional morphology of the main propagation path,and three-dimensional visualization of the overall fracture network.It was found that the propagation of hydraulic fractures near the cavity was inhibited by the stress concentration surrounding the cavity.In contrast,a natural fracture with a smaller approach angle(0°and 30°)around the cavity can alleviate the stress concentration and significantly facilitate the connection with the cavity.In addition,the hydraulic fracture crossed the natural fracture at the 45°approach angle and bypassed the cavity under higher stress difference conditions.A new stimulation effectiveness evaluation index was established based on the stimulated reservoir area(SRA),tortuosity of the hydraulic fractures(T),and connectivity index(CI)of the cavities.These findings provide new insights into the fracturing design of carbonate reservoirs.
基金supported by Department of Science and Technology (DST)-Science and Engineering Research Board (SERB),Government of India(DST-SERB-EMR/2017/001548)。
文摘Sm^(3+) ions incorporated Sm_(2)Si_(2)O_(7) crystalline phase formed in the aluminoborosilicate glass matrix synthesized via melting quenching technique followed by heat-treatment process is reported herewith.The preliminary confirmation on the obtained glass ceramics was made through X-ray diffration(XRD) studies.Formation of non-bridging oxygens(NBOs) in the glass network and the modes of vibrations of network units we re analyzed through Fourier transform infrared spectroscopy(FTIR) studies.Surface morphology of heat-treated samples at varying temperatures was determined via a field emission scanning electron microscope(FESEM).The absorption studies on heat-treated samples signify the low bandgap values and high Urbach energy values due to improved crystallinity in the glass network.Judd-Ofelt intensity parameters identified for visible absorption transitions follow the trend of Ω_(4)>Ω_(2)>Ω_(6).Excitation and emission studies on heat-treated samples show improvement in their intensities compared to the unheated base glass.The thermal quenching is observed at higher temperatures(540 and 580℃ for 3 h) of heat-treated samples.Calculations based on luminescence spectra including radiative transition probability,stimulated emission cross-section and branching ratio show good results for glass ceramics prior to precursor glass.Longer lifetimes of Sm^(3+) ions(milliseconds) in the level ^(4)G_(5/2) are seen for glass ceramics.Color coordinates suggest the reddish-orange emissions from prepared glass ceramics.Thus,Sm^(3+) doped Sm_(2)Si_(2)O_(7) glass ceramics are favorable materials for solid-state lighting and laser applications.
