The multiphoton ultraviolet and visible upconversion luminescence of Tm3+Yb3+ codoped ZBLAN fluoride glass as
excited by a 975nm diode laser was studied. Two typical ultraviolet 290.6nm 1I6 → 3H6 and 362.0nm 1D2 → 3H6 upconversion luminescence lines were found. The careful measurement of the variation of upconversion luminescence intensity F as a function of the 975nm pumping laser power P has proven that the 290.6nm 1I6 → 3H6 and 362.0nm 1D2 → 3H6 upconversion luminescences are a six-photon and a five-photon upconversion luminescence respectively. Several visible upconversion luminescence lines at 450.5nm, 473.9nm, 648.5nm, (687.3nm, 696.2nm) and (793.5nm, 800.7nm)
were found also, which result from the fluorescence transitions of 1D2 → 3F4, 1G4 → 3H6, 1G4 → 3F4, 3F3 → 3H6 and 3H4 → 3H6 of Tm3+ ion respectively. It has been proved that the upconversion luminescence of 1G4 state is a three-photon upconversion process, while that of 3F3 or 3H4 state is a two-photon upconversion process. The theoretical analysis
suggests that the upconversion mechanism of the 362.0nm 1D2 → Tm3+ upconversion luminescence is the cross energy
transfer of {3H4(Tm3+) → 3F4(Tm3+), 1G4(Tm3+) → 1D2(Tm3+)} and {1G4(Tm3+) → 3F4(Tm3+), 3H4(Tm3+) → 1D2(Tm3+)} between Tm3+ ions, whereas the mechanism of the 290.6nm 1I6 → 3H6 upconversion luminescence is the sequential energy transfer of {2F5/2(Yb3+) → 2F7/2(Yb3+), 1D2(Tm3+) → 3P1(Tm3+)} and {2F5/2(Yb3+) → 2F7/2(Yb3+), 1D2(Tm3+) → 3P2(Tm3+)} from Yb3+ ions to Tm3+ ions. In addition, the upconversion luminescence of G4 and 3H4 state
also results from the sequential energy transfer {2F5/2(Yb3+) → 2F7/2(Yb3+), 3H4(Tm3+) → 1G4(Tm3+)} and {2F5/2(Yb3+) → 2F7/2(Yb3+), 3F4(Tm3+) → 3F2(Tm3+)} from Yb3+ ions to Tm3+ ions respectively.
This paper analyzes the reflection index modulation distribution and the corresponding spectrum characteristic of the holographic reflection gratings fabricated by Lippman light path under the condition of recording medium absorption being taken into account. The emphasis of discussion is placed on the relationship of secondary peak characteristic of the holographic reflection gratings, bandwidth and the distribution of refraction index modulation under this recording condition, calculating and simulating the distribution curve of refraction index modulation and the corresponding spectrum characteristic curve of diffraction gratings, and the comparison with the holograph gratings recorded by symmetrical light path. The result of calculation shows that there is obvious difference between the spectrum characteristic curve of Lippman holographic gating and that of symmetrical light path, and the secondary peak value of Lippman holographic gratings is lower than that of symmetric light path under the condition of the same reflection index modulation, while the medium of recording is thicker (thicker than 60μm) or the non-linear modulation of refraction index is relatively large, and the higher secondary peak of Lippman holographic gratings presents saw-like and non-degressive, whereas this phenomenon has never occurred in the holographic gratings diffraction recorded by the symmetrical path. This result obtained by calculation and simulation is consistent with experimental result.
The diffraction characteristics of the volume holographic gratings made by multi-exposures with angular multiplexing during its construction is investigated. Because of the reflection by the interface between the emulsion and the substrate or the air there is an extra unslanted periodic structure inside a slanted grating, it will affect properties of the slanted volume holographic gratings. When the angle between the surface of the substrate and the grating plane of the slanted grating is less than a certain value, an extra peak accompanying the main peak will appear in the diffraction spectrum. But, when the angle is larger than the certain value, one designed and expected main peak will disappeared while the extra peak is kept and observed. This phenomenon limits the capacity of the volume hologram for the application in wavelength-division multiplexing (WDM).
The measurements on the intensity of the diffracted beam of transmission gratings were done. The gratings with different center-to-center separation were illuminated by the light beams with different polarizations, the ratio between the intensities of P-polarization and S-polarization shows clearly the vector properties of grating.
The nonlinear refractive index model is used to analyze the diffraction properties of reflection volume hologram. Using characteristic matrix method of multi-layer system, we analyzed the wavelength selectivity and angular selectivity of the diffraction efficiency of reflection volume hologram for P and S polarization. Compared to the classic pure sinusoidal index modulation, this nonlinear model gave more practical results.
The crosstalk performance of a four-port electrooptic tunable filter in lithium niobate is analyzed, based on the transient response of the filter to an input optical pulse. Crosstalk is calculated for Blackman apodizing functions for input pulse widths representative of high-data-rate systems. It is concluded that crosstalk level below -30 dB for 20 Gb/s data rates and 100 GHz channel spacing is achievable with presently available substrate dimensions.
The laboratory experimental test of sound speed for fresh water and typical salt water (salinity Sequals35%) are reported for different water temperatures. Considering that the returned signal contains both Rayleigh and Brillouin peak (which have Gaussian and Lorentzian line shapes respectively), the measured data are fitted by mixed function of Gaussian and Lorentzian. Then, the sound speed is obtained by Brillouin shift that is determined with FSR of the Fabry-Perot. For the testing of submerged object, it has fewer requirements on the accuracy. The experimental results without and with submerged object are given. All results show that Brillouin scattering is a good method for measuring sound speed in water and for testing of submerged object.
A new application of holography and interferometry in temperature sensing is proposed in this paper. Using holographic technique and electron lithography, a grating can be made in a fiber's end. This structure can be used to test the temperature change. By examining the interfering pattern of diffract lights of the grating, the temperature change can be calculated. If using the work wavelength of 1.55micrometers , the temperature testing range can theoretically be 1179 degree(s)C.
A new physical model for volume hologram was proposed. Volume hologram was considered as a series coupled Fabry- Perot etalon. The multi beam interference makes band width of volume hologram to be very narrow. The positive feedback of Fabry-Perot provide high diffraction efficiency of volume hologram. Computer simulations based on the new model showed a good consistency with the coupled wave theory and previous experimental results.
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