Doped ZBLAN Glass Research Articles

Model of laser cooling in theYb3+-doped fluorozirconate glass ZBLAN

A quantitative description of optical refrigeration in ${\mathrm{Yb}}^{3+}$-doped ZBLAN glass in the presence of transition-metal and $\mathrm{OH}$ impurities is presented. The model includes the competition of radiative processes with energy migration, energy transfer to transition-metal ions, and multiphonon relaxation. Molecular dynamics calculations of pure ZBLAN and ZBLAN doped with transition-metal ions provide the structural information that, when combined with spectroscopic data, allows for the calculation of electric-dipole energy-transfer rates in the framework of the Dexter theory. The structural data is further used to extend the traditional energy-gap law to multiphonon relaxation via vibrational impurities. The cooling efficiency is sensitive to the presence of both $3d$ metal ions with absorption in the near infrared and high-frequency vibrational impurities such as $\mathrm{OH}$. The calculation establishes maximum impurity concentrations for different operating temperatures and finds ${\mathrm{Cu}}^{2+}$, ${\mathrm{Fe}}^{2+}$, ${\mathrm{Co}}^{2+}$, ${\mathrm{Ni}}^{2+}$, and $\mathrm{OH}$ to be the most problematic species. ${\mathrm{Cu}}^{2+}$ in particular has to be reduced to $l2\phantom{\rule{0.3em}{0ex}}\mathrm{ppb}$, and ${\mathrm{Fe}}^{2+}$, ${\mathrm{Co}}^{2+}$, ${\mathrm{Ni}}^{2+}$, and $\mathrm{OH}$ have to be reduced to $10--100\phantom{\rule{0.3em}{0ex}}\mathrm{ppb}$ for a practical $\mathrm{ZBLAN}:{\mathrm{Yb}}^{3+}$ optical cryocooler to operate at $100--150\phantom{\rule{0.3em}{0ex}}\mathrm{K}$.

Ultraviolet upconversion emission from ZBLAN glass doped with Tm 3+ ions

The ultraviolet upconversion emission properties from Tm 3+ ions doped ZBLAN glass upon 463 nm laser excitation have been studied. Two ultraviolet emission bands, centered at 347 nm for 1I 6→ 3F 4 Tm 3+ transition and 362 nm for 1D 2→ 3H 6 Tm 3+ transition, have been observed. The responsible upconversion mechanisms were investigated by measuring time evolution spectra.

Energy transfer and frequency upconversion in Pr3+-doped ZBLAN glass

The lifetimes of 3P0 and 1D2 levels of Pr3+ were measured in ZBLAN glasses of composition in mol% 53ZrF4–20BaF2–(4−x)LaF3–3AlF3–20NaF–xPrF3 (x=0.1, 0.5, 1, and 3) by resonant excitation. Energy transfer observed between Pr3+ ions was analyzed by means of the Inokuti–Hirayama theory. The non-exponential dependence of the 1D2 decay on Pr3+ concentration indicates that dipole–dipole interaction between Pr3+ is the main process. Orange-to-blue upconversion luminescence was observed and described by two-ion energy transfer mechanism. The temporal evolution of upconversion luminescence was characterized by rise and decay times related to the dopant concentration.

Confirmation of temperature independence in the fluorescence lifetime of the 3P0 → 3F2 transition in praseodymium-doped fluoride glass

The dependence of the fluorescence lifetime from the 3P0→3F2 transition in praseodymium-doped fluoride glass as a function of dopant concentration and temperature was investigated. It was found that the fluorescence lifetime at the concentration of 7000ppm was constant with temperature, confirming the prediction of temperature independence in the lifetime for this transition in Pr3+-doped ZBLAN glass.

Multiple-wavelength up-conversion laser in Tm/sup 3+/-doped ZBLAN glass fiber

In this letter, we report on a multiple-wavelength up-conversion laser in Tm/sup 3+/-doped ZrF/sub 4/--BaF/sub 2/--LaF/sub 3/--AlF/sub 3/--NaF glass fiber pumped by an 1120-nm fiber laser. Single-wavelength, two-wavelength, and three-wavelength up-conversion lasers can be obtained by adjusting the distance between the coupler mirror and the fiber end, which is attributed to the frequency-filter effect in the etalon composed of the coupler mirror and the fiber end. The effects of the pump power on the performance of dual-wavelength laser were also discussed.

Analysis of up-converted UV fluorescence dynamics in Nd3+ doped ZBLAN glasses

In this work we investigate dynamics of the UV and violet fluorescence from the high lying 4 D 3 / 2 and 2 P 3 / 2 multiplets in Nd 3 + doped fluorozirconate (ZBLAN) glass. Emission properties of several samples with different neodymium ion concentrations (0.3-5 mol.%) were carefully examined under direct and multiphoton pulsed excitation and the dominant up-conversion mechanisms were proposed. The fluorescence lifetimes of the excited 4 D 3 / 2 and 2 P 3 / 2 levels were, according to our knowledge, for the first time determined. Additionally, the 4 D 3 / 2 and 2 P 3 / 2 luminescence quenching was analyzed by investigating the concentration dependencies of decay profiles.

Excited states Tm spectroscopy in ZBLAN glass for S-band amplifier

We report on excited state spectroscopy measurements of Tm doped ZBLAN glass designed for fiber amplifier in the 1.48 μm wavelength range. Low temperature absorption, emission and Excited State Excitation measurements are reported to clearly identify the transitions involved in the different pump mechanisms of this Thulium Doped Fluoride fiber Amplifier. Room and low temperature Excited State Absorption spectra were recorded and quantitative determination of absorption cross sections has been obtained which allows to further proceed to a modeling of this amplifier.

The effects of crystal-fields on the optical properties of Pr:ZBLAN glass

Absorption and emission spectra of Pr 3+-doped ZBLAN glass at room temperature were estimated from even- and odd-parity components of crystal-field parameters based on crystal-field theory and Judd–Ofelt theory. On the basis of point-charge approximation, the crystal-field parameters were obtained from structural models prepared by using molecular dynamics (MD) simulation. The calculated oscillator strengths for the 1D 2 and 3P J states were insufficient for the reproduction of the observed oscillator strengths for those states. These spectra were also estimated on the basis of the modified Judd–Ofelt theory, in which the variation of the energy difference between the 4f 2 and the excited 4f 15d 1 or 4f 15g 1 configurations were taken into account. It was found that the oscillator strengths increased and the values were comparable to the observed ones. The effect of the even-parity components of the crystal-field on the splitting of the energy levels and the rate of the forced electric-dipole transition were investigated. The contribution of the crystal-field and the energy variation of the 4f 2 configurations on the Judd–Ofelt intensity parameters was evaluated.

Spectroscopic properties and laser emission of Tm doped ZBLAN glass at 1.8 μm

A Tm doped ZBLAN glass is investigated to obtain a laser emission near 1.8 μm instead of classical crystalline host materials. After a brief description of the basic optical properties of Tm doped ZBLAN glass, demonstration of an efficient laser emission in the bulk material is presented. The other investigations are focussed on its wavelength tunability, its tolerance versus the pump wavelength and its behaviour in terms of thermal acceptance which are the main characteristics to consider in order to scale up such laser system.

Simulation of the optical properties of Er:ZBLAN glass

Absorption and emission spectra of Er 3+-doped ZBLAN glass at room temperature were estimated from structural models prepared by using molecular dynamics (MD) simulation based on crystal field theory and point-charge approximation. The calculated absorption and emission spectra substantially agreed with the observed ones. Furthermore, it was found that the emission spectra at low temperatures could be also reproduced to some extent. The relation between the splitting of the energy level and the crystal field parameters calculated from the Er 3+ ion in each structural model was examined. According to this relation, the energy levels could be classified into several groups. The splitting of the group represented by the 4 I 9/2 level was dominated by the short-range structure around the Er 3+ ions. The transition process for the measurement of the well-defined fluorescence line narrowing (FLN) spectrum was estimated from the characteristics of the splitting of the energy levels.

8.8 W diode-cladding-pumped Tm 3+ ,Ho 3+ -dopedfluoride fibre laser

A maximum output power of 8.8 W was generated from a diode-pumped Tm3+,Ho3+-doped ZBLAN glass fibre laser. The laser operated with a maximum slope efficiency of 36% with respect to the incident pump power. The wavelength was measured to be 2056 nm and some instability was observed in the output.

One-color one-beam pumping of Er^3+-doped ZBLAN glasses for a three-dimensional two-step excitation display

We demonstrate a one-color one-beam pumping method for a three-dimensional two-step excitation fluorescent display with Er(3+) -doped ZBLAN glass. A localized green fluorescent spot is obtained by use of a focused pump-light beam at 979 nm. The quantum efficiency of the two-step excitation fluorescence is investigated in a time-dependent analysis and an experiment with a pulsed pump light.

Avalanche assisted upconversion in Pr 3+ /Yb 3+ -dopedZBLAN glass

The author reports efficient upconversion optical pumping of the /sup 3/P levels of Pr/sup 3+/ in ZBLAN glass codoped with Yb/sup 3+/. Measurements of Pr/sup 3+/ visible emission against infrared pump intensity demonstrate the existence of an avalanche pumping process which comprises three components: radiationless energy transfer from Yb/sup 3+/ to Pr/sup 3+/, excited-state absorption in Pr/sup 3+/, and cross-relaxation between excited Pr/sup 3+/ ions and ground-state Yb/sup 3+/ ions.

Evanescent-field amplification in Nd3+-doped fluoride planar waveguide

Planar channel waveguides of rare-earth doped fluoride glass are demonstrated with single mode excitation and propagation losses below 3 dB/cm. The waveguide core was fabricated by Ag+–Na+ molten salt ion exchange process in a borosilicate glass (BGG31), and a Nd3+-doped ZBLAN glass was used as a cladding. A 0.45 dB signal amplification at 1.064 μm was observed in the fabricated 1 cm long waveguide, and a 0.9 dB amplification is expected at the emission peak (1.049 μm). Modeling results show 2.5 dB/cm potential gain with the improvement in surface flatness of ZBLAN glass.

Operation of diode laser pumped Tm/sup 3+/ ZBLAN upconversion fiber laser at 482 nm

Lasing at 482 nm is observed in Tm/sup 3+/-doped ZBLAN glass fiber pumped with single-mode InP semiconductor diode lasers. Up to 5 mW of 482 nm light is obtained with <40 mW of absorbed pump power from a single 1135 nm pump diode laser. The optimum pump wavelength is measured to be 1135-1340 nm. More efficient laser operation is observed in fiber with 2500 ppm Tm/sup 3+/ compared to 1000 ppm Tm/sup 3+/ because of the reduced length of the fiber laser cavity possible with increased doping. Improved slope efficiencies are also demonstrated when the fiber laser is co-pumped with up to 5 mW from a 1220 nm diode laser. The relative intensity noise (RIN) of the fiber laser displays a maximum of -90 dB/Hz at relaxation oscillation frequencies of a few tens of kHz. The measurement of RIN is limited by shot-noise of -152 dB/Hz above 2 MHz. At higher frequencies, self mode-locking was observed in the fiber laser, which may indicate the existence of saturable absorbers in the fiber core. The presence of such bleachable absorbers is indicated by the observed increase in threshold after upconversion lasing at 482 mm.

Up-conversion Luminescence in Er 3+- and Yb 3+-doped Fluorozirconate Glasses

Intense luminescence with up-conversion has been studied for E r3+- and Yb 3+-doped fluorozirconate glasses (ZBLAN). Effective infrared-to-visible conversion has investigated by pumping the glasses with radiation of InGaAs quantum well semiconductor laser at 980 nm. Luminescence has been observed in green (515-550 nm) for Er 3+-doped ZBLAN glasses. Intra- and intercenter processes and low efficient intracenter multiphonon interlevel relaxations were considered as mechanisms involved in the upconversion.

Crystallization behaviour of fluorozirconate glasses

Results are reported on crystallization modes in undoped ZBLAN and praseodymium doped ZBLAN glasses. The transformation usually proceeds from the surface with growth of oriented crystals. Activation energies of 154 and 216 kJ/mol were found for different crystallization stages at temperatures around 600 K.

Room temperature cw fibre laser at 3.5 μm in Er 3+ -doped ZBLAN glass

The first fibre laser operating above 3 μm at room temperature is reported. An Er3+-doped ZBLAN fibre pumped at 655 nm shows CW laser operation around 3.5 μm.

Co-doping effects in erbium 3+- and holmium 3+-doped ZBLAN glasses

Continuous wave (CW) operation of erbium 3+ (Er 3+)-, holmium 3+ (Ho 3−)- or thulium 3+ (Tm 3+)-doped ZBLAN fibre lasers, emitting at 2.7, 2.9 and 2.3 μm, is based on the depletion of their lower laser level by excited state absorption (ESA) of the appropriate selected pump wavelengths. This additional absorption process limits the efficiency of these laser transitions. The problem can be solved by the proper co-doping of the laser active dopants with other rare earth elements. It is shown that the desired depletion of the lower laser levels can be achieved in the case of Er 3+ and Ho 3+ by co-doping with Pr 3+ and Eu 3+.

Upconversion in Tm 3+-doped ZBLAN glasses

Upconversion emission spectra (at 650 nm excitation) and excitation spectra (from 620–680 nm) are presented for Tm-doped ZBLAN glasses. Two blue emission bands become apparent with maxima at 450 and 480 nm. The proposed upconversion mechanism explains the spectra and is in agreement with the observed quadratic dependence of the intensities of both emission bands with excitation power. Cross-relaxation processes, decreasing the upconversion efficiency, become active for Tm concentrations above 0.2 mol%.