Fluoride glasses: lasers

Nd3+ ions are by far the most widely investigated ions in all types of materials, essentially because of the ideal, 4-level, 1.06 m laser transition from 4F3/2 to 4In/2 shown in Fig. 5. Thus, the spectroscopic properties of Nd3+ ions are reported for a large number of different compositions of fluorozirconate, fluoroindate, fluorohafnate, fluoroaluminate and other kinds of fluoride glasses [31,36,63-69]. 

Lasing has been demonstrated at 1.06 /tm in Nd3+-doped ZBLAN and BIG fluoride glass rods pumped by an alexandrite laser and xenon flashlamps, respectively [71,72], Fig. 6 shows the 1.06 //m laser output energy out of Nd3+-doped and Cr3+ Nd3+-codoped fluoroindate glass rods of 40 mm length. In presence of Cr3+ ions, which are efficient absorbers of excitation light from flashlamps,... 

The violet, green and red emissions of Er3+ ions in fluoride glasses can also be obtained with excitation at 650nm and 1.48 /xm, which are other spectral domains where laser diodes are commercially available. Violet and green emissions are obtained through a 2-step 650 nm up-conversion process, while four and three steps are required with 1.48 /an pumping [105,106], Excitation at 980 nm into 4In/2 may initiate two-step up-conversion and consequent green and red emissions [107],... 

Little basic research has been devoted to Yb3+ ion itself which possesses only one excited state [151]. However, as shown previously, this ion is of special interest for a number of energy transfer and up-conversion processes, which take advantage of the strong 2F7/2 — 2F5/2 absorption band of Yb3+. In addition, efficient lasing around 1.02 can be obtained with this ion and laser cooling effects have been observed. These points are developed in the next section devoted to applications of rare-earth-doped fluoride glasses. 

Characteristics of rare-earth-doped ZBLAN fluoride glass fiber lasers, (i) incident, (1) launched, and (a) absorbed pump powers, (uc) up-conversion pumping... 

Because of the wide transmission range and low phonon energies of fluoride glasses, the observation of numerous rare-earth laser lines is possible at wavelengths beyond 2 fim, where the transmission of silica fibers is extremely poor. Laser sources around 2 /jm are of special interest because they belong, not only to the eye-safe spectral domain, but also to an optical transparency window of the atmosphere. Two fluoride glass fiber lasers have been demonstrated in that region. First, a Ho3+ laser with the 5I7 -> 5I8 transition at 2.024 /on which delivers 250 mW with 60%... 

Characteristics of fluoride glass optical amplifiers. All fibers are ZBLAN-based glass except when otherwise indicated. (LD) laser diode ( ) gain obtained with two amplification units. 

Another very promising fabrication process of fluoride glass channel waveguides has been investigated by Davis et al. [256], This process is based on the possibility to create photo-induced modification of the refractive index by a focused, femtosecond IR laser beam. Linear, transparent and colorless marks were formed in the inside of the glass sample translated relatively to the laser beam. Similar experiments were conducted with UV irradiation of PZG fluoride glass thin films [257]. 

Rare-earth-doped fluoride glasses are suitable for some other specific applications that require laser transitions at wavelengths greater than 2 pm, efficient up-conversion mechanisms or ultra-high quantum efficiencies. 

An interesting polymeric structure, based on octahedrally coordinated cations corner-linked to each other by shared anions, results from a similar increase of cation size in an initially molecular MX4 liquid. Such structures, and their more cross-linked relatives with still higher coordination numbers consequent on smaller anion-cation radius ratios, are no doubt fundamental to the new class of fluoride glasses based on Zrp4 and Hfp4, which are currently a focus of attention in laser and infrared transmission line technology. ... 

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