Cr4+:Y3Al5O12 or Cr4+:YAG - is a material that can be used as an active media for CW, pulsed or self mode-locked tunable NIR solid-state lasers with tunability range 1340 - 1580 nm as well as a media for Q-switching in lasers with operating wavelength at 950 - 1100 nm. It is particularly useful in practical applications because of convenient absorption band of Cr4+around 1 mm which gives possibilities to pump it by regular Nd:YAG lasers. A saturation of absorption in the band at 1060 nm is useful for application in small sized Nd:YAG oscillators with flash lamp or laser diode pumping instead of based on dye or LiF:F-center passive Q-switches. Using the Cr4+:YAG crystal the self mode-locking (KML) regime is achievable. It gives an opportunity to build the laser source with pulse duration shorter then 100 fs at 1450 - 1580 nm. Finally, its high thermal and radiation stability as well as excellent optical and mechanical properties will give you an opportunity to design reliable devices based on the crystal.
      Gadolinium-scandium-gallium garnet doped with chromium and magnesium GSGG:Mg:Cr4+ is a material for passive Q-switching in 1 µm region. The valence state of chromium ion Cr4+ is provided by use of charge compensator. The crystals are grown by Zchochralski method in argon-oxigen atmosphere. Crystals of GSSS:Mg:Cr possessing the contrast parameter close to the one of YAG:Cr4+ have some advantages such as: possibility to provide necessary initial transmission at less thickness (typical thickness is about 1mm), transparency in the visible range which simplifies the alignment procedure.
      The crystals of Yttrium-Aluminum Garnet (YAG) doped with three-valence vanadium V3+ (V:YAG) in tetrahedral position suggest efficient q-switching for lasers operating in 1.3 µm region. The absorption band between 1.0 - 1.5 µm is attributed to 3A2 →3T2 transition of V3+ ion in tetrahedral position of garnet lattice. The crystals are grown by oriented crystallization method. Concentration of V3+ in tetrahedral position is controlled by growth and annealing conditions.The efficient q-switching of lasers operating at 1.3 micron has been obtained with a number of active mediums such as Nd:YAG, Nd:YVO4, Nd:KGd(WO4)2 under flash-lamp and laser diode pumping.
      Spinel crystal is a material having high optical damage threshold and low optical losses in 1.3 - 1.6 µm spectral range. Co2+-activated MgAl2O4 (Co:MALO, Co:spinel) can be used as a media for passive Q-switch of lasers which operate in the spectral range of 1.3 - 1.6 µm, for example 1.32 µm and 1.44 µm Nd:YAG lasers, 1.31 µm iodine lasers and especially 1.54 µm erbium glass lasers. High enough absorption cross-section of Co+2 ions together with practical absence of excited state absorption makes this material a very efficient passive Q-switcher (that does not require intracavity focusing) for various types of erbium glass lasers, including diode-pumped microchips.
      The new saturable absorber is based on NANOSIZED CRYSTALS IN GLASS MATRIX. It is transparent glass ceramics containing magnesium-aluminum spinel nanocrystallites doped with tetrahedrally coordinated Co2+ ions. The material provides q-switching within the spectral interval of 1200 - 1600 nm in particular for Yb-Er-glass laser (λ = 1.54 µm). Having the absorption cross-section of Co2+ at the wave length of 1.54 µm (transition 4A2 → 4T1(4F)) significantly higher than emission cross-section of Er:glass, it allows Q-switch operation without focusing radiation into the saturable absorber. In comparison with single crystals the glass ceramics is considerably cheaper. The glass ceramics technology is based on controlled nucleation and crystallization of the glass and has several advantages over conventional powder-processed ceramics as it uses glass preparation technique. They are: 1) ease of flexibility of forming in glassy state, 2) uniformity of microstructure, 3) reproducibility of properties that results from starting glass.

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