Passive Q-switching of erbium glass laser by magnesium aluminosilicate sitall with cobalt ions

Abstract

We have studied the radiation output parameters for an erbium glass laser, lasing at a wavelength of 1.54 µm, with passive Q-switching by means of a cobalt-containing magnesium aluminosilicate sitall compared with a saturable absorber based on a magnesium aluminum spinel crystal with cobalt ions. We have shown that the output characteristics of the laser emission when using sitall are not inferior to the analogous characteristics of a laser based on a spinel crystal, and are practically independent of the temperature of the saturable absorber in the range 0 o C-80 o C. The duration (energy) of the output pulses was 70 nsec (~4 mJ), the energy dispersion of the radiation pulse relative to the average value was no greater than 3%, the beam divergence was 2.8 mrad, the laser beam quality factor was M 2 = 1.2.Key words: Q-switching, erbium glass laser, Co 2+ ion, magnesium aluminum spinel, aluminosilicate sitall.Introduction. In recent years, considerable attention has been focused on designing laser radiation sources in the 1.5 µm region. Radiation with this wavelength falls within the transparency range of the atmosphere and is eyesafe, which means that the prospects are good for using these lasers in range finders, target acquisition systems, systems for remote probing of the atmosphere, data transmission and processing. This is why it is important to develop a stable and efficient source of laser radiation that lases in this spectral range.For the applications indicated above, we need nanosecond radiation pulses with high peak power. Such pulses can be obtained by operating the laser in passively Q-switched mode. Today the most efficient passive gate for erbium glass lasers, lasing at a wavelength of 1.54 µm, is a magnesium aluminum spinel containing divalent cobalt ions (Co 2+ :MgAl 2 O 4 ) [1][2][3][4]. In this material, the Co 2+ ions occupy positions with tetrahedral coordination and have a large ground state absorption (GSA) cross section (σ GSA ≈ (3-5)⋅10 -19 cm 2 ), a rather long bleaching relaxation time (τ = 300-400 nsec), and low excited state absorption (ESA) (σ ESA /σ GSA < 0.05) [1,4]. At the same time, it has been demonstrated [5][6][7] that materials in the form of transparent glassceramic (sitall) containing divalent cobalt ions can be used as passive gates for lasers in the spectral range 1.3-1.6 µm. It has been established that during synthesis of aluminosilicate sitall, a microcrystalline spinel phase is formed in it where the Co 2+ ions are found in tetrahedral coordination. This provides it with the optical characteristics needed for laser applications [8][9][10]. In particular, in the 1.5 µm region, sitalls with Co 2+ ions have ground state absorption and excited state absorption (GSA and ESA) cross sec-

Saturable absorbers based on tetrahedrally coordinated transition-metal ions in crystals (Review)

“…It reached 19% of the free generation pulse energy [242]. A comparison of operation under identical conditions of PS based on Co 2+ :MgAl 2 O 4 crystal and Co 2+ :MAS sitall showed that the materials had similar emission radiation characteristics when used in an Er laser (energy and duration of a single pulse, scatter of these parameters with long-term operation of the laser and over a broad temperature range, M 2 -factor) [243]. TC Co 2+ ions in ZnSe and ZnS crystals are also know as PS for Er lasers.…”

“…However, Co 2+ ions in them exhibit anisotropic nonlinear absorption Al 5 O 12 crystals, must be placed appropriately in the laser cavity[232]. Sitalls with crystalline spinel phases and Co 2+ ions incorporated in them can also be used for gain modulation of Er lasers in the spectral region 1.5 μm[121,123,235,[241][242][243]. Emission pulses of duration 100 nsec and energy 7 mJ in a glass Er laser with lamp pumping were recorded using sitalls with Co 2+ :ZnAl 2 O 4 (Co…”

Effect of La2O3 on the physical and crystallization properties of Co2+-doped MgO–Al2O3–SiO2 glass

“…Transition-metal (TM) ion doped glass-ceramics have attracted much interest in recent years, due to their broad range of potential applications, such as photonic devices, ultra-broadband luminescence, and saturable absorbers [2][3][4][5]. In the past decade, transparent GCs with tetrahedral Co 2+ ions containing nanocrystals have been used successfully as passive Q-switchers for 1.3 μm and 1.54 μm lasers [6,7]. They even have better Q-switch performances than Co 2+ -doped crystals.…”

“…Co 2+ -doped GCs are prepared by sol-gel technique [4,11,12] or conventional method [6][7][8][9][10]. The advantages of the sol-gel method, as compared with conventional one, are mainly preparation of hybrid materials and low temperature processing [4,11,12].…”

Formation of Co2+-doped nanocrystals in La2O3–MgO–Al2O3–SiO2 glass-ceramics

“…The GCs are more cost efficient than their single-crystal counterparts because of their faster fabrication process and possibility of mass production. During the past few years, transparent GCs with tetrahedral Co 2+ ions containing nanocrystals have been used successfully as passive Q-switchers for Er:glass laser [3,8,9]. They even have better Qswitch performances than Co 2+ -doped crystals [3].…”