The Study On Characteristics Of All Solid-state Mid-infrared Two Micrometer Lasers

The 2 μm laser is "eye-safe" laser, which is located at the well-known "molecular fingerprint" spectra region, has significant applications in the field of environment monitoring, remote communication, material processing, medicine, metrology and military. On the other hand, the 2 μm laser systems also can be used as pump sources of mid- and far- infrared laser systems such as Cr2+:ZnSe and Cr2+:ZnS mid- infrared lasers, as well as OPOs based on ZnGeP and LiInS for achiving mid-and far-infrared laser in 3-5 μm and 8-12 μm wavelength region. Due to the wide applications, the 2 μm lasers have drawn a lot of attentions in recent years.In this paper, the theory analysis and experimental studies of Tm3+ doped and Tm3+, Ho3+ co-doped bulk lasers operating in continue-wave、wavelength tunable、 Q-switching and mode-locking regimes have been presented. By using a birefringent quartz plate as wavelength selector, the wavelength tunable properties of Tn:LSO, Tm:SSO, and Tm:LiTaO3 lasers have been investigated. By employing a two dimensional AO modulator, the Q-switched Tm:LSO, Tm:SSO, and Tm:LiTaO3 laser have been realized. With Graphene and SWCNT as saturaber absorbers, passively Q-switched Tm:LSO, Tm:LiTaO3, and Tm:LuAG lasers have been realized. With Tm:LuAG as gain material, based on the SESAM, a watt-level all-solid-state mode-locked 2μm laser was obtained.Ⅰ. The basic structure of birefringence quartz plate together with its mechanism for wavelength selecting in 2 μm spectral regions has been analyzed. The study indicated that the birefringent quartz plate possesses the advantage of simple design, high damage threshold, broader wavelength tunable range as well as high stability.Ⅱ. By using the birefringent quartz plate, the tunable lasing properties of Tm:LSO, Tm:SSO, and Tm:LiTaO3 crystal have been studied. The corresponding tuning ranges were 145 nm (1936.0 nm-2081.9 nm)、100 nm (1923.9 nm-2023.8 nm) and 160 nm (1835 nm-1995 nm). The experimental results indicated that the birefringent quartz plate holds the advantage of high tuning precision and broad tuning range which is very suitable for 2 μm Tm3+ doped all-solid-state broadband spectrum lasers.III. The basic principle of two-dimensional AO modulator has been investigated. Compaped with the one-dimensional AO modulator, two-dimensional AO modulator possesses much stronger turn-off ability. The two-dimensional AO modulator could take full advantage of the quality factor of the fused quartz, achieving a larger diffractional loss with a lower ultrasonic power. In 2 μm spectral region, only 1/4～1/5 ultrasonic power was required to achieve a comparative diffraction loss which was achieve by one-dimensional AO modulator.IV. By using a two-dimensional AO modulator, the active Q-switched Tm:LSO、 Tm:SSO and Tm:LiTaO3 lasers were realized. A minimum pulse duration of 345 ns was obtained from the Tm:LSO laser, corresponding to a single pulse energy of 0.26 mJ and peak power of 0.75 kW. In Tm:SSO laser, the obtained minimum pulse duration is 308 ns, corresponding to a single pulse energy of 128 μJ and peak power of 416 W. In Tm:LSO laser, a minimum pulse duration of 244 ns was achieved, corresponding to a single pulse energy of 0.42 mJ and peak power of 1.65 kW.V. The physical structure of SWCNT has been detailed described together with its optical absorption and saturable absorption mechanisms. The thermal conduction behaviors and fabrications method of SWCNT saturable absorber have been stated. The studies have shown that the optical absorption of SWCNT is associated with the chirality and diameter of SWCNT, the broad band saturable absorbers can be obtained by combining different chirality and diameter SWCNTs. Besides, the studies indicated that the SWCNT saturable absorber possess the advantage of large thermal conductivity, easy fabrication as well as low cost.VI. By using SWCNT as saturable absorber, stable Q-switched Tm,Ho:YAP, Tm:LiTaO3 and Tm:LuAG lasers were realized. The minimum pulse duration of 245 ns and 135 ns were achieved at 2128.3 nm and 2130 nm from α-cut Tm,Ho:YAP and b-cut Tm,Ho:YAP laser, respectively. A minimum pulse duration of 560 ns was achieved from Tm:LiTaO3 laser, the corresponding single pulse energy and peak power were 10.1 μJ and 34.2 kHz. The Tm:LuAG laser produced a minimum pulse duration of 405 ns at 2021.6 nm, while the maximum single pulse energy is 40.6 μJ at 2019.7 nm, corresponding to a maximum average output power of 1.9 W.Ⅶ. The structures of lattice and band of Graphene have been studied together with its optical absorption and saturable absorption mechanisms. The studies have shown that Graphene has a unique zero-band structure which enables it could absorb light at any wavelength region. Due to its large thermal conductivity, the Graphene possesses a high damage threshold. Besides, the large modulation depth and easy of fabrication make it very attractive for 2 μm saturable absorbers.Ⅷ. The large-area Graphene was grown by using the CVD method with a thickness of 1-2 layers. The graphene saturable absorber mirror at 2 μm was fabricated by transferring the Graphene on a 2 μm high reflective mirror. With the Graphene SAM as a Q-switcher, stable Q-switched Tm:LSO laser was achieved. At the maximum absorbed pump power of 3.4 W, minimum pulse duration of 7.8 μs was obtained at 2030.8 nm, the corresponding pulse repetition rate was 7.6 kHz and single pulse energy is 14.0 μJ.Ⅸ.The methods for achieving 2 μm mode-locking lasers were detailed analyzed. The basic mechanisms and physical process of SESAM mode-locking were investigated. The condition of SESAM mode-locking without Q-switching instabilities has been analyzed. By using a SESAM, continue wave mode-locking Tm:LuAG laser was achieved at 2022.9 nm, corresponding to a pulse duration of 38.4 ps and pulse repetition rate of 129.2 MHz.The main innovations of this dissertation are as follow:Ⅰ. By using the birefringent quartz plate, the tunable lasing properties of Tm:LSO, Tm:SSO, and Tm:LiTaO3 crystal have been studied. The corresponding tuning ranges were 145 nm (1936.0 nm-2081.9 nm)、100 nm (1923.9 nm-2023.8 nm) and 160 nm (1835 nm-1995 nm). The studies have shown that Tm:LiTaO3 laser possesses much higher average output power and broader wavelength tunable range, which is more suitable for 2μm broadband wavelength tunable operations.Ⅱ. By using a two-dimensional AO modulator, the active Q-switched Tm:LSO、 Tm:SSO and Tm:LiTaO3 lasers were realized. A minimum pulse duration of 345 ns was obtained from the Tm:LSO laser, corresponding to a single pulse energy of 0.26 mJ and peak power of 0.75 kW. In Tm:SSO laser, the obtained minimum pulse duration is 308 ns, corresponding to a single pulse energy of 128 μJ and peak power of 416 W. In Tm:LiTaO3 laser, a minimum pulse duration of 244 ns was achieved, corresponding to a single pulse energy of 0.42 mJ and peak power of 1.65 kW. The studies have shown that Tm:LiTaO3 crystal possess an excellent energy storage ability, which is more suitable for realizing short pulse, high pulse energy and high peak power Q-switched lasers.Ⅲ. The passively Q-sitched Tm,Ho:YAP, Tm:LiTaO3, Tm:LuAQ Tm:LSO and Tm:SSO lasers were realized. The minimum pulse duration of 245 ns and 135 ns were achieved at 2128.3 nm and 2130 nm from a-cut Tm,Ho:YAP and b-cut Tm,Ho:YAP laser, respectively. A minimum pulse duration of 560 ns was achieved from Tm:LiTaO3 laser, the corresponding single pulse energy and peak power were 10.1 μJ and 34.2 kHz. The Tm:LuAG laser produced a minimum pulse duration of 405 ns and a maximum average output power of 1.9 W. A minimum pulse duration of 7.8 μs was obtained from Tm:LSO laser, corresponding to a single pulse energy of 14.0 μJ and a pulse repetition rate of 7.6 kHz. The studies have shown that the Tm,Ho:YAP crystal is more favourable for attaining short pulse with high pulse repetition rate while the Tm:LuAG crystal is more suitable for realizing much higher laser output and single pulse energy.IV. By using a SESAM, continue wave mode-locking Tm:LuAG laser was achieved at 2022.9 nm with a maximum average output power of 1.21 W, corresponding to a pulse duration of 38.4 ps and pulse repetition rate of 129.2 MHz.