Research On Dual-Wavelength Lasers And New Sodium Lasers Based On Crystal Stimulated Raman Scattering

Stimulated Raman scattering (SRS) is an effective method to generate new wavelengths based on frequency conversion. SRS belongs to the third-order nonlinear optical effect. In recent years, the crystal Raman lasers based on SRS have made great progress with a large number of research results. Thanks to the technologies in three areas: Firstly, the Raman crystals with good quality of were invented and the growth process was mature. Secondly, optical coating technology has made progress and coating accuracy has been improved. Thirdly, LD-pumped with high-performance has been developed and industrialized. All of these provide a strong technical support for the development of the efficient crystal Raman laser. Currently, the laser spectrum with crystal Raman laser can extend from the ultraviolet to the near infrared by using SRS sources and SRS combined with other non-linear laser. In this thesis, two specific applications for the study of the background are solid state lasers emitting dual-wavelength with quite small wavelength separation and 589 nm sodium lasers. They will be realized by means of crystal Raman laser. First, solid state lasers emitting dual-wavelength simultaneously have many important applications in dual-wavelength laser probe, two wavelengths interferometer, spectral analysis, holography, medical instrumentation, differential lidar, and terahertz (THz) wave difference frequency generator. The first type is the laser involving two different laser transitions with a large wavelength separation, such as 1.06 and 1.3 μm dual-wavelengths. The second type is the laser operating in the same laser transition with a small wavelength separation, which is very attractive for THz generation by nonlinear difference frequency mixing, such as 1.319 and 1.338 μm dual-wavelengths. Our study focuses on the latter type. Traditionally, the methods to realize dual-wavelength laser with small wavelength separation are designing a typical coating for the output coupler to appropriately choose the transmission values of the two wavelengths, or using an intracavity etalon as a wavelength tuning element. The work cited above focused on the fundamental laser frequency in neodymium host crystals. Compared with fundamental Nd lasers, SRS lasers provide pulse duration shortening, beam quality improvement, Raman beam cleanup, without phase-matching, purer spectrum. Three designs of the dual-wavelength lasers based on the crystal Raman laser are as follows:(1) 1st-Stokes and 2nd-Stokes dual-wavelength operation Raman laser; (2) Two Raman crystals with different Raman frequency shifts are employed to generate first Stokes at two different wavelengths; (3) Dual-wavelength operation Raman laser based on the dual-wavelength fundamental laser. Second,589-nm light sources at the sodium D2 line have attracted increased attention in recent years. These light sources have been required by many applications, such as medicine, biology, communications, display technology, lidar measurement in the atmosphere, and for creating guide stars through resonance fluorescence in the mesosphere sodium layer. In recent years, researchers have begun to focus on crystalline Raman lasers to obtain 589 nm lines. In order to achieve this purpose, the precise wavelength of the fundamental frequency laser and the precise Raman frequency shift of the Raman crystal are inevitable. In this thesis, we focus on the novel molybdate BaTeMo2O9 (BTM) and KLu(WO4)2 (KLW) crystals for the intracavity frequency-doubled Raman laser emitting at 589 nm.The main contents of this thesis are as follows:1. 1st-Stokes and 2nd-Stokes dual-wavelength operation within a diode-side-pumped Q-switched intracavity Raman laser was realized. Using an Nd:YAG ceramic gain medium, an BaW04 Raman medium, an output coupler of the transmission of 3.9% at 1180 nm and of 60.08% at 1325 nm, the maximum output power of 8.30 and 2.84 W at a pulse repetition rate of 15 kHz for the 1st Stokes and the 2nd Stokes laser were obtained, respectively. The corresponding optical conversion efficiency from diode laser to the 1st Stokes and 2nd Stokes laser are 5.0%and 1.4%, respectively. With the pump power of 209 W and a pulse repetition rate of 15 kHz, the 1st Stokes and the 2nd Stokes pulse widths were 20.5 ns and 5.8 ns, respectively.2. A diode-side-pumped^-switched second-Stokes laser emitting at 1322 nm employing Nd:Gd3Ga5O12 as gain medium and BaW04 as Raman medium was realized. With a pump power of 125 W and pulse repetition rate of 20 kHz, a maximum second-Stokes output power of 3.8 W was obtained. The corresponding diode-to-second-Stokes conversion efficiency was 3% and the second-Stokes pulse width was 9.2 ns.3. Dual-wavelength laser operation by means of two Raman crystals (self-Raman crystal and Raman crystal) with different Raman frequency shifts. A diode-pumped actively 0-switched Nd-doped yttrium orthovanadate self-Raman emission at 1175 nm and undoped gadolinium orthovanadate Raman emission at 1174 nm dual-wavelength laser is demonstrated. With the pump power of 20.5 W and pulse repetition frequency of 20 kHz, the maximum dual-wavelength output power of 1.52 W was obtained, which contained a 0.71 W 1174 nm Raman laser component and a 0.81 W 1175 nm self-Raman laser component. The corresponding dual-wavelength Raman pulse width was 14.8 ns.4 A diode-pumped actively Q-switched Nd:YVO4 self-Raman emission at 1524 nm and undoped GdVO4 Raman emission at 1522 nm dual-wavelength laser is demonstrated. With the pump power of 21.5 W and pulse repetition frequency of 20 kHz, the maximum dual-wavelength output power of 1.62 W was obtained, which contained 0.54 W 1522-nm Raman laser component and 1.08 W 1524-nm self-Raman laser component. The corresponding dual-wavelength Raman pulse width was 5.6 ns. Experimental results indicated the dual-wavelength Raman laser with quite small wavelength separation was effective through simultaneous self-Raman and Raman shift.5. Dual-wavelength laser operation has been realized by means of the crystal SRS in dual-wavelength fundamental laser. A diode-pumped, actively Q-switched dual-wavelength Raman laser at 1177 and 1180 nm employing ceramic Nd:YAG as gain medium and BaWO4 as Raman medium is demonstrated. The dual-wavelength Raman laser emission at 1177 and 1180 nm is based on the dual-wavelength fundamental laser emission at 1061 and 1064 nm. With a pump power of 18.5 W and pulse repetition frequency of 20 kHz, a maximum dual-wavelength output power of 1.9 W was obtained, comprising a 0.6 W,1177 nm laser component and a 1.3 W,1180. nm laser component. The second-Stokes dual-wavelength Raman laser emission at 1321 and 1325 nm is based on the dual-wavelength fundamental laser emission at 1061 and 1064 nm. With a pump power of 18.4 W and pulse repetition frequency of 15 kHz, a maximum dual-wavelength output power of 1.67 W was obtained, comprising a 0.75 W,1321 nm laser component and a 0.92 W,1325 nm laser component. And the fundamental, first-Stokes and second-Stokes dual-wavelength pulse widths were 10.4, 4.5 and 2.9 ns, respectively. The M2 factors of the second-Stokes dual-wavelength Raman beam were measured to be 1.4 and 1.5 in the horizontal and vertical directions, respectively.6 A diode-pumped, actively Q-switched eye-safe dual-wavelength laser employing ceramic Nd:YAG as gain medium and BaWO4 as Raman medium is demonstrated. The dual-wavelength Raman laser emission at 1502 and 1527 nm is based on the dual-wavelength fundamental laser emission at 1319 and 1338 nm. With a pump power of 17.3 W and pulse repetition frequency of 20 kHz, a maximum dual-wavelength output power of 0.82 W was obtained, comprising a 0.37 W,1505 nm laser component and a 0.45 W,1527 nm laser component.7 A diode-side-pumped, actively Q-switched eye-safe dual-wavelength laser employing crystal Nd:YAG as gain medium and BaWO4 as Raman medium is demonstrated. The dual-wavelength Raman laser emission at 1502 and 1527 nm is based on the stimulated Raman scattering action of the dual-wavelength fundamental laser emission at 1319 and 1338 nm. With the pump power of 125 W and pulse repetition frequency of 5 kHz, the maximum dual-wavelength output power of 2.3 W was obtained, comprising a 1.4 W,1505 nm laser component and a 0.9 W,1527 nm laser component.8. The compact simultaneous actively Q-switched and mode-locked (QML) Raman laser is demonstrated due to the wider spectral width and the SRS nonlinear process. A single wavelength Raman laser employing Nd:KLu(WO4)2 as gain medium and BaWO4 as Raman medium with high mode-locking repetition-rate is demonstrated. The picosecond first Stokes at 1549 nm based on the fundamental laser emission at 1355 nm is realized. With an absorbed pump power of 14.6 W and pulse repetition frequency of 20 kHz, a maximum output power of 1.4 W. The stable QML of Raman laser was obtained at the absorbed pump power of about the threshold to 10 W, the mode-locking pulse repetition rate of 1.6 GHz is obtained; the corresponding mode-locking pulse width is approximate 28 ps.9 A dual-wavelength QML Raman laser employing Nd:CNGG as gain medium and BaWO4 as Raman medium is demonstrated. The dual-wavelength Raman laser emission at 1173 and 1175 nm is based on the stimulated Raman scattering action of the dual-wavelength fundamental laser emission at 1059 and 1061 nm. With the pump power of 14 W and pulse repetition frequency of 5 kHz, a maximum output power of 190 mW, the corresponding conversion efficiency was about 1.4%. The stable QML of Raman laser was obtained at the absorbed pump power of about the threshold 3.5 to 7 W, the pulse width of the Q-switched envelope was about 8.7 ns and the corresponding mode-locking pulse width was approximate 450 ps.10.589 nm Raman laser schemes based on the separate laser material and Raman material combinations of Nd:YAG/BaTeMo2O9 and Nd:YAG/KLu(WO4)2. A frequency-doubled BaTeMo2O9 Raman laser is realized inside an acousto-optically Q-switched Nd:YAG laser end-pumped by a fiber-coupled diode laser. The BaTeMo2O9 crystal generates the first-Stokes laser at 1178 nm, and intracavity second-harmonic generation is accomplished to generate the 589 nm emission. Under an incident diode power of 16.6 W and a pulse repetition frequency of 20 kHz, the 589 nm laser power of 0.39 W was obtained, corresponding to a diode-to-yellow laser conversion efficiency of 2.3% and pulse duration of 4.1 ns. The linewidth was about 0.1 nm and the M2 factors are measured to be 1.6 and 1.4 in the horizontal and vertical directions, respectively.11 An intracavity frequency-doubled Raman laser emitting at 589 nm by using a KLu(WO4)2 Raman medium was realized within a diode-side-pumped Q-switched Nd:YAG laser. Under an incident diode power of 125 W and a pulse repetition rate of 10 kHz, the 589.3 nm power of 4.33 W was obtained, corresponding to a diode-to-yellow laser conversion efficiency of 3.5% and a minimum pulse width of 38 ns. The linewidth was about 0.2 nm and the M2 factors are measured to be 4.9 and 5.0 in the horizontal and vertical directions, respectively.The main innovations of this thesis are as follows:1. 1st-Stokes and 2nd-Stokes dual-wavelength stable operation in diode-side-pumped Nd:YAG/BaWO4 Raman laser was presented for the first time. The maximum output power of 8.30 W and 2.84 W at a pulse repetition frequency (PRF) of 15 kHz for 1st Stokes and 2nd Stokes wave were obtained, respectively. These are the highest Raman output powers at about 1st-Stokes and 2nd-Stokes obtained from a intracavity crystalline Raman laser.2. Dual-wavelength lasers by means of two Raman crystals with different Raman frequency shifts have been proposed for the first time. The method presented in this thesis can be extended to other wavelengths and Raman crystals lasers. Nd:YVO4 is employed as a self-Raman crystal and undoped GdV4O is employed as a Raman crystal, the dual-wavelength operation is realized at 1522 nm and 1524 nm based on GdVO4 Raman frequency shift (Stokes shift being 882 cm-1) and Nd:YVO4 self-Raman frequency shift (Stokes shift being 889 cm-1) in 1342 nm Nd:YVO4 fundamental laser.3. Cascaded-Stokes dual-wavelength laser operation has been realized by means of SRS in dual-wavelength fundamental laser for the first time. Cascaded-Stokes dual-wavelength operation at 1321 and 1325 nm BaWO4 Raman laser based on the dual-wavelength ceramic Nd:YAG fundamental laser at 1061 and 1064 nm has been realized.4. Diode-side-pumped eye-safe dual-wavelength Raman laser has been realized for the first time. With the pump power of 125 W and pulse repetition frequency of 5 kHz, the maximum dual-wavelength output power of 2.3 W was obtained, comprising a 1.4 W, 1505 nm laser component and a 0.9 W,1527 nm laser component.5. Simultaneous Q-switching and mode locking of the dual-wavelength Stokes laser employing Nd-doped Ca3(NbGa)2-xCa3O12 (Nd:CNGG) crystal with particular spectral parameters as gain medium and BaWO4 as Raman medium is demonstrated for the first time. The dual-wavelength Raman laser emission at 1173 and 1175 nm is based on the stimulated Raman scattering action of the dual-wavelength fundamental laser emission at 1059 and 1061 nm. With the pump power of 14 W and pulse repetition frequency of 5 kHz, a maximum output power of 190 mW. The stable QML of Raman laser was obtained at the absorbed pump power of about the threshold 3.5 to 7 W, the pulse width of the Q-switched envelope was about 8.7 ns and the corresponding mode-locking pulse width was approximate 450 ps.6. An intracavity frequency-doubled BaTeMo2O9 Raman laser is realized inside an acousto-optically Q-switched Nd:YAG laser end-pumped by a fiber-coupled diode laser for the first time.7. An intracavity frequency-doubled Raman laser emitting at 589 nm by using a KLu(WO4)2 Raman medium was realized within a diode-side-pumped Q-switched Nd:YAG laser for the first time.