Font Size: a A A

Investigation On The OPO And SRS Characteristics Pumped By All-solid-state Q-switched And QML Lasers

Posted on:2017-03-25Degree:DoctorType:Dissertation
Country:ChinaCandidate:H W ChuFull Text:PDF
GTID:1108330485982247Subject:Optical Engineering
Abstract/Summary:PDF Full Text Request
Since the first demonstration of nonlinear frequency conversion in 1961 by Franken et al. using quartz crystal (SiO2) to double the frequency of the Ruby laser at 694.3 nm into the ultraviolet spectral range, it has been one of the hotspot research directions in the laser physics. Nowadays, nonlinear frequency conversions are one of the most reliable and efficient technologies to convert the common lasing wavelengths to another novel spectral band. Second order frequency conversions (three-wave interaction), such as second harmonic generation (SHG), sum-frequency generation (SFG), different frequency generation (DFG) and optical parametric oscillator (OPO), and third order frequency conversion (four-wave interaction), such as four-wave mixing (FWM), third harmonic generation (THG), stimulated Raman scattering (SRS) and stimulated Brillouin scattering (SBS), have been well and common studied in recent years. Among these nonlinear frequency conversions, nonlinear frequency downconversion technology, such as DFG, OPO and SRS, are an efficient tool to obtain mid-infrared (MIR) spectral sources. In this dissertation, I will focus on two frequency downconversion technologies, i.e. OPO and SRS and their combination.In this dissertation, I have realized some experiment and theoretical simulations, for example, using Q-switched, doubly Q-switched and Q-switched dual-wavelength lasers as pumping sources, I realized simultaneous OPO and SRS processes in a single KTP crystal, and I also established a set of coupled rate equations to theoretically analyze the nonlinear frequency downconversions, the numerical simulations fitted well with the experimental data; using KLM and dual-loss-modulated QML lasers as pumping sources, I demonstrated for the first time the KTP IOPO with subnanosecond pulse duration. Considering the fluctuations of QML laser, I theoretically simulated the experimental results, and the modelling was found to be suitable for the KLM/QML lasers pumped IOPO. I reported a Yb:YAG/KTP Raman laser with the third Stokes radiation at 1150 nm for the first time, the fundamental wavelength was 1050 nm and the pulse duration for the third Stokes line was 764 ps. The efficient Raman gain coefficient of KTP was estimated as 2.1 cm/GW. Using the ferroelectric material Nd,MgO:LiNbO3 as the gain crystal, a 1.47 W a-polarized laser at 1094 nm was demonstrated for the first time. As an application, a KTP IOPO pumped by this laser was realized with a signal wavelength at 1630 nm and a peak power of 11.4 kW, which was 3 times higher than the previous one. The main aspects of this dissertation are as following:1. Using Nd,MgO:LiTaO3 crystal as the gain medium, and the monolayer graphene as the saturable absorber for the first time, we realized the dual-wavelength Q-switched Nd,MgO:LiTaO3 laser at 1082 and 1092 nm. The minimum pulse duration was measured as 176 ns with a maximum pulse energy of 2.75 μJ.2. We firstly demonstrated the dual- and multi-wavelength Q-switched and mode-locked Nd:GGG laser. The modulation depth was found to be nearly 100%, while the mode-locking pulse duration was estimated to be 908 ps.3. Using a fiber coupled laser diode (LD) at 808 nm as a pump source, I realized a Cr4+:YAG Q-switched Nd:GGG laser pumped KTP multi-frequency-downconversions, i.e. simultaneous SRS and OPO. Under an LD incident pump power of 10.5 W, the maximum signal output power was 302 mW with a minimum pulse duration of 1.61 ns, while the maximum Stokes output power was 115 mW with a minimum pulse duration of 2.88 ns. The second Stokes and the third Stokes radiations were 1124.9 and 1160.7 nm. The corresponding optical-to-optical conversion efficiencies were 2.88% and 1.1%, with a total conversion efficiency of 3.98%. The beam quality factor M2 was found as 1.2.4. In order to compress the signal pulse duration and improve the signal peak power, a dual-loss modulation was induced in this dissertation. Simultaneous SRS and OPO in a single KTP crystal were also realized, with a minimum single pulse duration of 580 ps and a peak power of 43.7 kW. Adjusting the angle of the KTP, a Raman shift of 154 cm-1 was reported for the first time.5. Using Cr4+:YAG Q-switched dual-wavelength Nd:LGGG laser as the pumping source, an intracavity KTP multi-frequency-conversion was demonstrated. Dual-wavelength operation of the Stokes and signal waves was also realized. The maximum output power of the signal beam is 448 mW with a minimum pulse duration of 850 ps. A set of coupled rate equations on the basis of the Q-switched dual-wavelength laser was also established. The numerical simulations agreed with the experimental results more or less.6. We first demonstrated the W-level output from an LD pumped c-cut Nd,MgO:LiNbO3 crystal. The maximum output power was 1.47 W for the CW operation at the a polarization at 1094 nm. As an application, a KTP IOPO pumped by the actively Q-switched Nd,MgO:LiNbO3 laser at 1094 nm was also realized. The signal output power was 96 mW, and the minimum pulse duration was 1.69 ns at an AOM modulation rate of 5 kHz, corresponding to a maximum peak power of 11.4 kW.7. Using a 940 nm LD pumped Yb:YAG laser at 1050 nm as the OPO fundamental wave, we realized a Yb:YAG/KTP Raman laser both in CW and Q-switched operations. In Q-switched regime, a maximum total output power was 666 mW under an incident pump power of 22 W with a pulse repetition rate of 9.8 kHz. The third Stokes radiation at 1148.4 nm has a minimum pulse duration of 764 ps, corresponding to a maximum pulse energy of 13 μJ and a peak power of 17.1 kW. Anti-stokes radiation has a pulse duration of 1.54 ns with a peak power of 3.5 kW. The beam quality factors for the total beam were 1.64 and 1.48, indicating Stokes, fundamental and anti-Stokes waves collinear. By adjusting the angle of KTP, the anti-Stokes radiation can be tuned in the range of 1009 to 1021 nm. The effective Raman gain coefficient was estimated to be 2.1 cm/GW.8. The KTP IOPO pumped by a Kerr-lens mode-locked laser coupled with an acousto-optic modulator was first demonstrated in this dissertation. In this section, different gain media was employed such as Nd:GGG and composite Nd:YVO4 crystals so that high peak power and high energy subnanosecond signal beams could be obtained. The maximum peak power was 102 kW from KLM Nd:GGG laser pumped KTP IOPO, and the minimum pulse duration was 120 ps from KLM YVO4/Nd:YVO4 laser pumped KTP IOPO. Considering the loss induced by the Kerr effect, coupled rate equations were modified and the numerical solutions were in agreement with the experimental results.9. A KTP IOPO pumped by a dual-loss-modulated QML Nd:GGG laser with acousto-optic modulator and Cr4+:YAG was first realized in this dissertation. A V-type resonator was adopted in order to simplify the configuration. Under an incident LD pump power of 8.25 W, the maximum pulse energy was 96 μJ with a Q-switched envelope duration of 2.5 ns at an AOM modulation rate of 1 kHz. The maximum output power of signal beam was 156 mW with an AOM modulation rate of 5 kHz, which is the highest output power from a QML laser pumped IOPO.10. A single mode-locking laser pumped KTP OPO was realized with AOM and Cr4+:YAG as dual-loss modulator. Under an incident LD pump power of 10.5 W and an AOM modulation rate of 2 kHz, the minimum pulse duration for the signal beam was 450 ps with a highest peak power of 35.5 kW. In this section, the signal wavelength variation as a function of the KTP temperature was also investigated and we found that the blueshift ratio with the temperature was 0.027 nm/℃. Given the fluctuations of the QML laser, a set of coupled rate equations for QML laser pumped IOPO was built up. The numerical solutions were in agreement with the experimental results.The main innovations in this dissertation are listed as following:1. First demonstration of simultaneous SRS and OPO processes in a single KTP crystal. The beam quality factor was measured as 1.2.2. First demonstration of dual-loss-modulated Q-switched laser pumped IOPO and SRS, in which the signal pulse duration was compressed to 580 ps.3. First modelling of a Q-switched dual-wavelength laser pumped OPO and SRS in a single crystal. The numerical solutions accorded well with the experimental results.4. First realization of KLM laser pumped OPO, resulting in a high peak power, high energy and subnanosecond signal beam.5. First report on the dual-loss-modulated QML laser pumped OPO, leading to a stable subnanosecond signal wave with high peak power and high energy.6. First realization of single mode-locked laser pumped OPO, giving a minimum pulse duration of the signal beam of 450 ps. According to the fluctuation mechanism of QML laser, the first model about the OPO pumped by QML laser was reported.7. First realization of Yb:YAG/KTP third Stokes laser at 1150 nm, corresponding to a minimum pulse duration of 764 ps. The effective Raman gain coefficient of KTP was first estimated to be 2.1 cm/GW.8. First output power above 1 W from a Nd,MgO:LiNbO3 laser. As an application, this laser pumped KTP OPO with a signal wavelength at 1630 nm was obtained.
Keywords/Search Tags:Optical Parametric Oscillator (OPO), Stimulated Raman Scattering (SRS), subnanosecond pulses, dual-loss modulation, Q-switching, Q-switching and mode-locking, Nd,MgO:LiTaO3 crystal, Nd,MgO:LiNbO3 crystal, monolayer graphene, KTP crystal
PDF Full Text Request
Related items