We report on the continuous-wave (CW) and, for what we believe to be the first time, passively mode-locked (ML) laser operation of an Yb3+-doped YSr3(PO4)3 crystal. Utilizing a 976-nm spatially single-mode, fiber-coupled laser diode as pump source, the Yb:YSr3(PO4)3 laser delivers a maximum CW output power of 333â mW at 1045.8â nm with an optical efficiency of 55.7% and a slope efficiency of 60.9%. Employing a quartz-based Lyot filter, an impressive wavelength tuning range of 97â nm at the zero level was achieved in the CW regime, spanning from 1007â nm to 1104â nm. In the ML regime, incorporating a commercially available semiconductor saturable absorber mirror (SESAM) to initiate and maintain soliton-like pulse shaping, the Yb:YSr3(PO4)3 laser generated pulses as short as 61 fs at 1062.7â nm, with an average output power of 38â mW at a repetition rate of â¼66.7â MHz.
We derive the parametric equations for the geometric rays of a periodic orbit inside a confocal cavity. Based on the derived formula, we demonstrate a passively mode-locked solid-state laser with a low pulse repetition rate to obtain a pulse train traveling along zigzag multi-pass trajectories. We achieve a stable mode-locked pulse train with a pulse repetition rate of 18â MHz by designing the cavity to satisfy the dual-M trajectory. Furthermore, by precisely adjusting cavity mirrors under the same experimental setup, we can reach pulse repetition rates of 12 and 9â MHz for the mode-locked laser. It is believed that the numerical calculation and the developed experiment can provide a straightforward and convenient way to achieve a low pulse repetition rate for passively mode-locked lasers.
Two compact laser sources at 707 and 714â nm are realized efficiently by using a diode-pumped a-cut Nd:YVO4 laser with intracavity stimulated Raman scattering and sum-frequency generation (SFG). The fundamental wave at 1342â nm is generated by the 4F3/2 â 4I13/2 transition in Nd:YVO4 crystal. The Raman Stokes waves at 1496 and 1526â nm were obtained by placing the c-axis of the Nd:YVO4 crystal along the Ng and Nm axes of an Np-cut KGW crystal, respectively. LBO crystals with critical phase matching are used to perform the intracavity SFG of fundamental and Stokes waves. At a pump power of 36 W, the maximum output powers at 707 and 714â nm can reach 2.72 and 3.14 W, corresponding to light-to-light conversion efficiencies of 7.5% and 8.7%, respectively. The developed 707 and 714â nm laser sources are practically useful in laser trapping and cooling related to atomic strontium and radium.
A low-threshold continuous wave dual-wavelength mid-infrared laser is demonstrated by using an intracavity optical parametric oscillator (OPO) with a dual-wavelength pump wave. To realize a high-quality dual-wavelength pump wave, a composite Nd:YVO4/Nd:GdVO4 gain medium is applied for a linear polarized state and synchronization output. With the quasi-phase-matching OPO process, it is found that the dual-wavelength pump wave shares equal signal wave oscillation and leads to a lower OPO threshold. Finally, a diode threshold pumped power of barely 2 W can be achieved for the balanced intensity dual-wavelength watt-level mid-IR laser.
Efficient diode-pumped passively Q-switched Nd:YVO4 yellow and orange lasers are developed with the pulse pumping scheme and the intracavity stimulated Raman scattering (SRS) and second harmonic generation (SHG). A Np-cut KGW is exploited in the SRS process to generate the yellow 579 nm laser or the orange 589 nm laser in a selectable way. The high efficiency is achieved by designing a compact resonator to include a coupled cavity for intracavity SRS and SHG and to provide a focused beam waist on the saturable absorber for reaching an excellent passive Q-switching. The output pulse energy and peak power can reach 0.08 mJ and 50 kW for the orange laser at 589 nm. On the other hand, the output pulse energy and peak power can be up to 0.10 mJ and 80 kW for the yellow laser at 579 nm.
A compact efficient continuous wave (CW) laser with selectable two wavelengths at 671 and 714â nm is developed. The laser cavity comprises an Nd-doped and an undoped YVO4 crystal to generate the fundamental wave at 1342â nm and the first-Stokes Raman wave at 1525â nm, respectively. A single LBO crystal with the cut angle in the XZ plane is designed to achieve the selectable phase-matching via the thermal tuning for the second harmonic generation (SHG) of 1342â nm and the sum frequency generation (SFG) of 1342 and 1525â nm. At a pump power of 40 W, the optimal output powers at 671 and 714â nm can reach 4.5 and 1.8 W, respectively. The present compact CW laser source at 671 and 714â nm has practical usefulness for laser spectroscopy and numerous applications.
The anisotropic thermal lens effect of a dual-polarization Nd:YLF laser is experimentally investigated by measuring the transverse beat frequency between TEM0,0 and TEM1,0 modes in the self-pulsing operation, and focal lengths of thermal lensing for both polarizations can be accurately determined. The focal length of the thermal lens for π polarization was observed to be negative and varies from -1.1 to -0.5m for the absorbed pump power increasing from 1.7 to 3.8 W. For σ polarization, the focal length of the thermal lens was determined to be positive and varies from 1.2 to 0.9 m for the absorbed pump power increasing from 8.4 to 10.9 W. The sensitivity factors of the thermal lens for both polarizations were evaluated to be Mπ=-0.54m-1/W and Mσ=0.1m-1/W, respectively.
We propose a theoretical model to generate the resonant geometric modes localized on ray periodic trajectories with orbital angular momentum. Based on the numerical analysis, we realize resonant geometric modes in the off-axis pumped degenerate cavity ${\rm Nd}{:}{{\rm YVO}_4}$Nd:YVO4 lasers with an external mode converter. The experimental results reveal that laser output modes display the planar geometric modes when the off-axis displacement is sufficiently large, and the cavity length is set to satisfy the degenerate conditions. To generate the vortex beams, the planar geometric modes are transformed into circular geometric modes. Finally, the resonant geometric modes with large orbital angular momentum (OAM) can be generated from converting the circular geometric modes with an axicon lens. The experimental results are performed to approve the theoretical analyses.
A novel scheme to realize a mode-locked laser with a narrow spectral linewidth is demonstrated by exploiting a reflected Fabry-Perot (FP) cavity to introduce an intense FP effect. Stable continuous-wave mode-locked operation is achieved with the repetition rate of 48 MHz and the maximum average output power of 2.6 W under an incident pump power of 11.9 W. The mode-locked pulse width is systematically investigated by varying the optical thickness of the reflected FP cavity. The pulse duration is experimentally found to be in a range of 0.8 to 2.6 ns. The experimental results reveal that the reflected FP cavity is the key factor leading to the pulse generation in the nanosecond regime. This Letter is believed to provide a promising method for generating optical pulses with narrow spectral linewidths.
A continuous-wave (cw) self-mode-locked Tm:YAG laser at 2015 nm is successfully demonstrated by suppressing the self-pulsing behavior. By using rate equations to simulate the laser temporal dynamic, the theoretical analysis indicates that the reabsorption-induced self-pulsing for the Tm:YAG laser can be suppressed with sufficient pump power. It is experimentally confirmed that at absorbed powers higher than 6 W, the self-pulsing can be eliminated and a cw self-mode-locked pulse is generated instead of the Q-switched mode locking. At an absorbed power of 6.8 W, the output power of the self-mode-locked Tm:YAG laser reaches 1.22 W with corresponding pulse duration of 3 ps and a repetition rate of 3.376 GHz.
A synchronously dual self-mode-locked (SML) operation at 946 and 1064 nm is experimentally accomplished by using a compact coupling scheme to obtain the optical beating frequency up to 35.2 THz. The SML emissions at 946 and 1064 nm are established by a monolithic Nd:YAG cavity and a Nd:YVO4 crystal in a flat-flat cavity, respectively. Two gain media are butt adjoined to be longitudinally pumped by a single laser diode. The monolithic Nd:YAG crystal is used not only as the 946 nm laser cavity, but also as the output coupler of the Nd:YVO4 1064 nm laser. More importantly, the output surface of the monolithic Nd:YAG laser is coated to generate the optical feedback for the synchronization of the dual SML operation. At a pump power of 10.7 W, the output powers at 1064 and 946 nm can simultaneously reach 1.5 W by controlling the focal position of the pump waist.
We experimentally observe an intriguing phenomenon of complex spatio-temporal dynamics in a commercial optically pumped semiconductor laser with intracavity second harmonic generation. We numerically verify that the experimental results come from the total mode locking of transverse electromagnetic modes (TEM00) and higher-order modes with significant astigmatism. The scenarios of the spatio-temporal dynamics are quite similar to the phenomena in soft-aperture Kerr-lens mode locked Ti:sapphire lasers.
