Stable Single-frequency Laser Research Articles

Speckle-displacement-based wavemeter for mode-hop and side-mode detection.

A speckle-displacement-based wavemeter is combined with a spatial-fundamental-mode-pass filter to eliminate the influence of multimode operation on the directionality of the resulting output from a distributed Bragg reflector (DBR) tapered laser. The proposed setup is characterized theoretically and experimentally, and detections of mode hops and side-mode suppression ratios (SMSRs) in the optical output are demonstrated. The laser illuminates a rough surface at an oblique angle, and a camera observes the corresponding speckle pattern from an almost identical back-scattering direction. As the wavelength of the laser shifts, the speckle pattern responds with a corresponding displacement, which is approximately linear with respect to the shift within the detection area. The wavemeter tracks continuously the shifts of the speckles pattern by tracking the peak of the covariance function of sequentially acquired images. In this way, the speckle-displacement-based wavemeter achieves a spectral resolution of 10.4 MHz. Mode hops in the laser do not cause any impeding decorrelation of the speckle patterns. Interestingly, the actual SMSR is related to the peak height and width of the absolute covariance function. A wavemeter, which is capable of measuring wavelengths, mode hops, and SMSRs, is highly useful for spectroscopy, quantum optics, nonlinear frequency conversion, and other applications requiring stable single-frequency laser light, especially when using diode lasers.

110 mW single-frequency Yb:YAG crystal-derived silica fiber laser at 1064 nm.

A single-frequency laser based on Yb:YAG crystal-derived silica fiber (YDSF) was demonstrated. The YDSF was fabricated by a molten-core method with a doping concentration of 4.8wt. % for Yb2O3, whose gain coefficient and transmission loss were measured to be 1.7dB/cm and 0.005dB/cm, respectively. An over 110mW stable single-frequency laser at 1064nm was obtained based on a distributed Bragg reflector setup, showing a slope efficiency of 18.5%. The signal-to-noise ratio was ∼80 dB, and the frequency fluctuation was less than 20MHz within 10min.

Stable high-power Er:YAG ceramic single-frequency laser at 1645 nm.

A stable high-power single-frequency laser at 1645 nm from a monolithic Er:YAG ceramic nonplanar ring oscillator (NPRO) was demonstrated. 10.7 W single-frequency laser output was obtained with a slope efficiency of 61.2% and an optical efficiency of 52.1% with respect to incident pump power. The laser always stably operated in single-frequency mode with the pump power increasing from threshold to maximum pump power. When the crystal's set temperature changed from 17.2°C to 26.6°C, the Er:YAG ceramic NPRO had stable single-frequency laser output, and the widest continuous tuning range without mode-hoping was 4.5 GHz. The linewidth of the single-frequency laser was 5.75 kHz. The beam quality M2 factors were 1.23 and 1.24 in x and y directions, respectively.

Short all Tm-doped germanate glass fiber MOPA single-frequency laser at 1.95 μm.

Based on heavily Tm-doped germanate glass fibers (TGFs), a short all-TGF MOPA laser system with uniform core parameters in each stage was demonstrated. An 11.7 W stable single-frequency laser at 1.95 μm with an optical-to-optical conversion efficiency of 20.4% is obtained from a homemade 31-cm-long double-cladding single-mode TGF. The estimated stimulated Brillouin scattering (SBS) threshold of 980 W and the measured relative intensity noise of < -130 dB/Hz for frequencies above 2 MHz are achieved in this MOPA system. Furthermore, the prospect for further power-scaling of such short MOPA laser is considered.

Suppressing the preferential σ-polarization oscillation in a high power Nd:YVO4 laser with wedge laser crystal

We observe the phenomenon of priority oscillation of the unexpected σ-polarization in high-power Nd:YVO4 ring laser. The severe thermal lens of the σ-polarized lasing, compared with the π-polarized lasing, is the only reason for the phenomenon. By designing a wedge Nd:YVO4 crystal as the gain medium, the unexpected σ-polarization is completely suppressed in the entire range of pump powers, and the polarization stability of the expected π-polarized output is enhanced. With the output power increasing from threshold to the maximum power, no σ-polarization lasing is observed. As a result, 25.3 W of stable single-frequency laser output at 532 nm is experimentally demonstrated.

Resonantly pumped monolithic nonplanar Ho:YAG ring laser with high-power single-frequency laser output at 2122 nm

We demonstrated a stable single-frequency laser operating at 2122 nm from a monolithic nonplanar Ho:YAG ring oscillator (NPRO). The Ho:YAG NPRO was resonantly pumped by a 1907 nm Tm:YLF laser built up by ourselves. The maximum multimode output power from the Ho:YAG NPRO was 9.66 W and the slope efficiency was 71.7%. With accurate adjustment of the pump position to make the laser oscillate in single frequency condition, an output power of 8.0 W was obtained with a slope efficiency of 61.4% and an optical-optical efficiency of 50.0%. The power stability of the Ho:YAG NPRO laser was 0.29% at maximum single frequency output power. The beam quality M(2) factors were measured to be less than 1.1 in x- and y- directions.