Frequency-modulated Nd:YAG microchip lasers

Solution-processed whispering-gallery-mode microsphere lasers based on colloidal CsPbBr3perovskite nanocrystals

Perovskite nanocrystals (NCs) have emerged as attractive gain materials for solution-processed microlasers. Despite the recent surge of reports in this field, it is still challenging to develop low-cost perovskite NC-based microlasers with high performance. Herein, we demonstrate low-threshold, spectrally tunable lasing from ensembles of CsPbBr₃NCs deposited on silica microspheres. Multiple whispering-gallery-mode lasing is achieved from individual NC/microspheres with a low threshold of ∼3.1μJ cm^-2and cavity quality factor of ∼1193. Through time-resolved photoluminescence measurements, electron-hole plasma recombination is elucidated as the lasing mechanism. By tuning the microsphere diameter, the desirable single-mode lasing is successfully achieved. Remarkably, the CsPbBr₃NCs display durable room-temperature lasing under ∼10⁷shots of pulsed laser excitation, substantially exceeding the stability of conventional colloidal NCs. These CsPbBr₃NC-based microlasers can be potentially useful in photonic applications.

Low-threshold upconverted single-mode lasing from CdS hexagonal microcavities

Upconversion micro/nanolasers are promising in fundamental physics research and practical applications. However, due to the limitation of gain medium and cavity quality, such lasers still suffer from a high lasing threshold (P _th). Herein, upconverted whispering-gallery-mode lasing by two-photon absorption is achieved from CdS microplatelets with single-mode emission and low threshold (∼1.2 mJ cm^-2). The threshold is three times lower than the best reported value in previous CdS upconversion lasers. Moreover, wavelength-tunable upconverted single-mode lasing is demonstrated from 510.4 to 518.9 nm with narrow linewidths around 0.85 nm, which is further verified through numerical simulations. In addition, the size-dependent lasing behavior is realized from single-mode to multimode oscillation; the corresponding lasing threshold decreases with increasing cavity edge length (L), following a P _th ∝ 1/L ² relationship. These results underscore the promise of CdS microplatelets for developing chip-level frequency upconversion lasers.

14 GHz broadband and continuously frequency-tuned Nd:YVO4 laser with an RTP etalon

A laser-diode-pumped broadband and continuously frequency-tuned all-solid-state Nd:YVO₄ laser at 1064 nm with an output power of 200 mW is demonstrated. A RbTiOPO₄ (RTP) etalon and a piezoelectric-transducer (PZT) are utilized for coarse and fine frequency tuning, respectively. Dependence of the frequency excursion on the applied voltage to the RTP etalon and the displacement of the PZT is theoretically and experimentally investigated. A continuous frequency tuning of 14 GHz is conducted by synchronous adjustment of the RTP etalon and the PZT. The tuning covers more than 6 times the longitudinal mode spacing of a laser resonator without any mode hops.

Linearly frequency-tuned LD-pumped Nd:YVO4 laser with an 18-GHz broadband tuning range

A continuously frequency-tuned laser diode end-pumped Nd:YVO₄ laser at 1064 nm is demonstrated. A coated etalon and a piezoelectric-transducer (PZT) are utilized for coarse and fine frequency tuning, respectively. Broadband and linear frequency tuning without mode hops is conducted by the synchronous adjustment of the etalon and the PZT. Dependence of the frequency excursion on the displacement of the PZT and the tilting angle of the etalon are theoretically and experimentally investigated. A linear frequency tuning range up to 18 GHz without mode hops or frequency overlaps in a one-way non-stopped scanning is obtained. The maximum output power is 930 mW at 1064 nm, and the average frequency tuning speed is 1.24 GHz/s. Standard deviation of the frequency variation to a linear frequency tuning is estimated to be 186 MHz, indicating a high tuning linearity.

Laser diode side-pumped Nd:YVO4 microchip laser with film-etched microcavity mirrors

Microchip lasers are applied as the light sources on various occasions with the end-pumping scheme. However, the vibration, the temperature drift, or the mechanical deformation of the pumping light in laser diodes in the end-pumping scheme will lead to instability in the microchip laser output, which causes errors and malfunctioning in the optic systems. In this paper, the side-pumping scheme is applied for improving the disturbance-resisting ability of the microchip laser. The transverse mode and the frequency purity of the laser output are tested. To ensure unicity in the frequency of the laser output, numerical simulations based on Fresnel-Kirchhoff diffraction theory are conducted on the parameters of the microchip laser cavity. Film-etching technique is applied to restrain the area of the film and form the microcavity mirrors. The laser output with microcavity mirrors is ensured to be in single frequency and with good beam quality, which is significant in the applications of microchip lasers as the light sources in optical systems.

Exploring transverse pattern formation in a dual-polarization self-mode-locked monolithic Yb: KGW laser and generating a 25-GHz sub-picosecond vortex beam via gain competition

Formation of transverse modes in a dual-polarization self-mode-locked monolithic Yb: KGW laser under high-power pumping is thoroughly explored. It is experimentally observed that the polarization-resolved transverse patterns are considerably affected by the pump location in the transverse plane of the gain medium. In contrast, the longitudinal self-mode-locking is nearly undisturbed by the pump position, even under the high-power pumping. Under central pumping, a vortex beam of the Laguerre-Gaussian LGp,l mode with p = 1 and l = 1 can be efficiently generated through the process of the gain competition with a sub-picosecond pulse train at 25.3 GHz and the output power can be up to 1.45 W at a pump power of 10.0 W. Under off-center pumping, the symmetry breaking causes the transverse patterns to be dominated by the high-order Hermite-Gaussian modes. Numerical analyses are further performed to manifest the symmetry breaking induced by the off-center pumping.

Single-Mode Operation and Frequency Doubling of Fiber-Coupled Diode Butt-Coupling-Pumped Nd:YVO(4) Lasers

We present a simple way to achieve single-frequency operation by using a fiber-coupled diode butt-coupling-pumped Nd:YVO(4) laser in a flat-flat cavity. Single-mode outputs of 620 and 260 mW for fundamental and second-harmonic wavelengths were obtained when the laser was pumped by an 1100-mW fiber-coupled laser diode. Experimental results show that thermal effects provide not only a stable resonator with a good overlap of laser mode and pump size but also enhance single-frequency performance.

Tm:YVO(4) microchip laser

When pumped with a 1-W laser diode, a Tm:YVO(4) microchip laser produced 150 mW of 1.92-µm output in a near-diffraction-limited beam at room temperature. Using a Ti:Al(2)O(3) laser to pump the same device, we showed that reducing the temperature of the Tm:YVO(4) from 20 to -30 °C resulted in no measurable change in threshold and increased the slope efficiency by only 20%.

Single-mode 1.34-microm Nd:YVO(4) microchip laser with cw Ti:sapphire and diode-laser pumping

We report cw single-mode output at 1.34 microm in a Nd:YVO(4) microchip laser pumped separately with a Ti:sapphire laser and a diode laser in the region of 809 nm. The 0.5 mm x 1.0 mm x 1.0 mm Nd(3+)-doped YVO(4) crystal produced output powers as high as 60 mW with slope efficiencies as high as 40% and laser thresholds between 155 and 275 mW by use of a pumped volume of approximately 150-microm diameter and 0.5-mm length. Data are also presented for the laser's performance as a function of pump wavelength and for the spectral variation of the output with crystal temperature.

Dual-polarization modes and self-heterodyne noise in a single-frequency 2.1-microm microchip Ho,Tm:YAG laser

We have observed, for the first time to our knowledge, residual stress-induced birefringent dual-polarization modes in a diode-pumped, single-frequency, microchip cw 2.0914-microm Ho,Tm:YAG laser. The two orthogonally polarized modes were separated in frequency by approximately 12 MHz and, when photodetected, produced a 12-MHz self-heterodyne beat signal. The self-heterodyne signal could be eliminated by an external lambda/4 plate and a polarizer to filter out one of the modes, but this required regulation of the pump laser power to better than 1%. These results have important implications for use of the microchip Ho,Tm:YAG laser in a heterodyne detection coherent lidar.

Diode-pumped microchip Er-Yb:glass laser

A single-frequency, diode-pumped, Er-Yb:glass microchip laser at a 1530-nm wavelength has been designed and operated. An output power of greater than 25 mW, a linewidth narrower than 1 kHz, and a slope efficiency of 22% have been obtained.

Phase locking of 1.32-microm microchip lasers through the use of pump-diode modulation

Two diode-pumped 1.32-microm Nd:YAG microchip lasers have been phase locked through the use of current modulation of the pump diode to control the frequency of the slave device. The frequency response of the microchip laser to pump-diode modulation is discussed, and the feedback circuit is described.

Single-mode oscillation of laser-diode-pumped Nd:YVO(4) microchip lasers

Single-mode-oscillation output power of ~103 mW has been observed in 1.1-at.%-doped Nd:YVO(4) pumped with a 500-mW laser diode. Continuous-wave thresholds of ~5.3 mW have been observed with slope efficiencies of greater than 32.4%. The microchip laser can be tuned over 107 GHz, without mode hopping, by heating the laser crystal.