Optical-optical Conversion Efficiency Research Articles

Single- and dual-tube He-Ne lasers for high-power excitation of LG01-mode vortex beam

Abstract In this study, aiming to extend the power of LG01-mode vortex light at 632.8nm, the commercial He-Ne laser was upgraded to dual-tube gain geometry with the assistance of an intracavity spot defect for spatial filtering. We investigated the impact of using single and double He-Ne gas gain tubes on the powers of vortex laser output , and achieved a maximum 4.7-mW power of LG01-mode vortex light, correspionding to an optical-optical conversion efficiency of 39.2% and making it the highest power of vortex light obtained in He-Ne laser.

Enhanced laser performance in an LD end-pumped YAP/Tm:YAP/YAP bonding rod with concave end faces.

We demonstrate the effects of thermal bonding and concave end faces on the laser performance of 795 nm LD end-pumped Tm:YAP crystals for the first time. Analysis of the thermal focal length shows that the thermal lensing effect can be effectively compensated by the concave end faces. By combining the thermal bonding with the concave end faces, a maximum output power of 42.5 W is achieved on the concave YAP/Tm:YAP/YAP bonding rod with a negative curvature radius of 500 mm, corresponding to a slope efficiency of 47.4% and an optical-optical (O-O) conversion efficiency of 41.6%. Moreover, the beam quality factors Mx2/My2 are fitted to 1.67/1.69. Compared with the flat YAP/Tm:YAP/YAP bonding rod, the concave YAP/Tm:YAP/YAP bonding rod significantly increases the maximum output power from 36.56 W to 42.5 W, with an approximately 4% improvement in both the slope efficiency and O-O conversion efficiency. These results indicate that the combination of thermal bonding and concave end faces can effectively improve the heat dissipation capacity and mitigate the thermal lensing effect, thereby yielding near-infrared (NIR) laser output with high performance.

High repetition rate step acousto-optic Q-switched laser with three nanosecond equal-interval and amplitude pulses

A compact, high repetition rate pulse group laser with three nanosecond equal-interval and equal-amplitude sub-pulses has been demonstrated in this paper. Under three-step nanosecond continuous acousto-optic control, a laser pulse group containing three nanosecond interval sub-pulses can be realized. The three sub-pulses have a pulse width of 15 ns, 23 ns, and 25 ns and minimum pulse intervals of 119 ns at a repetition rate of 30 kHz. The corresponding optical-optical conversion efficiency is 29.2 %.

Intra-Cavity Cascaded Pumped 946/1030 nm Dual-Wavelength Vortex Laser Using a Spot-Defect Mirror

Due to their unique properties, vortex lasers have high application value in frontier fields such as optical micromanipulation, super-resolution imaging, quantum entanglement, and optical communication. In this study, we demonstrated a 946/1030 nm Laguerre-Gaussian (LG01) mode dual-wavelength vortex laser by using an intracavity cascade pumped structure and a spot-defect output mirror. Using a coaxial linear cavity structure, the 808 nm laser diode (LD) was used to end-pump the Nd:YAG crystal to generate a 946 nm laser and then use it to directly pump the Yb:YAG crystal in the cavity to generate a 1030 nm laser, and finally a 946/1030 nm dual-wavelength laser came out. By making a spot defect in the center of the output mirror to suppress the oscillation of the fundamental Gaussian mode laser and carefully adjusting the position of the laser crystals, the LG01 mode dual-wavelength vortex laser was output in single handedness. When the pump power was 40 W, the total output was 664 mW (356 and 308 mW at 946 and 1030 nm LG01 mode vortex lasers), and the total optical-optical conversion efficiency was 1.7%; the output power fluctuations of 946 and 1030 nm LG01 mode vortex lasers within 1 h were 3.43% and 3.13%, respectively; the beam quality factors M2 of 946 and 1030 nm LG01 mode vortex lasers were 2.35 and 2.40, respectively. It was proved that the generated dual-wavelength vortex laser had the wavefront phase expiϕ by the self-interference method.

946/1030 nm Dual-Wavelength Laguerre-Gaussian (LG01) Mode Vortex Laser Based on Intracavity Cascade Pumped Resonator

In this paper, the 946/1030 nm dual-wavelength LG01 mode vortex laser is obtained by applying the intracavity cascade pumped structure and annular-beam end-pumped method, an innovative and pioneering exploration of the transverse mode of the dual-wavelength laser. First, we demonstrate the oscillation characteristic theoretical model of the dual-wavelength LG01 mode laser, considering the reabsorption effect. Then the length of the laser crystal and the transmittance of the output mirror are simulated and analyzed, respectively, related to the oscillation characteristics of the 946 and 1030 nm LG01 mode vortex lasers. Finally, a 946/1030 nm LG01 mode vortex laser with the same handedness is successfully achieved in our experiment. With 20 W of annular-beam pump power, the output power of 946 and 1030 nm LG01 mode vortex lasers is 0.404 and 0.510 W, the slope efficiency is 3.6% and 6.2%, and the total optical-optical conversion efficiency is 4.6%. At the maximum output power, the fluctuations of output power within 1 h are 4.02% and 4.23%, and the beam quality factors M2 are 2.32 and 2.27, respectively, for 946 and 1030 nm LG01 mode vortex lasers. The wavefront phase exp(iϕ) of the 946/1030 nm dual-wavelength is also proved by the self-interference method.

Ce,Tb,Gd:YAG-Al2O3 eutectic crystal phosphor plates for high-power warm white LED applications

Ce,Tb,Gd:YAG-Al2O3 eutectic crystal phosphor plates (ECPPs) were grown by the micro-pulling-down (μ-PD) method to adjust correlated color temperature (CCT) and color rendering index (Ra) for high-power warm white LED applications. Tb3+ and Gd3+ ions in Ce:YAG-Al2O3 play a positive role in spectra adjustment based on the structural and luminescent properties investigations. Tb3+ ions enhance the fluorescence lifetime of Ce3+ ions from 61.1 to 63.8 ns and improve the luminescence efficiency, and the highest optical-optical conversion efficiency (OCE) is 270.56 lm/W. Corresponding luminescence shift from cold white to greenish yellow. Gd3+ ions increase the peak wavelength from 554 to 564 nm and improve the Ra value, and the maximum Ra is 75.5. Corresponding luminescence is shifted from cold white to reddish violet. In addition, the luminescence of Ce,Tb,Gd:YAG-Al2O3 ECPPs is adjusted to warm white with CIE coordinate (0.374, 0.364) and CCT of 4102 K, and Ra of 73.0, which is of great significance for realizing the high-power warm white LED lighting.

Optical parametric oscillator with adjustable pulse width based on KTiOAsO4

A type II non-critically phase-matched KTiOAsO4 (KTA) optical parametric oscillator (OPO) was pumped by a 1064 nm laser with an adjustable output pulse width. This enabled the generation of signal and idler outputs with variable pulse width. When the pulse width of the 1064 nm pump field was varied in the range 5.7–12.6 ns, the corresponding pulse widths of the 1538 nm (signal) and 3468 nm (idler) fields varied in the ranges 5.7–7.9 ns and 7.1–19.7 ns respectively. Under a pulse repetition rate of 20 Hz, maximum output pulse energies of 0.44 mJ at 3468 nm and 1.135 mJ at 1538 nm were obtained for a pump energy of 8.8 mJ. The maximum optical-optical conversion efficiency (pump to combined signal and idler) of this system was 17.9%, and the maximum slope efficiency was 50.7%.

Research on 946 nm LG01 mode laser considering thermal effect

Laguerre–Gaussian (LG) beams have important application prospects in Frontier Fields such as optical micromanipulation, optical communication, and super-resolution microscopy. In this letter, the thermal effect generated by Nd:YAG crystal that is end-pumped by the annular-beam is taken into account in the analysis of the LG01 mode beam generation. The 946 nm LG01 mode laser is obtained by using annular-beam end-pumped Nd:YAG crystal shaped by custom mirror M01. When the incident pump power is 19.9 W, the maximum output power is 1.35 W, the optical-optical conversion efficiency is 6.8%, the slope efficiency is 10.9%, and the beam quality factor M2 in X and Y directions is 2.22 and 2.28 respectively. The handedness of LG01 mode laser remains stable in the whole pump range. The theoretical model established considering thermal effects can guide the design of LG mode lasers, and the 946 nm LG01 mode laser obtained expands the new wavelength of vortex light and increases its potential new application direction.

Passively Q-Switched Dual-Wavelength Laser Operation With Coaxially End-Pumped Composite Laser Materials

A passively Q-switched dual-wavelength laser with tunable power ratio and pulse interval is demonstrated based on the coaxial diode end-pumping configuration by varying the pump wavelength. A theoretical model was built by a set of time-domain rate equations illustrating the dynamic process of both the pulse generation of two wavelengths from a shared pump source and a saturable absorber. The simulation showed that both the power ratio and the time interval between the pulses at two resonant wavelengths in the Q-switched mode could be tuned by balancing the gains in two laser crystals by varying the pump wavelength, realized by controlling the working temperature of the pump laser diode. The experiment was performed with Nd:YAG/Nd:YAP composite laser crystals and a Cr4+:YAG slice working as the saturable absorber for pulse generation. The continuous-wave and Q-switched total output power reached 5.62 W and 2.12 W, corresponding to overall optical-optical conversion efficiencies of 37.5% and 14.1%, respectively. The manipulation of power ratio and pulse interval between 1064 nm and 1080 nm agreed well with the simulation results.

Highly efficient actively Q-switched Nd:YAG laser

A novel gain medium structure is designed providing Q-switched pulses with high efficiency. The use of an improved corner-side hybrid pump structure achieves a high absorption efficiency of pump light by crossing through the active media 13 times Nd:YAG. A layer of Sm:YAG is bonded around the active media, which suppresses parasitic oscillation and amplified spontaneous emission (ASE) effectively. A high-efficient actively Q-switched laser is successfully realized with a pulse energy of 104 mJ. The corresponding optical-optical conversion efficiency is 30.5%. This is, to the best of our knowledge, the highest optical to optical efficiency for an actively Q-switched Nd:YAG laser at the hundred milli-joules level.

Novel Highly Efficient In-Band Pump Wavelengths for Medium Slope Efficiency Holmium-Doped Fiber Amplifiers

We report the design and performance of medium slope efficiency (64%) Holmium-doped fiber amplifiers (HDFAs) with novel alternative in-band pump wavelengths in the 1720-2000 nm spectral region. We demonstrate through simulations that pump wavelengths of 1840-1860 nm can yield significantly improved output power, gain, and optical-optical conversion efficiency compared to the previous technical and industry standard pump wavelength of 1940 nm. Our simulations are verified by experimental data.

High-Efficiency Ho:YAP Pulse Laser Pumped at 1989 nm

A Tm:YAP laser with an output wavelength of 1989 nm was selected for the first time as the pump source of a Q-switched Ho:YAP laser. When the absorbed power was 30 W, an average power of 18.02 W with the pulse width of 104.2 ns acousto-optic (AO) Q-switched Ho:YAP laser was obtained at a repetition frequency of 10 kHz. The slope efficiency was 70.11%, and the optical-optical conversion efficiency was 43.03%. The output center wavelength was 2129.22 nm with the line width of 0.74 nm.

Enhancing Q-Switched Fiber Laser Performance Based on Reverse Saturable and Saturable Absorption Properties of CuCrO2 Nanoparticle-Polyimide Films

We demonstrate CuCrO2 (CCO) nanoparticle (NP)-polyimide (PI) composite film as a saturable absorber (SA) to regulate the output characteristics of passively Q-switched fiber laser at 1.55 μm. Based on the reverse saturable and saturable absorptions of the CCO NP-PI film, the passively Q-switched fiber laser expressed two stages with the increase of pump power for substantial performance enhancement. Reverse saturation absorption is observed to introduce appropriate cavity loss, which constructs effective pathways for promoting both the modulation depth and over threshold degree, as well as reducing the photon lifetime. In particular, our results realized the pulse duration and repetition rate compressing simultaneously for the first time. The second stage output laser exhibits a peak power of 1016 mW and a single pulse energy of 183 nJ, which are about 88 and 9 times higher than those of the first stage. Furthermore, the optical-optical conversion efficiency is up to 1270%. All of these can evidently demonstrate the importance of the appropriate cavity loss design for optimizing the Q-switched pulse laser output characteristics.

Optical and laser performances of a layered ReSe2 saturable absorber for a 2-µm solid laser

In this paper, a dispersion solution of rhenium diselenide (ReSe2) was prepared using an ultrasonic decomposition method and prepared for use as a saturable absorber (SA) mirror by spin-coating. The optical characteristics of the ReSe2 SA were characterized to acquire those parameters which were saturated at 2 μm. A passively mode-locked (PML) Tm:YAG laser with an ReSe2 SA was first demonstrated in an experiment. Under a continuous wave (CW) regime, a 1940-mW output power was achieved at 2013.8 nm with a pump power of 22.4 W. In PML mode, a 320-mW average output power and a 580.5-ps pulse duration at 203.1 MHz were acquired from the PML Tm:YAG laser with an output wavelength of 2012.6 nm, corresponding to a pulse energy of 1.58 nJ and an optical-optical conversion efficiency of 2.2%.

Room temperature watt-level 3.87 µm MgO:PPLN optical parametric oscillator under pumping with a Tm:YAP laser.

A room-temperature highly efficient Tm:YAP laser pumped MgO:PPLN optical parametric oscillator operating at 3.87 µm near degeneracy is demonstrated. The pump source is an acousto-optical (AO) Q-switched Tm:YAP laser, which delivers a maximum output power of 6.17 W with a pulse duration of 45 ns and a repetition rate of 6 kHz. The temperature dependent wavelength tuning characteristics of the PPLN-OPO is investigated, and a maximum OPO output power of 1.2 W at around 3.87 µm is achieved at 35°C, corresponding to an optical-optical conversion efficiency of 19.4%. To the best of our knowledge, this is the maximum output power ever reported from 2 µm waveband laser pumped 3-5 µm MgO:PPLN OPOs.

Microchip Nd:YAG and Nd:YVO4 Lasers Pumped by VHG Wavelength-Stabilized Laser Diode

We adopted a single-mode, single-wavelength volume holographic grating (VHG) wavelength-stabilized wavelength laser diode (LD) as a pumping LD for an end-pumped microchip Nd:YAG and Nd:YVO4 lasers we developed during CW and pulse operations. Higher optical-optical and slope efficiencies during CW operation have been obtained than when using a VHG LD experimentally. Output laser power is insensitive to the temperature of the LD when using a wavelength-stabilized LD and can remain stable and almost constant until the temperature of LD increases up to 40°C. The improved optical-optical conversion efficiency of 58% for the Nd:YVO4 laser has been obtained and calculated the output laser power during CW operation and compared it with the experimental results. We found that the output laser power of the Nd:YVO4 laser using the VHG wavelength-stabilized LD was more than twice as high as that using an LD without VHG. When the ambient temperature increases, the difference in output laser power should be large. In the future, a low-cost end-pumped microchip laser that does not require a temperature control should be developed.

Narrow linewidth 2.1 μm optical parametric oscillator with intra-cavity configuration based on wavelength-locked 878.6 nm in-band pumping

We report on an intra-cavity optical parametric oscillator (OPO) based on MgO-doped periodically poled lithium niobate (MgO:PPLN) crystal in-band pumped by a wavelength-locked 878.6 nm laser diode (LD). A narrow linewidth 2.1 μm laser output is obtained by using a reflection volume Bragg grating (VBG). The stability of the resonator under high pump power and the spot mode matching of the parametric laser oscillation process are considered comprehensively to determine the optimal cavity parameters. In the experiment, a narrow linewidth of 2.1 μm maximum output power of 4.7 W is obtained with the pulse duration of 8.55 ns, the linewidth of 1.89 nm at 80 kHz repetition rate, corresponding to the maximum optical-optical conversion efficiency of 11.6%.

Passively Q-Switched Tm: YAP Laser with a WSe2 Saturable Absorber

In this paper, WSe2 nanosheets were prepared and demonstrated to have non-linear absorption characteristics that were saturated at about 2 μm. A passively Q-swithched (PQS) Tm:YAP laser was perfectly implemented with the Wse2 nanosheets as a saturable absorber (SA). In PQS mode, an average output power of 1.01 W with a pulse duration of 1.7 μs at 166.7 kHz was achieved with a pump power of 12.1 W, corresponding to an optical-optical conversion efficiency of 8.3%. A peak power of 3.88 W was acquired from a PQS Tm: YAP laser.

Compact CW Nd:YVO4/PPMgLN green laser

A compact and reliable linear-beam Nd:YVO4/PPMgLN green laser pumped by an edge-emitting laser diode array (24 separate emitters with an overall length of 480 μm and a gross power of 45 W at 807.1 nm) is achieved. The independent 24-edge-emitting array can achieve poor spatial coherence and effectively reduce laser speckle effect. In the air-cooled (water-cooled) condition, the maximum output power is 8.64 W (11.10 W), the optical-optical conversion efficiency is 24 % (25 %), and the power variation is less than 3 % (2 %) for 1 h (3 h).

Stable all-fiber passively Q-switched erbium-doped fiber laser based on plasmonic Zn doped CuGaO2 nanoplates

In this letter, we synthesized p-type Zn doped hexagonal CuGaO2 (CGZO) nanoplates (NPs) by hydrothermal reaction and utilized the nonlinear optical properties of these plasmonic NPs to realized stable passively Q-switched erbium-doped fiber laser output. We achieved tunable saturable absorbers (SAs) by changing the doping ratio of CGZO NPs. With the increase of the doping ratio, pulse duration decreases from 2.532 μs to 2.276 μs and the optical-optical conversion efficiency of the Q-switched laser increases from 1.36% to 1.70%. Our result suggests that CGZO is promising to allow tunable SAs to generate passively Q-switched fiber lasers.