Output Mirror Transmission Research Articles

Characterization and mid-infrared laser operation in Er:CaF2 single crystal fiber grown by the laser heated pedestal growth method

Er:CaF2 crystal, characterized by low doping and high efficiency, is a suitable material for single-crystal fiber (SCF). 3 at.% Er:CaF2 SCFs were grown using the laser heated pedestal growth (LHPG) method. Significant oxidation-induced whitening phenomena were observed during growth. Increasing the growth rate helped mitigate further deterioration due to oxidation. This is likely because higher growth speeds allow the SCF to quickly move away from temperature ranges conducive to oxidation. As oxidation progressed, the phonon energy of 3 at.% Er:CaF2 SCF increased, causing the emission intensity at ∼ 1 μm to decrease from 77 % in the initial source rod to 6 % in the fully whitened state. Additionally, the lifetime of the 4I11/2 level decreased by approximately 10 times, from 8.988 ms to 0.822 ms. Continuous laser output at ∼ 2.8 μm was achieved using the transparent portion of 3 at.% Er:CaF2 SCF. With an output mirror transmission of 2 %, a maximum output power of 251 mW and a slope efficiency of 15.9 % were obtained. The laser experiment demonstrated the potential application of LHPG-grown Er:CaF2 SCF in ∼ 2.8 μm lasers, but further performance enhancement requires additional strategies to address oxidation issues. This work provides valuable insights into the growth of Er:CaF2 SCF using the LHPG method.

28.02 W LD side-pumped CW laser operated at 2.8 µm in YSGG/Er:YSGG/YSGG crystal.

We demonstrated a 978 nm laser diode (LD) side-pumped YSGG/Er:YSGG/YSGG composite crystal with a size of Ф 3 mm × 65 mm and continuous-wave (CW) mode. By optimizing resonator length and output mirror transmittance, a maximum output power of 28.02W is generated, corresponding to slope efficiency of 17.55% and optical-optical efficiency of 12.29%, respectively. The thermal focal lengths are obtained by resonator stability condition. The laser wavelength is centered near 2.8 µm. Moreover, the beam quality factors M x2/M y2 are fitted to be 8.14 and 7.35, respectively. The above results indicate that a high-performance 2.8µm CW laser can be achieved by LD side-pumped YSGG/Er:YSGG/YSGG composite crystal with excellent heat dissipation ability, which promotes effectively the development and applications of the mid-infrared solid-state lasers.

Dual-wavelength collaboratively pumping scheme for a 3.9 µm continuous-wave Ho:YLF laser

A dual-wavelength collaboratively pumping scheme is proposed to realize the efficient operation of a 3.9 µm continuous wave Ho:YLF laser. An 888 nm laser is used to excite ions from the 5I8 ground-state manifold to the 5I5 laser’s upper manifold. Another 2.1 µm laser is used to excite ions from the 5I6 laser’s lower manifold to the short-lived 5I4 manifold to eliminate the self-terminated effect of 3.9 µm laser oscillation. Numerical simulation of 3.9 µm laser output performances is carried out, based on the developed rate equations. Simulation results indicate that the dual-wavelength collaboratively pumping scheme is feasible to realize the highly efficient output of the 3.9 µm continuous wave Ho:YLF laser. The relationship between the pump power for 888 nm and 2.1 µm laser sources is analyzed to obtain the optimal output. Furthermore, the impacts of crystal doping concentration, crystal length, output mirror transmittance, and important energy-transfer processes on the laser output performances are also analyzed. The dual-wavelength collaboratively pumping scheme provides beneficial guidance for the generation of a 3.9 µm high-power continuous-wave laser in an Ho:YLF laser.

An infrared passively Q-switched laser based on graphene/BN heterojunction

Passively Q-switched solid-state lasers (PQSL) can obtain output lasers with narrow pulse widths and high peak powers, where play a vital role in the information society. Saturable absorbers (SA) are an essential part of passively Q-switched solid-state lasers. In this paper, we demonstrated 2 μm passively Q-switched (PQS) solid-state laser based on a graphene/BN heterojunction saturable absorber. In the experiments, we used two output mirrors with transmittance of 1.5 %/2.5 % for comparative study. We also used monolayer graphene as saturable absorber for experiment to compared with graphene/BN saturable absorber. The experimental results showed that the best passively Q-switched operation was achieved with the graphene/BN heterojunction saturable absorber at output mirror transmittance of 1.5 %. When the maximum absorption pump power was 1.49 W, the maximum average output power was 38 mW, corresponding with a slope efficiency of 5.4 %. At this point, the minimum pulse width was 1.56 μs, corresponding with a repetition frequency of 52 kHz. The single pulse energy and the peak power were calculated to be 730.36 nJ and 466.96 mW, respectively. The center wavelength of the PQS laser was 2066.8 nm. The experimental results showed that graphene/BN heterojunction was a promise saturable absorber in the field of 2 μm passively Q-switched solid-state lasers.

Temperature distribution measurement inside an Er:Yb:Lu2Si2O7 crystal under 1.55 μm laser operation

Based on the fluorescence intensity ratio technique, the temperature distribution inside an Er:Yb:Lu2Si2O7 crystal was measured in real time when a 1.55 μm laser was operating. The polarized green up-conversion fluorescence in 500–580 nm of the crystal generated simultaneously under laser operation was used as the temperature probe. At a pump beam waist diameter of 400 μm, the highest temperature inside the crystal reached 507 K when the incident pump power and output mirror transmission were 11.13 W and 1.3%, respectively. The experimental result was compared with the theoretical temperature distribution inside the crystal simulated by the finite element analysis method, and the difference between them was analyzed.

Preparation of continuously tunable orthogonal squeezed light filed corresponding to cesium D<sub>1</sub> line

The non-classical light resonance on the cesium D<sub>1</sub> (894.6 nm) line has important applications in solid-state quantum information networks due to its unique advantages. The cesium D<sub>1</sub> line has a simplified hyperfine structure and can be used to realize a light-atom interface. In our previous work, we demonstrated 2.8-dB quadrature squeezed vacuum light at cesium D<sub>1</sub> line in an optical parametric oscillator(OPO) with a periodically poled KTP(PPKTP) crystal. However, the squeezing level is relatively low, and the tunability that has practical significance for squeezed light has not been further investigated. Theoretically, the increase of the transmittance of output mirror and the decrease of the intra-cavity loss of the OPO can improve the squeezing level. Here, we use super-polished and optimal coating cavity mirrors to improve the nonlinear process in OPO. We prepare 447.3 nm blue light from 894.6 nm fundamental light by a second harmonic generation cavity (SHG). The SHG is a two-mirror standing-wave cavity with a PPKTP crystal as the nonlinear medium. The power of generated blue laser is 32 mW when the incident infrared power is 120 mW. Using the blue light to pump an OPO, we achieve quadrature squeezed vacuum light at cesium D<sub>1</sub> line. The OPO is a two-mirror standing-wave cavity with a PPKTP crystal. The threshold of OPO is reduced to 28 mW. The squeezing level of generated quadrature squeezed vacuum light is increased to 3.3 dB when the pump power is 15 mW. Taking into account the overall detection efficiency, the actual squeezing reaches 5.5 dB. We inject a weak signal beam into the OPO cavity to act as an optical parametric amplifier (OPA), and test the tunability of squeezzed light. The blue light and the squeezed light are tuned by using a low-frequency triangular wave signal to scan the Ti: sapphire laser. Gradually increasing the amplitude of the scanning triangle wave signal, the generated bright squeezed light can be continuously tuned over a range around 80 MHz without losing the stability of the whole system. The generated squeezed light offers the possibility for the efficient coupling between the non-classical source and solid medium in the process of quantum interface.

Single longitudinal-mode passively Q-switched 1537 nm Er:Yb:Lu2Si2O7 pulse microchip laser.

A single longitudinal-mode passively Q-switched 1537 nm pulse microchip laser was realized in an Er:Yb:Lu2Si2O7 crystal. The effects of the pump beam diameter and output mirror transmission on pulse characteristics of the Er:Yb:Lu2Si2O7 microchip laser were investigated, when a Co2+:MgAl2O4 saturable absorber with an initial transmission of 95% was used. At an absorbed pump power of 3.4 W, a 1537 nm single-longitudinal-mode pulse laser with energy of 25.8 µJ, repetition frequency of 0.89 kHz, duration of 4.3 ns, and peak output power of 6.0 kW was obtained, when the pump beam diameter and output mirror transmission were 420 µm and 3.0%, respectively. The beam quality factor of output laser with TEM00 mode was less than 1.3.

Generation of two identical ns laser pulses at single s spacing by switching output mirror transmission

Generation of two identical ns laser pulses at single s spacing by switching output mirror transmission

Energy conversion of multi-optical parametric oscillation based on time-dependent split-step integration methods in MgO:APLN

In a multi-optical parametric oscillator by pulse pumping, energy conversion process for 1.57 μm and 3.84 μm parametric light can be expressed by time-dependent wave equations. The split-step integration method is used to solve the equations. By analyzing the simulation results of the output waveform for the multi-optical parametric amplifier, it is confirmed that back conversion and mode competition are the important factors affecting the multi-optical parametric oscillation. The 1.57 μm and 3.84 μm parametric light in an external cavity multi-optical parametric oscillator are simulated under different output mirror transmittances, crystal working lengths and cavity lengths. The conversion efficiency of 1.57 μm and 3.84 μm increase with the output mirror transmittance increasing, which means that the conversion efficiency can be adjusted by changing the parametric light transmittance of the output mirror. There exist an optimal crystal working length and a cavity length in the external cavity multi-optical parametric oscillator. The experiment on external cavity multi-optical parametric oscillator is carried out. The conversion efficiency of 1.57 μm and 3.84 μm parametric light are consistent with the theoretical values. The energy conversion process in the multi-optical parametric oscillator can be simulated by this method, which could be used for optimizing the multi-optical parametric oscillator and increasing the parametric conversion efficiency.

Diode-pumped high-efficiency passively Q-switched Yb:CaYAlO4 laser

We experimentally demonstrated a high-efficiency passively Q-switched Yb:CaYAlO4 (Yb:CYA) laser based on a semiconductor-saturable absorber mirror (SESAM), and the output characteristics of the laser including the average output power, repetition frequency, pulse duration, pulse energy and pulse peak power were investigated by adopting output mirrors with different transmittances. When the transmittance of the output mirror was 5% and the pump power was set at about 7.76 W, a maximum average output power of as high as 2.480 W was achieved with a slope efficiency and light-to-light efficiency of the Q-switched Yb:CYA laser of up to 37.1% and 31.2%, respectively.

A optimized diode-pumped continuous-wave laser with novel Nd:GdLaNbO4 mixed crystal

A diode-pumped continuous-wave (CW) laser with a novel Nd:GdLaNbO4 mixed crystal at 1065 nm was demonstrated. The influence of various parameters on CW output performance was investigated theoretically and experimentally, including the transmission of output mirror, the resonance length and the focusing radius of pump light. When the resonator length was 40 mm and the focusing radius of pump light was 256 μm, the maximum output power of 3.06 W was obtained with optimum output mirror transmission of 20% at absorbed pump power of 12.24 W. The corresponding slope efficiency was 29.1%.

Diode-pumped acousto-optically Q-switched laser with Nd3+ doped GdYNbO4 mixed crystal

A laser diode pumped acousto-optically (A-O) Q-switched laser based on an innovative Nd:Gd0.69Y0.3NbO4 mixed crystal was presented for the first time. After optimizing output mirror transmission, the pulsed Nd:Gd0.69Y0.3NbO4 laser performances under controllable modulation rates of 10 kHz and 20 kHz were illustrated . At the absorbed pump power of 10.5 W and the modulation rate of 10 kHz, the shortest pulse duration was measured to be 29.1 ns and the corresponding pulse peak power was 4.95 kW.

Metasurface-assisted orbital angular momentum carrying Bessel-Gaussian Laser: proposal and simulation

Bessel-Gaussian beams have distinct properties of suppressed diffraction divergence and self-reconstruction. In this paper, we propose and simulate metasurface-assisted orbital angular momentum (OAM) carrying Bessel-Gaussian laser. The laser can be regarded as a Fabry-Perot cavity formed by one partially transparent output plane mirror and the other metasurface-based reflector mirror. The gain medium of Nd:YVO4 enables the lasing wavelength at 1064 nm with a 808 nm laser serving as the pump. The sub-wavelength structure of metasurface facilitates flexible spatial light manipulation. The compact metasurface-based reflector provides combined phase functions of an axicon and a spherical mirror. By appropriately selecting the size of output mirror and inserting mode-selection element in the laser cavity, different orders of OAM-carrying Bessel-Gaussian lasing modes are achievable. The lasing Bessel-Gaussian0, Bessel-Gaussian01+, Bessel-Gaussian02+ and Bessel-Gaussian03+ modes have high fidelities of ~0.889, ~0.889, ~0.881 and ~0.879, respectively. The metasurface fabrication tolerance and the dependence of threshold power and output lasing power on the length of gain medium, beam radius of pump and transmittance of output mirror are also discussed. The obtained results show successful implementation of metasurface-assisted OAM-carrying Bessel-Gaussian laser with favorable performance. The metasurface-assisted OAM-carrying Bessel-Gaussian laser may find wide OAM-enabled communication and non-communication applications.

940 mW 1564 nm multi-longitudinal-mode and 440 mW 1537 nm single-longitudinal-mode continuous-wave Er:Yb:Lu2Si2O7 microchip lasers.

An Er:Yb:Lu2Si2O7 microchip laser was constructed by placing a 1.2mm thick, Y-cut Er:Yb:Lu2Si2O7 microchip between two 1.2mm thick sapphire crystals, in which input and output mirrors were directly deposited onto one face of each crystal. End-pumped by a continuous-wave 975.4nm diode laser, a 1564nm multi-longitudinal-mode laser with a maximum output power of 940mW and slope efficiency of 20% was realized at an absorbed pump power of 5.5W when the transmission of output mirror was 2.2%. When the transmission of the output mirror was increased to 6%, a 1537nm single-longitudinal-mode laser with a maximum output power of 440mW and slope efficiency of 12% was realized at an absorbed pump power of 4.3W. The results indicate that the Er:Yb:Lu2Si2O7 crystal is a promising microchip gain medium to realize a single-longitudinal-mode laser.

Theoretical study of the characteristics of a continuous wave iron-doped ZnSe laser

A theoretical model describing the dynamic process of a continuous-wave Fe2+:ZnSe laser is presented. The influence of some of the operating parameters on the output characteristics of an Fe2+:ZnSe laser is studied in detail. The results indicate that the temperature rise of the Fe2+:ZnSe crystal is significant with the use of a high power pump laser, especially for a high doped concentration of crystal. The optimal crystal length increases with decreasing the doped concentration of crystal, so an Fe2+:ZnSe crystal with simultaneous doping during growth is an attractive choice, which usually has a low doped concentration and long length. The laser pumping threshold is almost stable at low temperatures, but increases exponentially with a working temperature in the range of 180 K to room temperature. The main reason for this phenomenon is the short upper level lifetime and serious thermal temperature rise when the working temperature is higher than 180 K. The calculated optimum output mirror transmittance is about 35% and the performance of a continuous-wave Fe2+:ZnSe laser is more efficient at a lower operating temperature.

Investigation on the effect of output mirror transmission in WS2-based red-light passively Q-switched Pr:ZBLAN all-fiber lasers.

We report the experimental investigation of visible passively Q-switched Pr3+-doped all-fiber lasers with tungsten disulfide (WS2) saturable absorber, where red-light short-pulse generations from different output mirror transmissions are systemically characterized. The proposed simple and compact all-fiber linear cavity was constructed by a fiber-pigtail-based blue laser-diode pump, a Pr3+-doped fluorozirconate glass active fiber, and the fiber end-facet mirrors. Integrating a free-standing layered WS2 film into the laser cavity initiated the Q-switching operation. Stable microsecond-duration output pulses with kilohertz repetition rates are achieved, corresponding to a few mW/nJ average output power and single-pulse energy. The comparisons on red-light Q-switched output parameters for output transmissions of both ∼40% and ∼80% are performed. This work could provide a useful guideline to manipulate the output performance of visible pulsed all-fiber lasers for various practical applications.

Evaluation of the performance of a Ho: Sc2SiO5 laser pumped by a Tm:YAP laser

A continuous-wave 0.5 % Ho3+-doped Ho:Sc2SiO5 (Ho:SSO) laser output at 2112 nm pumped by a Tm:YAP laser is reported. The Ho:SSO bulk crystal was grown by the Czochralski technique. A maximum laser power of 3.72 W was obtained with a slope efficiency of 32.9%, when the transmittance of output mirror was 30%. In this experiment, two output mirrors with different transmittance were also researched. The output spectra of Ho:SSO laser with different output mirrors are also given. The M2 factor is found to be 1.29. In addition, the absorption and emission spectra are given in this paper.

Theoretical model of simultaneous dual-wavelength laser based on intra-cavity pumping

In this paper, the theoretical modeling of intra-cavity pumped laser used to simultaneously output quasi-three-level laser and four-level laser is proposed. Due to the two laser generating in different gain medium, the gain competition can be avoided. In the modeling, the plane wave approximation is employed, and the analytical expressions of the output power of dual-wavelength lasers are derived. The output characteristics are obtained by numerically simulating, and the impact of changing some critical parameters on the output characteristics are investigated. It is found that by increasing the absorption coefficient of the second gain medium at quasi-three-level radiation, or reducing the output mirror transmittance of the laser, the output power of four-level laser will be promoted, while the output power of quasi-three-level radiation will be turned lower.

Passive Q-switching of a diode-pumped 1520 nm Er:Yb:YAl3(BO3)4 micro-laser with a Co2+:Mg0.4Al2.4O4 saturable absorber

Using an Er:Yb:YAl3(BO3)4 crystal as the gain medium and a Co2+:Mg0.4Al2.4O4 spinel crystal as the saturable absorber, an efficient passively Q-switched 1520 nm pulse laser was realized in a plano–plano cavity end-pumped by a 970 nm diode laser. At an absorbed pump power of 14.8 W and output mirror transmission of 4.6%, a 1520 nm pulse laser with 11.1 μJ energy, 16 ns duration and 27 kHz repetition rate was obtained, which resulted in about 0.7 kW output peak power. Furthermore, the influence of the output mirror transmission on the pulse energy, duration and repetition rate was also investigated.

Compact, efficient diode-end-pumped Tm:Sc2SiO5 2 μm laser

Efficient laser emission at 2μm is demonstrated from Tm:Sc2SiO5 crystal under end-pumping with a continuous wave (cw) diode laser at 790nm. A maximum output power of 1.02W is obtained for the incident pump power of 6.78W, corresponding to an optical-to-optical efficiency with respect to the incident pump power of 14.7%. At this output level the spectrum of emission was centered at 1976nm with a broad bandwidth of 28nm. The laser slope efficiency with respect to the incident pump power was 16.1%. Influence of the output mirror transmittance or of the Tm:Sc2SiO5 crystal temperature on the laser output performance is investigated.