This PDF file contains the front matter associated with SPIE Proceedings Volume 11890, including the Title Page, Copyright information, and Table of Contents.

In this letter, a two-stage phase control technique is proposed to increase the control bandwidth of the target-in-the-loop (TIL) system. In this technique, the first stage phase control is enabled by LiNbO3 phase modulator to compensate the phase noises in the fiber amplifiers, and the second stage phase control is enabled by the liquid crystal (LC) to compensate the phase noises induced by the atmospheric turbulence. We built a TIL coherent beam combining system with 3-channel coherent fiber lasers over a 40 m atmospheric propagation path. In our experiment, the stochastic parallel gradient descent (SPGD) algorithm was employed for phase control. When the phase control system was in the close loop, the performance of laser beam projection was significantly improved, and the phase locking bandwidth for transmitter side phase distortions reached 1 kHz. This method can be used for applications such as energy transmission and free-space optical communication.

To realize the ultrahigh intensity over 10^23 W/cm^2, we carried out the wavefront correction and tight focusing of the CoReLS petawatt laser. By the wavefront correction and tight focusing of the CoReLS petawatt laser with two-stage adaptive optics systems and an f/1.1 (f=300 mm) off-axis parabolic mirror, we obtained a near-diffraction-limited focal spot. The measured peak intensity was (1.1±0.1)×10^23 W/cm2, the first realization of the laser intensity over 10^23 W/cm^2. With the PW laser of intensity over 10^23 W/cm^2, we plan to explore strong field QED phenomena and proton/ion acceleration dominated by the RPA mechanism.

We present a compact diode-pumped Tm/Ho:YLF laser, via integrating the Tm-doped and Ho-doped YLF crystals into a single bulk gain medium. Gain spectral model was developed first to the predict the potential Tm:YLF laser wavelength using different types of output coupling, for enhancing resonant absorption of the Ho:YLF crystal. Further verification were carried out by intra-cavity pumping the Ho:YLF laser with a Tm:YLF laser, where maximum output power of 11.3 W at 2.06 μm with near diffraction limited beam quality was obtained with conversion efficiency of 28.2% by considering the incident 793 nm diode power. In the Tm/Ho:YLF laser, maximum output power of 10.2 W at 2063 nm with power instability of 0.55% was obtained, corresponding to a slope efficiency of 29.6 % and optical conversion efficiency of 25.5%. The results provide a compact, accessible, and efficient Ho laser scheme, with has potential applications in wind lidar, surgeries, material processing, and nonlinear frequency conversion toward the mid-infrared region.

For constructing functional photonic integrated circuits, it is expected to incorporate an efficient and compact laser source into the complementary metal-oxide-semiconductor platform. Monolithic integration of III-V submicron lasers on patterned SOI substrates by means of the aspect ratio trapping method is a promising solution. Here, we have designed submicron lasers with reversed ridge waveguides on patterned Si/SOI substrates by three dimensional finite difference time domain simulation, effectively confining the light into the submicron lasers without removing the top Si layer. The reversed ridge waveguide structure can be formed by extending the III-V materials out of the SiO₂ trench. The high-quality InP reversed ridge waveguide epitaxial structures have been obtained. The results of the simulations show that the optical leakage loss is reduced to the order of 10^-2. This provides a new approach to develop the silicon-based submicron lasers emitting at the telecom bands.

We present results on the first demonstration of self-sweeping effect in a ring Er-doped fiber laser. Reverse self-sweeping (with decreasing wavelength) in a range of ~0.1 nm was obtained. Typical sweeping rate was 4 pm/s, which is sufficiently slower as compared with earlier reported fiber lasers. Dual longitudinal mode self-sweeping (similar to reported earlier in linear cavity Er-doped fiber laser) is obtained. The laser generates sequentially long overlapping pulses. Frequency of each subsequent pulse increases by one inter-mode spacing. However, the typical duration of dual-mode operation is ~10 ms, which is one order longer than in previous works. We demonstrated that increase in pump power causes deceleration of sweeping and elongation of dual-mode pulses up to 500 ms. The developed source can be used for fiber sensor interrogation.

We proposed a simple O-shaped cylinder all-fiber-integrated laser without inter-cladding-power-strippers (CPS) based on a quasi-bidirectional pumping scheme. The fiber grooves were inscribed on the outside of an O-shaped aluminium cylinder with both straight and curved tracks. The curved track with a diameter of 10 cm could suppress the high order modes and keep a stable beam quality with the increases of output power, while the straight parts improve the robustness for fusion points and unpackaged optical components. The simplified configuration of no CPS between the oscillator and the amplifier could also improve the total efficiency. The output power, the optical-to-optical efficiency, the beam quality, and the Raman suppression are systematically investigated. It is verified that this design introduces a practical way to simultaneously improve the transverse mode instability (TMI) and SRS thresholds in a high-power fiber laser system with a simple configuration and high efficiency.

We report a dual-wavelength tunable passively Q-switched Er³⁺ -doped ZBLAN fiber laser at ~3 nm using a bulk PtSe2 as a saturation absorber. Stable pulses were generated for average output power of 504.0 mW at 72.9 kHz repetition rate. The corresponding pulse width and pulse energy were measured to be 1.26 μs and 6.92 μJ, respectively. By tuning the feedback angle of the plane ruled grating, the spectra show simultaneous dual-wavelength pulsed operations with tuning range of 51.5 nm (2745.5-2797.0 nm) at the launched pump of 2.27 W.

We report experimental investigation of PD in Yb-doped fibers. From fluorescence spectra while pumping at 1018 nm and 976 nm, we can attribute the PD to existence of oxygen deficiency centers and its strong dependence on the excited Yb3+ ion density. Furthermore, we investigated the impact of PD on the laser amplification experiment, demonstrating that the tandem pumping at 1018 nm could dramatically reduce the PD-induced background loss compared to the LD pumping at 976 nm due to the low excited Yb3+ density. We will discuss the way to mitigate the PD in high power Yb fiber lasers.

Because of the low thermal conductivity of the mixture gases in an alkali vapor cell, the temperature of the pumping area of an alkali vapor cell can be extremely high than that of other area. Therefore, thermally-induced effects, such as, consumption of atomic alkali, degradation of output power, glass window contamination by the products of the optically chemical reaction between atomic alkali and buffer gases, etc. can be observed in high temperature heated diode pumped alkali lasers (DPALs) in the case of high power pumping. Generally, a flowing diode pumped alkali laser (FDPAL) system is thought to be a useful way to mitigate thermal effects in a DPAL system. In the paper, a mathematical model of a flowing diode pumped cesium laser (FDPCL) was constructed to systematically study the temperature distribution, the flow filed distribution, and the impacts of pressure of the buffer gases on output power of a FDPCL, etc. The laser kinetics, heat transfer, and computational fluid dynamics (CFD) are both taken into account at the same time during the simulation. The multi-physics coupling method was utilized to solve such three physics induced problem during the simulation. It has been demonstrated that the temperature distribution of a FDPCL system depends on the distribution of gas flow filed, a gas flow method can decrease thermal effects in a DPAL system, and the output power of a DPAL can be improved by increasing the velocity of gas flow filed.

The full vector nature of light provides an additional degree of freedom, namely, the angular momentum (AM) which includes both spin angular momentum (SAM) and orbital angular momentum (OAM). This full AM space holds a great promise for multi-dimensional high capacity data modulation and multiplexing in both classical and quantum regimes, confronting the exploding demands for information. The dynamical generation and control of optical vortices carrying SAM-OAM states mainly rely on tabletop optics. Vortex microlasers offer more compact and robust solution. However, the recently developed vortex microlasers either lack reconfigurability or require extremely low temperature operation environment, limiting the potential real world applications. By harnessing the properties of total angular momentum conservation, spin-orbit interaction and optically controlled non-Hermitian symmetry breaking, we demonstrate an on-chip integrated SAM-OAM-tunable vortex microlaser at room temperature, providing up to 5 different SAM-OAM states at a single telecom wavelength. Moreover, by utilizing fast transient optical gain dynamics in semiconductor materials, we experimentally demonstrate the ultrafast control of fractional OAM emission continuously from 0 to +2 in less than 100 ps. Our toolbox of flexible generation and control of vortex emission at a single wavelength provides a feasible route for the development of the next generation of multi-dimensional high capacity information system in both classical and quantum regimes.

We report on high power and efficient laser operation of low scattering loss Tm:Y₂O₃ ceramic fabricated in house via coprecipitation process. The Tm³⁺ ion is pumped directly to the upper energy level of the ~ 2 μm laser transition (³F₄ → ³H₆) using a high power 1620 nm fiber Raman laser. With an optically polished but uncoated sample of 2 at.% doping, the laser generated 11.3 W of TEM₀₀ output power at ~2050 nm for ~19 W of absorbed pump power, corresponding to a slope efficiency of 74.4% with respect to absorbed pump power.

Considering the impact of the pump focal position on the output characteristics in dual-wavelength lasers with coaxially arranged dual crystals, we study on the thermal effects based on two coaxial Nd:YVO₄ crystals with variable pump focal position and incident pump power theoretically and experimentally. The output characteristics and thermal focal lengths were discussed at different cavity lengths using the resonator theories and compared with the monolithic crystal. The performance of the scheme with two discrete crystals when the focal position locates deep at different cavity lengths was also researched and the advantages over single crystal were verified.

We report Q-switched Er³⁺ -doped ZBLAN fiber lasers operating at 2.8 μm based on MIL-68(Al) (MIL: Materials of Institute Lavoisier), for the first time. The nonlinear absorption of MIL-68(Al) was characterized by using a homemade nonlinear absorption measurement system. The modulation depth, non-saturable loss, and saturation peak intensity are determined to be 24.43 %, 58.63%, and 0.0335 GW/cm², respectively. A piece of 6 mol.% multimode Er³⁺ -doped ZBLAN fiber was used as the gain medium. The maximum average output power as high as 1.18 W was reached with the shortest pulse duration as short as 546 ns at a repetition rate of 106.71 kHz. The corresponding pulse energy and peak power were 11.03 μJ and 20.19 W, respectively. Then, we replaced the gain fiber with a 7 mol.% single-mode Er³⁺ -doped ZBLAN fiber and achieved nanosecond pulses with a pulse duration of 846 ns and average output power of 0.734 W. The corresponding pulse energy and peak power were 3.68 μJ and 4.25 W, respectively. Our work shows that the MIL-68(Al) is a promising stable SA for mid-infrared high-power nanosecond laser pulses generation.

In this work, a self-sweeping Yb-doped fiber laser generating quasi-CW radiation is demonstrated. The laser is based on a ring configuration allowing to form running and standing waves in separate sections of the cavity. The laser generates a sequence of single-frequency (linewidth of ~0.7 MHz) ultra long (~1 ms) rectangular pulses. The laser frequency changes from pulse to pulse by one inter-mode spacing (~10 MHz). The laser signal intensity is quasi-CW signal accompanied by regular bursts generating during frequency change, and the intensity never drops to zero. The features can be useful for long term averaging when measuring weak signals.

A continuous-wave (CW) dual-wavelength laser with coaxial diode end-pumping configuration is demonstrated. A theoretical model was built to simulate the CW output power process of the dual-wavelength laser generation. The experiment was performed with Nd:YVO4/Nd:YAP composite laser crystals. The continuous-wave output power reached 5.28 W under the maximum LD pump power of 15 W, corresponding to optical-optical conversion efficiency of 35.2%. The power ratio between 1064 nm and 1080 nm could be tuned by varying the pump wavelength to balance the gains in two laser crystals.

Using a YVO₄/Nd:YVO₄/YVO₄ composite crystal end pumped by laser diode, we demonstrate the simultaneously Q-switched and mode-locked self-Raman laser at the firststokes wavelength of 1176.07 nm. Its corresponding linewidth was measured to approximately be 0.14 nm. At the pump power of 38 W and the pulse repetition frequency of 50 kHz, the maximum average output power at 1176 nm was obtained to be 1.34 W with the corresponding optical conversion efficiency of 3.6%. The highest pulse energy and the highest peak power were obtained to be 35 μJ and 10.5 kW, respectively. The shortest mode-locked pulse width of the laser was obtained to be ~300 ps with the corresponding repetition rate of mode-locked laser pulse is ~ 1.11 GHz

Ytterbium (Yb³⁺)-doped fiber lasers can offer high-power output with great brightness and excellent beam quality, and have been widely used in many application areas such as material industry, 3D printing, remote free-space communication and optoelectronic countermeasure. Especially in industrial processing field, the requirement for high-power fiber lasers keeps increasing year by year. In this field, the traditional fiber lasers usually deliver output beam with Gaussian intensity. However, according to the practical application experience, the high-power fibers laser with ring beam output reveals unique advantages in industrial processing such as higher initial rate of absorption, faster welding speed, deeper fusion penetration and wider fusion width, and can be used for high-quality welding of mild steel, stainless steel, titanium, red copper and brass. In this letter, we demonstrated a monolithic high-power all-fiberized laser oscillator with power scaling up to 5 kW which had output beam with ring intensity distribution and its output characteristics were carefully studies. The schematic diagram of this fiber laser was shown in Fig. 1. It employed the bidirectional-pump scheme which adopted two pump/signal combiners (PSCs) to coupling the pump energy into the fiber oscillator. One high-reflection fiber Bragg grating (HR FBG) and one output-coupling FBG (OC FBG) constituted the two ends of the oscillator. The gain fiber was a piece of 25/400 μm large-mode-area Yb-doped fiber (LMA YDF). A fiber QBH was fused with the OC FBG for laser output and a cladding pump stripper (CPS) was adopted in between them for removing residual pump power. The backward laser was collected using a useless-laser garbage. By properly adjusting the pump power of forward and backward directions to suppress the transverse mode instability (TMI) and stimulated Raman scattering (SRS), as shown in Fig. 2(a), the maximum output power reached 5080 W and the corresponding pump-to-signal conversion efficiency was calculated to be 68%. Fig. 2(b) was the measured signal spectrum under 5080 W. The central wavelength was located at 1080 nm with a FWHM of 3.6 nm. The intensity of SRS light was 37 dB lower than the 1080 nm signal light. The time-domain characteristics at the maximum output power and the corresponding fast Fournier transformation (FFT) were shown in Fig. 2(c), revealing that no TMI was observed. The beam quality (M2) at the maximum output power was measured to be 2.483 in X direction and 2.514 in Y direction, and was shown in Fig. 2(d). The insert in Fig. 2(d) was the beam intensity distribution at the focal point, which indicated that the signal beam was a standard ring beam and the intensity in annular region was 1.5 times as that in center region. In addition to the tested performance listed above, the fiber laser oscillator worked continuously for one hour and the recorded output power was shown in Fig. 2(e). The figure reveals that the output power was very steady and no obvious power fluctuation was observed.

We have demonstrated a high energy, widely tunable, long-wave mid-infrared optical parametric oscillator based on BaGa₄Se₇ crystal (BaGa₄Se₇-OPO) which was pumped by an economical wavelength of 1.064μm. The BaGa₄Se₇-OPO was designed as a double pass single resonant oscillator (DP-SRO), with the advantages of low threshold and high output. The output energy and conversion efficiency of BaGa₄Se₇-OPO with different cavity lengths were studied theoretically and experimentally. The maximum mid-infrared energy of 611μJ/pulse at 11μm was obtained, and the corresponding optical-to-optical conversion efficiency was 1.53%. A wide tuning range of 8.24-13.3μm was achieved by rotating the BaGa₄Se₇ crystal and it can be well matched with the theoretical calculation.

Full characterization of few-cycle laser pulses is necessary for laser application. FROG is one of the most widely used full characterization techniques so far, and SRSI is another fresh one with attractive capacity. An all-reflective transient-grating based self-referenced spectral interferometry (AR-TG-SRSI) method is proposed for the single-shot characterization of few-cycle near Fourier transform-limited (FTL) laser pulses with a spectral range from UV to mid-IR. What’s more, a simple device FASI is built, which combines the FROG method and the SRSI method based on the same third-order TG effect in a single device. Pulses centered at 800 nm and 1800 nm were characterized by these two devices to verify their capacity. The two devices can characterize few-cycle pulses with a broad spectral range. And can characterize pulse by using the SRSI mode for well-compressed pulses. While, for complete pulses that own large chirp, the TG-FROG mode of the FASI device can also do the work.

High-energy PW laser pulses provide unprecedented extreme conditions which are key tools for exploring frontier fundamental researches. Recently, a new limitation from traditional grating-based pulse compressor appeared during achieve high-energy tens and hundreds PW laser pulses because the damage threshold and maximum size of diffraction gratings are not high or large enough to satisfy the requirement. Here, we propose feasible grating-based pulse compressors that can compress high-energy 100 PW laser pulse with a single beam. It contains two schemes, one is multistep pulse compressor that including pre-compressor, main compressor and post compressor, while the other is asymmetric four-grating compressor that replaces the pre-compressor and main compressor. The proposed novel grating-based pulse compressors increase the maximum bearable input and output pulse energies through modifying their spatiotemporal properties, and the introduced smoothing beam with spatial dispersion can be automatically compensated at the focal plane by using the spatiotemporal focusing technique. In this paper, we use Matlab to theoretically verify the possibility of the new grating-based pulse compressors. The simulation results are extremely consistent with our expectations that the two schemes can effectively smooth the beam by inducing spatial dispersion and effectively achieve 100 PW laser pulse. This creative optical design will simplify the high-energy compressor, improve the stability of PW laser system and ultimately increase the output laser energy, which allows us to explore more frontier fundamental researches.

SO₂F₂ gas is one of the important decomposition products of SF₆ in the GIS gas chamber. Based on the analysis of the chemical composition of the gas, the failure prediction of high-voltage electrical equipment can be realized. The SO₂F₂ gas detection system in the GIS is built based on the second harmonic absorption technology with an inter-band cascade laser with a center wavelength of 3599 nm. The experimental results of the tuning characteristics of the ICL laser show that when the laser works at 35°C and the drive current is 60~100 mA, the emission wavelength of the laser output can cover the wavelength range of 3615.4 nm to 3623.4 nm, which meets the detection requirements of SO₂F₂ gas at 3619.3 nm. The second harmonic detection results show that the gas harmonic absorption intensity increases with the increase of gas concentration, and the fitted linear correlation R² is 0.99563, which has a good positive correlation. Collect 300 sets of data, the collection time is 50 minutes, the relative standard deviation (RSD) is 0.29%, and the system detection limit is 357.56 ppb. This method can provide a new method for the optical detection of SO₂F₂ gas.

Multidisciplinary design optimization (MDO), as an advanced and effective theory and method to solve the design problems of many complex products and systems, has attracted more and more attention. Based on the analysis of product design activities, the effective theory and engineering practice of complex systems are discussed.

We report on a pulsed regime of Raman laser with all-fiber cavity scheme based on a multimode graded-index fiber directly pumped by a CW multimode laser diode. The cavity was performed with 3.7 km 62.5/125 MM graded-index fiber with two FBGs on the both sides of it. Intra-cavity acousto-optic modulator pigtailed with 10/125 fiber allowed to obtain mode locking regime. At 27.19-kHz repetition rate corresponding to the laser cavity round-trip frequency (corresponding to mode-locking regime), stable nanosecond pulses with 6.3 W peak power have been observed at the 1st (1018 nm) Stokes order. The beam quality of generated pulses is greatly improved as compared to that for pump diode (M²<20) reaching M²=2.86 for the 1st Stokes and M²=2.08 for the 2nd Stokes beams.

All-fiber Raman lasers have demonstrated their potential for the efficient conversion of highly multimode pump beams into a high-quality Stokes beams. However, the modal content of these beams has not been investigated yet. Here we apply, for the first time, a mode decomposition technique for revealing intermodal interactions in different operational regimes of CW multimode Raman lasers. Our approach allows for analyzing the output laser radiation in terms of the amplitude and phase distributions of a huge number of excited modes for both the pump and the Stokes beams, which enables a new insight into nonlinear mode coupling processes. The measured contribution of the first three modes of the residual pump beam after overcoming the SRS threshold decreased on average by 25%, whereas the signal beam mainly consists of fundamental mode (40%) and the modes of the first group (20%).