This PDF file contains the front matter associated with SPIE Proceedings Volume 11544, including the Title Page, Copyright information, and Table of Contents.

We have proposed and implemented an all-optical passive synchronization fiber laser system, which was used to facilitate high-performance coincidence frequency upconversion detection for infrared photons. Thanks to the intensive peak power and spectro-temporal pulse engineering, the conversion efficiency could be boosted up to 80% for near- and mid-infrared signal photons. Meanwhile, the background noise was substantially suppressed by confining the pump-induced noise within a narrow excitation window. The demonstrated ultra-sensitive upconversion detector would find promising applications in remote sensing, long-distance ranging and trace detection.

Optical frequency comb has revolutionized the approach to molecular spectroscopy. Here, dual-comb spectroscopy with two asynchronous electro-optic frequency combs tunable in the mid-infrared molecular fingerprint region will be reported for molecular sensing with sub-Doppler-limited spectral resolution and broad bandwidth (more than several THz within a single-shot measurement). Also a three-dimensional (3D) hyperspectral imaging technique based on femtosecond laser filamentation will be demonstrated. The feasibility of laser-induced filamentation for simultaneous detection and identification of multiple gas-phase species in a flame and the potential of the technique for information-rich 3D hyperspectral imaging with both high spatial and spectral resolution will be discussed.

A passively Q-switched dual-wavelength laser with coaxial diode end-pumping configuration is demonstrated. A theoretical model was built to simulate the dynamic process of dual-wavelength laser pulse generation. The experiment was performed with Nd:YVO₄/Nd:GdVO₄ composite laser crystals and a Cr⁴⁺:YAG absorber. The continuous-wave and Q-switched output power reached 3.48 W and 607 mW, respectively, under the maximum LD pump power of 8.0 W, corresponding to optical-to-optical conversion efficiencies of 43.5% and 7.6%. The power ratio between 1064.4 nm and 1063.5 nm could be tuned by varying the pump wavelength to balance the gains in two laser crystals.

High power fiber laser is of importance for a wide range of scientific and industrial processes but the transmission distance is till restricted because of stimulated Raman scattering (SRS). We research here on the mitigation of the SRS in highpower fiber laser systems by long period fiber gratings (LPFGs) for longer laser delivery distance. A broadband and high attenuation LPFG is carefully designed and fabricated by a CO₂ based inscription system. It has been proven effective in extending delivery distance due to its filtering effect of Raman signal.

The imaging systems are widespread observation tools used in the national defense, industry and a number of aspects in science and technology. The CMOS image sensors which serve as the core part of optical imaging systems and detecting systems, are highly susceptible to laser interference and destruction. Therefore, it is of great theoretical and practical significance to study the damage characteristics of CMOS image sensor. There are many researches on the damage phenomena of CMOS image sensors irradiated by continuous laser, ns-laser, ms-laser and fs-laser, but the damage effects of CMOS irradiated by the hundred picoseconds fiber laser are few investigated. In this work, we used an all-fiber MOPA ps-pulsed laser system which generates pulse width of 226.5 ps and average power of 20 W with high beam quality and pulse stability to irradiate the CMOS at repetition rate of 9.6 MHz and 2.4 MHz. The experimental results showed that with the increase of laser power density, the phenomena of over saturation effect, saturated crosstalk effect, black line damage and black lines semi-cross damage appeared at different repetition rates. And the measured threshold and damage mechanism of CMOS were studied. Besides, based on the hydrodynamics theory, the laser-induced plasma density and temperature distribution of various materials (aluminum, copper and silicon) irradiated by the ps-laser were simulated, which provide a theoretical basis for the interaction of metals and semiconductors by the hundred picoseconds fiber laser

Apart from parameter-invariant stationary solitons, numerous nonlinear systems support breathing dissipative solitons (DSs), manifesting themselves as nonlinear waves in which energy concentrates in a localized and oscillatory fashion. In this talk, we review our recent results and advances on breathing DSs. By employing ultrafast laser setups whose outputs are spectrally and temporally analysed in real time, we unveil rich dynamics of breathing DSs in mode-locked fibre lasers. These include establishes a general, deterministic route to induce breathing DSs in normal-dispersion mode-locked fibre lasers, the observation of breather explosions, breather molecules, and molecular complexes in fiber lasers. Numerical simulations based on the complex Ginzburg-Landau equation confirm our experimental observations. These results not only carry significance from an application perspective, but also contribute more broadly to the fundamental understanding of dissipative soliton physics.

Single frequency solid state lasers operating at eye-safe wavelengths have important applications in many fields. Three single frequency ceramic lasers are reported. 1. High-power 1645 nm monolithic Er: YAG ceramic nonplanar ring oscillator (NPRO). 2. High-energy single-frequency Er:YAG ceramic laser. 3. High-energy 2090 nm single-frequency, Q-switched Ho:YAG ceramic laser.

In the last decades, the world has been confronted with increasingly severe threats caused by small drones, especially for security of important places such as military bases and crucial activities in public areas. In comparison with traditional projectile weapons, high-energy laser weapons are especially suitable for countering such threats due to its precise and scalable effect with extremely low collateral damage. This paper presents a systematic design method of anti-drone laser weapons. First, this paper analyzes the system’s requirements. Secondly, describes the damage capability of high-energy laser weapons, presents how to determine the main parameters of the laser weapon system. Finally, for maneuverable deployment, this paper discusses the power supply for laser and cooling equipment, and shows how to reduce the power supply requirement and the system mass.

A radio-frequency (RF) intensity-modulated light source at 532 nm was built for underwater ranging. The intensity of a narrow-linewidth laser at 1064 nm from a NPRO (Non Planar Ring Oscillator) was modulated via a Mach-Zehnder electrooptical modulator. The modulation frequency was tuned from 10 MHz to 2.1 GHz. The intensity-modulated light was amplified via a 2-stage laser diode-pumped Yb³⁺ doped large-mode-area fiber amplifier. A 15 mm long magnesium oxide doped periodically-poled lithium niobate (MgO: PPLN) nonlinear crystal was used to convert the 1064 nm light into 532 nm light via frequency doubling. The maximum output power at 532 nm was 2.56 W, the highest efficiency from the fundamental to second harmonic generation (SHG) was 22.6%. The watt level 532 nm light source was applied in underwater ranging experiments. Different modulation frequencies were applied to measure the distance of an object in the water. The turbidity of the water was changed by adding Mg(OH)₂ powder, ranging accuracy of 6 cm was obtained at 2.5 m distance when the attenuation coefficient of the water was 1.72 m^-1. In turbid water, higher modulation frequency was preferable for obtaining higher ranging accuracy.

We experimentally demonstrate that temporally confined spatial solitons can be realized by space-time coupled propagation of strong femtosecond pulses in a nonlinear optical resonator, consisting of periodic layered Kerr media (PLKM). A universal relationship between the characteristic beam size and the critical nonlinear phase of the solitary modes is revealed, defining different regions of soliton stability. Taking advantage of the unique characters of these solitary modes, we demonstrate supercontinuum generation and pulse compression of initially 260 μJ, 170 fs pulses down to 22 fs in a single-stage PLKM resonator with an efficiency >90%.

A theoretical thermal load model is built to optimize the operation of the Yb:YAG disk laser with zero thermal load. The influences of the number of pump passes and thickness of gain medium on the absorption efficient, optical-to-optical efficiency and input pump power intensity are investigated in detail. And the optimal number of pump passes and thickness of gain medium are delivered based on the model.

Diffractive optical element is used to realize single-aperture output for passive coherent combining of 8-channel fiber laser. Using this system, we demonstrated the far-field coherent visibility, output spectrum and beam quality after coherent combining. Experimental results show that phase noise will cause the mode frequency to change under multi-channel conditions. However, the beam quality and the coherent visibility after coherent combination do not change significantly. The far-field coherence visibility reached 98.6%, the beam quality M²=1.21, and the diffraction limit magnification factor β reached 1.98. This shows that in the presence of low phase noise, even if the number of channels is increased, a coherent combined output with high beam quality can be obtained.

Stimulated Brillouin scattering (SBS) is one of the mainly factors those limit the output power in narrow-linewidth highpower fiber laser systems. Here, we propose and demonstrate a novel method for the suppression of SBS in optical fibers using a tilted fiber Bragg grating (TFBG). With a TFBG being inserted between a single-mode fiber (SMF) amplifier and a 150-meter-length single-mode energy-transmitting fiber, not only the backward Stokes wave is rejected, but also an obvious increasing of the SBS threshold is observed with a value of 1.2 times that without the TFBG, which increases the effective laser output power by about 18 %. This work provides a new idea for SBS suppression in fiber. It is very useful for the further power scaling of high-power narrow bandwidth all-fiber lasers.

We investigated laser output characteristics depended on a discharge starting voltage, gas medium and a repetition rate in a longitudinally excited CO₂ laser. A discharge tube with an inner diameter of 16 mm and a length of 80 cm was applied a high voltage with the rise time of about 200 ns. All laser pulse waveforms were a short laser pulse with a spike pulse and a pulse tail. In the 1:1:2 mixture of CO₂/N₂/He and at the repetition rate of 300 Hz, the laser energy was increased with the discharge starting voltage of up to 40.3 kV. However, in the 1:1:2 mixture of CO₂/N₂/He and at the repetition rate of 600 Hz, the laser energy was saturated with the discharge starting voltage of about 28.6 kV or more. The maximum energy was 14.2 mJ at a repetition rate of 600 Hz and a discharge starting voltage of 28.8 kV.

Laser technology and laser system has more and more important implication in spacecraft engineering. But different from ground environments, space laser system will encounter space environments include vacuum, extreme temperature and thermal cycling, vibration, space radiation environments such as electron, proton, heavy ions, ultraviolet, contamination, and so on. These space environments may have damage or threaten to the space laser system, especially to their optical devices. In this paper, space environments and effects are introduced firstly, and then the influence of space environments such as vacuum, temperature, energetic particles, contamination and vibration on space laser system are analyzed. At last, some advices are proposed to improve the reliability of space laser system are given.

The thin-disk shape laser crystal is the core component of the thin disk laser. In the experiment, we found that the crystal edge is prone to abnormal high temperature in the operation, which causes the thin disk laser's conversion efficiency to decrease, and even the make crystal cracks. In order to solve this problem, two aspects that may cause this effect are researched during the disc crystal manufacturing process, and finally determined that the splash of solder during the packaging process is the main cause of this problem. In the end, we used the edge chamfering method to eliminate this problem, and the finally obtained thin disk crystal can reduce the temperature by 50% and increase the conversion efficiency by 15% when the laser operates.

Solar-pumped laser using solar radiation as pumping source converts sunlight to laser directly. It has the following advantages over other solid-state lasers: sufficient energy resource, clean and pollution-free, long service life, and low manufacturing costs. Up to now, researches on solar-pumped laser have been limited to the 1 μm band with Nd³⁺ doped gain medium. By analyzing the absorption spectrum of the existing solid-state materials, we have found that Tm³⁺ doped materials have strong absorption in visible light band where the solar radiation is strong. 2 μm eye-safe laser has a greater application prospect in the fields of remote sensing, LiDAR, medical treatment, and space optical communication. In this paper, the absorption spectrum and spectral overlap of two common laser crystals, Tm:YAG and Tm:YAP, with the solar radiation have been analyzed and calculated. The threshold pump power density of these two crystals were calculated as 1.14 Kw/cm³ , 1.434Kw/cm³ respectively. Tm:YAG crystal with lower threshold pump power density was selected as the gain medium and a two-stage pumping model was built. A Fresnel lens was used as the primary solar light concentrator. The secondary concentrator was a conic cavity with a defused high reflection surface. The laser rod with grooved side wall was installed in the conical cavity. Tracepro was used to optimize the whole setup. The work in this paper made a theoretical preparation for experimental research of 2 μm solar-pumped laser.

CO₂ laser is a molecular laser that can excite laser beams in the far infrared range of 9~11μm. It works in both pulsed and continuous modes. Time constant is an important index to ensure thermoelectric dynamic performance. In order to verify that the dynamic performance of WRe film thermocouple is better than that of ordinary K-type thermocouple, it has a fast response and a short time constant. The tset system consists of CO₂ laser, shieldingbox, elliptic mirror, thermocouple, infrared detector and acquisition circuit. A pulsed CO₂ laser with a laser wavelength of 10.6 μm is used as the excitation heat source to act on the thermal junction. Time constant dynamic test was carried out on tungsten-rhenium thin film thermocouples WRe3/25 and ordinary K-type thermocouples with a thickness of micron.The time constant testing method of thermocouple can be intuitively obtained by making a tangent line at the highest point of the response curve, and the intersection point of the tangent line and the horizontal axis of the coordinate is the time constant value of the thermocouple. The experimental results show that the WRe film thermocouple has a faster response time and a smaller time constant. Therefore, the conclusion that this thin film thermocouple has better dynamic characteristics than the ordinary K type thermocouple is verified.