By analyzing the influence of the titanium-sapphire (Ti:S) crystal thermal effect on the laser resonator during the generation of a 689 nm laser, the thermal characteristics of the Ti:S crystal operating near the gain edge were investigated in this letter. On this basis, a Ti:S laser with high conversion efficiency suitable for operation at the wavelength of 689 nm was designed. Benefiting from the quantification of thermal effects, the beam waist size at the center of the Ti:S crystal was precisely controlled. Finally, a single-frequency continuous-wave 689 nm laser with an output power of 3.65 W was achieved, and the corresponding optical-to-optical conversion efficiency was up to 23.1%. Then, after locking the transmission peak of the inserted etalon to the resonance frequency of the resonator, the continuous-frequency tuning range of 17 GHz around 689 nm was realized by scanning the voltage applied to the piezoelectric transducer (PZT) mounted on the cavity mirror. Furthermore, based on the realized single-frequency continuous-wave tunable 689 nm laser source, the absorption spectra of strontium atoms near 689 nm were obtained, which established a promising method for preparing 689 nm laser sources designed for strontium atomic ensembles.

In this paper, a high-power UV-pumped BBO optical parametric oscillator (OPO) is presented by increasing the working temperature of the nonlinear crystal to fasten the color center recovery speed and further decrease the color center density. When the working temperature of the BBO crystal was experimentally increased from 135 °C to 185 °C, the output power was scaled up from 1.20 W to 2.17 W. The repetition rate and pulse width of the signal light were 10 kHz and 5.23 ns, respectively. By rotating the BBO crystal, the wavelength of the signal light was tuned from 409.81 nm to 581.87 nm. To the best of our knowledge, it was the highest output power for the 355 nm UV-pumped II-type critical phase-matched BBO OPO. The results are beneficial for the development of OPOs as well as in industrial and scientific research fields.

For a laser diode (LD) with high output power, it is difficult to precisely and quickly control its temperature because of the large thermal power involved. In this paper, a machine learning-based temperature controller for high-power LDs is reported. It is implemented by developing a back-propagation neural network (BPNN) with an adaptive dynamic adjustment strategy (ADAS) temperature controller which integrates a constant-current-source circuit into the conventional proportional-integral-derivative (PID) temperature-controlling circuit. Compared to the conventional PID controller, the speed of temperature control had been shortened from 1300 s to 350 s, the long-term temperature fluctuation was decreased from ±0.148% to ±0.082%, and the step response time could be decreased from 960 s to 210 s.

Large energy single-frequency nanosecond (ns) near-infrared light source is an essential device in the field of the remote chemical analysis based on the laser-induced breakdown spectroscopy (LIBS). In this paper, a large energy single-frequency ns 824 nm light source with high repetition rate is presented, which is generated from a seed-injection locked optical parametric oscillator (OPO). By optimizing the spot radius of the pump laser and the mode-matching between the pump laser and signal light, the optical parametric generation (OPG) process is effectively eliminated. On this basis, with the assistance of the seed-injection locking, a single-frequency 4 kHz ns 824 nm light source with an output pulse energy and a spectral width of 3.39 mJ and 32.42 MHz is obtained. For the best of our knowledge, it is the largest energy for the single-frequency ns near-infrared light source with the repetition rate of kHz level.

A high-power single-frequency continuous-wave wideband continuously tunable dual-wavelength laser at 1064/532 nm is presented in this paper. Firstly, a thermally insensitive cavity containing a type-I phase-matching LiB3O5 crystal and an uncoated quartz etalon was specially designed, which provided the fundamental condition for the generation of a high-power single-frequency 1064 nm and 532 nm laser. By carefully optimizing the mode matching, the maximal output powers of 13.3 W at 1064 nm and 12.5 W at 532 nm were achieved when the pump power was 63.7 W, and the total optical–optical efficiency of 40.5% was achieved. After the transmission peak of etalon was locked to the oscillating frequency of the resonator, the continuous frequency tuning ranges of the achieved laser were as wide as 26.75 GHz at 1064 nm and 53.5 GHz at 532 nm.

An all-solid-state single-frequency continuous-wave (CW) 355 nm ultraviolet (UV) laser based on a dispersion-compensated doubly resonant resonator is presented in this Letter that is achieved by employing homemade high-stability all-solid-state frequency-correlated dual-wavelength lasers at 1064 and 532 nm and a temperature-controlled type-I critical-phase-matching LiB3O5 (LBO) to act as the fundamental laser source and the nonlinear medium, respectively. The frequency-correlated dual-wavelength single-frequency CW laser supplies the fundamental frequency 1064 and 532 nm lasers with good frequency synchronization. And the temperature-controlled LBO acts as the dispersion-compensation element to realize double resonance of the 1064 and 532 nm laser. Finally, a 4.2 W high-stability 355 nm UV laser is experimentally obtained, and the corresponding total conversion efficiency is up to 20.5%. To the best of our knowledge, this is the highest power reported about single-frequency CW 355 nm UV laser. The presented method can pave a way to develop a compact single-frequency 355 nm UV laser with high output power.

Significance:All-solid-state single-frequency continuous-wave(CW)laser have found extensive applications in diverse domains such as the generation of non-classical light fields,cold atom physics,detection of gravitational waves,and so on,which primarily attributed to their merits of low noise,narrow bandwidth,excellent beam quality,and high power stability.In line with the advancement in science and technology,the output power of the traditional all-solid-state laser(ASSL)cannot satisfy the application requirements of many frontier research fields,so it is necessary to further scale the ASSL power and simultaneously maintain other excellent performance.For the purpose of improving the output power of the ASSL,its pump power has to be primarily elevated.However,with the increasement of the pump power,the laser gain is enhanced,and the non-oscillating laser modes of the ASSL start to oscillate,which results in the mode-hopping or the multi-mode oscillating operation of the ASSL.Moreover,the severe thermal effect of the laser gain medium and its relatively lower damage threshold also further restrict the improvement of the ASSL power.In this paper,an effective method of improving the all-solid-state single-frequency CW laser power via deliberately introducing a nonlinear loss into the resonator was presented.When the nonlinear loss was introduced,the nonlinear loss of the lasing mode was half of that of non-lasing mode,and the non-lasing mode was effectively inhibited,under the mode competition of the laser.As a consequence,the stable single-longitudinal mode operation of the laser can be guaranteed at higher laser gain.In addition,the design of multi-laser-crystal resonator can be adapted to efficiently mitigate the negative impact of the thermal effects of the laser crystal.By combining the nonlinear loss technique and the multi-laser-crystal resonator scheme,the output power of the all-solid-state single-frequency CW laser had been scaled up to 100-watt level and continuously increased. Progress:First,the fundamental principle of mode selection implemented by intra-cavity nonlinear loss is presented.When the nonlinear loss is introduced into the resonator,the nonlinear loss of the lasing mode is half of that of the non-lasing mode,and the non-lasing modes are suppressed effectively under the mechanics of mode competition.Based on the principle above,the physical condition of stable SLM operation for ASSL is proposed.The condition depends on the intra-cavity linear and nonlinear losses,which is experimentally validated by changing the transmission of the output coupler.In the experiment,when the output coupler transmission is 19%,and the temperature of the type-I phase matched nonlinear crystal LBO is 149℃,the maximal output power of 33.7 W for the stable single-frequency 1064 nm laser is realized.On this basis,the intra-cavity round-trip loss of an ASSL is measured precisely by simply changing the temperature of the nonlinear LBO crystal to manipulate the nonlinear loss within the SLM region of the laser.According to the measured results and the oscillating condition of the ASSL,the output coupler transmission of the designed laser as well as its pump power is further optimized and the maximal output power of 50.3 W for the single-frequency 1064 nm laser is obtained. To further increase the output power of the single-frequency laser,the pump power of the laser has to be raised.However,the sever thermal effect of the laser gain medium and its lower damage threshold restrict the continuously increasing of the single-frequency laser power.For the purpose of breaking aforementioned restriction and attaining higher power single-frequency laser,a laser resonator with two identical laser crystals was designed,where the precise mode-reproduction of the two crystals was implemented by a pair of lenses with identical focal length of 100 mm.When the total pump power was 240 W,a single frequency 1064 nm laser with maximal output power of 101 W was realized.In this laser,the focal lengths of the two lenses were fixed,so the laser only would be operated at a given incident pump power,and simultaneously the optical length between the imaging lenses had to be precisely adjusted.To this end,a self-mode-matching laser with four laser crystals in a single resonator was further designed.The total four laser crystals were used for both laser gain media and mode-matching elements.Under an appropriate combination of pump powers on four crystals,a stable CW single-frequency 1064 nm laser with 140 W power was obtained. Conclusions and Prospects:Introducing nonlinear losses within the resonator is a robust way to realize SLM laser output,which has been experimentally proved.With multiple gaining crystals inserted in one cavity,the heat load on each crystal is effectively shared,so more total power is tolerable.With suitable mode matching and mode reproducing in the resonant,a high-power single-frequency CW ASSL has been designed and built which can deliver 140 W single-frequency CW laser,this is to our knowledge the highest SLM ASSL power.The progress in high-power single-frequency ASSL has significantly broadened its potential applications and made substantial contributions to the advancement of related disciplines.

High-power all-solid-state continuous-wave (CW) single-frequency laser with high linear polarization is a significant source for quantum optics and precision measurement. In this Letter, a high-power linearly polarized CW single-frequency laser based on the single-crystal fiber (SCF) master-oscillator power amplifier (MOPA) is presented, in which a homemade 140 W low-noise CW single-frequency laser and a Nd:YAG SCF are firstly employed as the seed laser and the medium of the MOPA, respectively. The mode-matching between the pump laser propagated with waveguide form and the freely propagated seed laser is optimized by considering the influence of the degradations of the polarization and the beam quality. Finally, when the incident powers of the pump and seed lasers are 262.6 W and 126.3 W, respectively, the seed waist radius is optimized to 200 μm. In this case, the output power of the linearly polarized laser reaches up to 208 W, which is the highest output power, to the best of our knowledge. The presented results provide a good reference for implementing a high power and high degree of the polarization and good beam quality laser based on the SCF MOPA.

Objective High-power, high-beam-quality, all-solid-state 355 nm ultraviolet lasers, with their short wavelengths, easy focusability, and high energy characteristics, are being widely applied in precision machining, biomedical, optical manufacturing, and optical sensing fields. The most common technique by which to achieve 355 nm ultraviolet output is the use of a master oscillator power amplifier (MOPA) to amplify 1064 nm seed light through single or multiple stages. This is followed by triple-frequency conversion outside the cavity. However, the overall complexity of the system is not conducive to the design of high-stability ultraviolet lasers. Compared to external frequency tripling technology, the intracavity frequency tripling process can fully utilize the high power density inside the cavity for nonlinear mixing, thereby improving the conversion efficiency, and its compact overall structure and high stability make it an effective means by which to realize the widespread application of high-power all-solid-state 355 nm ultraviolet lasers. To further improve the output power of the 355 nm ultraviolet laser achieved by intracavity frequency conversion technology and to reduce the beam quality factor to a value below 1.2, this study first examines the impact of walk-off on the output power of 355 nm lasers under the same and different optical axis orientations of two nonlinear crystals. Then, walk-off compensation technology between nonlinear crystals is used to effectively compensate for the walk-off phenomenon caused by the mixing of fundamental frequency light and harmonic light in the triple-frequency crystal, thereby increasing the output power of the 355 nm laser to 14.1 W. Methods To obtain a high-power, high-beam-quality, all-solid-state 355 nm ultraviolet laser, a solid-state-state intracavity Nd:YVO4 laser is first designed and manufactured to significantly enlarge the spot radius of the fundamental frequency light at the tripling crystal while ensuring high power output, thereby extending the lifespan of the nonlinear crystal. Then, the second harmonic generated by the type I phase-matching nonlinear lithium triborate (LBO) crystal, has a polarization state perpendicular to that of the fundamental frequency light. The incident fundamental light and the generated second harmonic perfectly satisfy the type II phase-matching conditions of the triple-frequency LBO crystal, achieving the output of a triple-frequency 355 nm laser. On this basis, by comparing the output power of a 355 nm laser with different lengths of the second harmonic crystal, the optimal triple-frequency conversion efficiency is achieved. The study also explores the differences in 532 nm laser output power and beam quality of 355 nm laser under different lengths of the second harmonic crystal and the conditions of the same and different optical axis directions of two nonlinear crystals. Results and Discussions First, frequency conversion is achieved using LBO crystals with 19 mm and 11 mm in length, and the differences in the output power of a 355 nm laser under the same and different optical axis orientations of the two nonlinear crystals are recorded. When walk-off is compensated, the output power of the 355 nm laser reaches 14.1 W, which is 2 W higher than that observed before the walk-off is increased [Fig. 3(a)]. By adjusting the lengths of the different second harmonic crystals, the optimal triple-frequency conversion efficiency is achieved [Fig. 3(b)], indicating that the triple-frequency conversion efficiency is the best when the second harmonic crystal length is 11 mm. The transformation relationship of the 532 nm laser output power with the pump light power is also measured under different lengths of the second harmonic crystal (Fig. 4), similarly indicating that the second harmonic conversion efficiency is the highest under the same second harmonic crystal. Based on this, the differences in the beam quality of the 355 nm laser under compensated and uncompensated walk-off conditions are measured [Fig. 5(a) and Fig. 5(b)], showing that walk-off compensation technology effectively compensates for the walk-off phenomenon caused by the mixing of fundamental frequency light and harmonic light in the triple-frequency crystal, thereby improving both the triple-frequency conversion efficiency and beam quality. At the highest average 35 nm laser output power, the corresponding pulse width is 12.8 ns [Fig. 7(a)], and the beam quality is better than 1.18 (Fig. 5). The power stability (root mean square) at 14.1 W for 10 h is better than 0.9% [Fig. 7(b)]. Conclusions In summary, this study describes the creation of a high-power, all-solid-state 355 nm ultraviolet laser by placing two LBO crystals inside a cavity for second harmonic generation (SHG) and third harmonic generation (THG), respectively. The walk-off compensation technique between the two nonlinear crystals inside the cavity structure is experimentally verified to enhance the output power and improve the beam quality of the 355 nm laser. This ensures that even when the fundamental frequency spot diameter at the triple-frequency crystal reaches 836 mu m, the 355 nm laser can still achieve high power, high beam quality, and highly stable output. An output of 14.1 W for 355 nm pulsed light is obtained with a pump injection power of 96.8 W, corresponding to an infrared-to-ultraviolet light-to-light conversion efficiency of 32.1%, a pulse width of 12.8 ns, a pulse repetition frequency of 35 kHz, and a beam quality of better than 1.18. The power stability (root mean square) at 14.1 W over 10 h is better than 0.9%. The design proposed in this study features a simple system structure, high average power, and good beam quality. It also suggests that for other research using LBO crystals with double-ended vertical cross-sections for tripling frequency, adopting this design will yield higher 355 nm laser output power and conversion efficiency. These characteristics make the laser suitable for widespread commercial applications in fields such as light-emitting diode, liquid crystal display, ceramics, and glass cutting.

All-solid-state tunable lasers have been widely used in many fields including multi-photon microscopy, time-resolved photoluminescence, atomic physics, and so on owing to their broadband output spectrum range, good beam quality, and low noise. To cover the broad fluorescent line of the laser crystal as much as possible, a birefringent filter (BRF) is always the most popular candidate for acting as a tuning element. In this review, the tuning characteristics of BRF and the design rule as well as its progress in practical application are summarized. Especially, it is worth noting that laser crystal itself begins to act as the BRF for wavelength tuning except for its gain characteristic, which has paved a new way for developing a kind of novel tunable laser. We believe that this review will not only provide a valuable reference for the design of BRF but also lay the foundation for developing a new application of BRF.

All-solid-state continuous-wave (CW) single-frequency tunable Ti:sapphire (Ti:S) laser is an important source in quantum optics and atomic physics. However, intracavity etalon (IE) locking is easily influenced by the intensity noise of the pump source in the low frequency band. In order to address this issue, a differential detector with dual-photodiodes (PDs) is designed and employed in the experiment. Both PDs are used to detect the lights of the pump source and the built Ti:S laser, respectively. As a result, the influence of the intensity noise of the pump source on the stability of the IE locking is successfully eliminated and the IE is stably locked to the oscillating longitudinal-mode of the laser. On this basis, a stable CW single-frequency tunable Ti:S laser is realized. The presented method is beneficial to attain a stable single-frequency tunable laser with immunity to the intensity noise of the pump source.

全固态单频连续波钛宝石激光器具有线宽窄、光束质量好、噪声低和稳定性高等优点,尤其是其输出激光波长覆盖了 650～1 030 nm的红光和近红外波段,可以对应多种原子的跃迁吸收线,因而是原子物理、量子通信、拉曼光谱等研究领域中的重要光源.近年来,随着精密测量研究的快速发展以及量子模拟等新型研究的兴起,在关注全固态单频连续波钛宝石激光器的宽输出波段的同时,对钛宝石激光器的转化效率、输出功率、连续调谐能力、稳定特性及噪声特性提出了更高的要求.介绍了以提高全固态单频连续波钛宝石激光器性能为出发点所发展的自注入单向技术、超宽范围调谐技术、连续调谐技术,并综述了近年来所发展的各项技术在全固态单频连续波钛宝石激光器中的最新应用进展.

To realize a stable single-longitudinal-mode (SLM) 1550-nm light source for the generation of non-classical states, a ring auto-pump-depleted singly resonant optical parametric oscillator (SRO) with the assistance of second-harmonic-wave generation (SHG) is designed and built in this Letter. A magnesium oxide doped periodically polarized lithium niobate (MgO:PPLN) crystal and a lithium triborate (LBO) crystal are employed as the optical parametric downconversion (OPDC) and SHG crystals, respectively. Especially, the introduced SHG can firstly increase the loss difference between the lasing and non-lasing modes so that the dual-mode or multi-mode coupling in the achieved SRO can be effectively eliminated and the stable SLM operation is achieved. At the same time, the SHG will automatically adjust the output coupling efficiency of SRO, so as to achieve efficient conversion efficiency and auto-pump depletion of SRO. In addition, due to the SHG, it is easy to achieve the low-intensity noise multi-wavelength output for the stable SLM SRO. As a result, the output powers of the SLM 1550 nm and 775 nm are up to 4.05 W and 3.25 W, respectively, and the total optical conversion of the built SRO can achieve 45.58%. The presented method paves a way to develop a compact stable SLM multi-wavelength SRO, and the obtained SRO is further beneficial to develop compact continuous-variable non-classical light fields.

We present a continuously tunable high-power continuous wave (CW) single-frequency (SF) Nd : YAlO3/lithium triborate (Nd:YAP/LBO) laser with dual-wavelength output, which is implemented by combining an optimized and locked etalon with an intracavity nonlinear loss. The obtained output powers of the stable SF 1080 and 540 nm lasers are 2.39 and 4.18 W, respectively. After the etalon is locked to an oscilating mode of the laser, the wideband continuous frequency tuning and long-term stable single-longitudinal-mode operation of the laser are successfully realized, which can be well used for the applications of quantum information and quantum computation. To the best of our knowledge, this is the first realization of the continuously tunable high-power CW SF 1080/540 nm dual-wavelength laser.

The high power all-solid-state continuous wave single-frequency laser is a significant source for science and application due to good beam quality and low noise. However, the output power of the laser is usually restricted by the harmful thermal lens effect of the solid gain medium. To address this issue, we develop a self-mode-matching compact all-solid-state laser with a symmetrical ring resonator in which four end-pumped Nd:YVO4 laser crystals are used for both laser gain media and mode-matching elements. With this ingenious design, the thermal lens effect of every laser crystal can be controlled and the dynamic of the designed laser including the stability range and the beam waist sizes at crystals can be manipulated only by adjusting the pump power used on each laser gain medium. Under an appropriate combination of pump powers on four crystals, self-mode-matching in a resonator is realized. A stable CW single-frequency at 1064 nm with 140-W power, 102-kHz linewidth, and low intensity noise is obtained. The presented design paves an effective way to further scale-up the output power of a compact laser by employing more pieces of gain media.

We report a method of optimizing the nonlinear crystal length of the intracavity frequency-doubling laser, which is achieved by maximizing the output power of the frequency-doubling laser in the case of ensuring the single longitudinal mode (SLM) operation of the laser. The optimal length of the nonlinear crystal for an SLM oscillation of the intracavity frequency-doubling laser is firstly theoretically predicted by comparing the losses introduced by the nonlinear crystal with different lengths with that of ensuring the SLM operation of the laser. Then three nonlinear LiB3O5 (LBO) crystals with the length of 18, 20, and 22 mm are adopted to be the frequency-doubling components in the experiment. By recording the output power and monitoring the longitudinal mode structure of the laser, it is found that the nonlinear LBO crystal with the length of 20 mm is the best candidate, since the output power is higher than that of the LBO crystal with the length of 18 mm, and the SLM operation of the laser is readily achieved compared to that of the LBO crystal with the length of 22 mm. The experimental results well agree with the theoretical predictions. The current method can pave a good way to attain a single-frequency continuous-wave intracavity frequency-doubling laser.

Objective Due to its small construction, low-intensity noise, and narrow linewidth, all-solid-state continuous-wave (CW) single-frequency lasers have been widely employed in scientific research, military, and medical applications. The emission wavelengths of lasers can be confined to many particular ranges due to the constraints of the fluorescence spectra of laser crystals, which cannot match the demands of rapidly increasing scientific research. As an effective laser wavelength conversion technology, the nonlinear frequency conversion process including optical parametric oscillation (OPO), sum frequency (SF), different frequency (DF), etc., provides multi-watt CW output powers in the deep ultraviolet (DUV) to mid-infrared and further expands the applied field of lasers. The single-frequency 1550 nm laser is frequently utilized in the formation of quantum squeezed and entangled states because its wavelength matches the low dispersion and low loss window of fibers, allowing for long-distance and steady laser transmission through the fiber. At present, there are several methods to generate a 1550 nm laser. Firstly, the 1550 nm laser is produced by a laser crystal co-doped with ytterbium-erbium (Yb3+, Er3+) directly pumped by a 976 nm semiconductor laser. The low cost, small construction, and ease of downsizing draw a lot of interest, however, the gain crystal's intrinsic excited state absorption restricts the laser output power. Secondly, the 1550 nm laser is also produced by an erbium (Er3+)-doped fiber laser. The erbium-doped fiber laser' s waveguide structure is advantageous for achieving high-power output, although the output laser's noise is rather high. In comparison to the previous approaches, the OPO process combines the benefits of low noise, small line width, and high stability to make the single-frequency 1550 nm laser the ideal contender. Especially, when we would like to generate the 1550 nm squeezed and entangled states, it is needed to use 775 nm and 1550 nm lasers as the pump and signal lasers of the optical parametric amplifier (OPA), respectively. As a result, an intra-cavity frequency-doubled (FD) singly resonant optical parametric oscillator (SRO) made of four mirrors is created and reported in this research, with simultaneous watt-level CW single-frequency lasers at 775 nm, 1550 nm, and 3393 nm. Methods In the experiment, to achieve high power signal laser and its frequency-doubled laser, it is important to acquire two focus waists in the cavity. The thermal lens effect of the MgO: PPLN crystal induced by the pump, signal, and idler lasers was initially estimated for this purpose. The thermal lens effect of MgO:PPLN is mostly due to its absorption of high-power intra-cavity signal lasers, according to theoretical simulations. On this basis, a ring resonator including two small waists was designed and built, which consists of four concave mirrors (radius of curvature of mirrors M1 and M2 is 60 mm and that of mirrors M3 and M3 is 40 mm), and whose whole length was optimized to 406 mm. The waist radii of the signal lasers at the OPO and second harmonic generation (SHG) crystals were 70 mu m and 52 mu m, respectively, in this scenario. To ensure a singly resonant optical parametric oscillator for the signal and single-pass transmission for the pump and idler lasers, the input coupler M1 was coated with high reflection (HR, reflectivity R>99. 8 %) film for the signal laser across 1400-1700 nm and high transmitting (HT, transmittivity T>97 %) film for the pump 1064 nm laser. Mirror M2 was coated with HR (R> 99. 8%) film for the signal laser and HT (T> 95%) film for the idler laser (3000-4200 nm). Mirror M3 was coated with HR (R > 99. 8%) film for the signal laser. Mirror M4 was coated with 1% transmission film for signal laser and HT (T>95%) film for frequency-doubled laser across 730-850 nm. The pump source was a handmade all-solid-state CW single-frequency 1064 nm laser with good performance. A coupling system consisting of an optical isolator (01), two half wave-plates (HWP), and two lenses oriented and focused the output laser beam on the OPO. A 40 mm long 5% MgO-doped periodically poled PPLN crystal (polarization cycle A = 30.49 mu m) was used as the OPO crystal owing to its wide transparent window and low absorption loss, which was placed at the focus point between the mirrors M1 and M2 to generate the high efficiency and high-power signal and idler lasers. For the intra-cavity SHG crystal, a PPKTP crystal (A = 24. 7 mu m) with the size of 2 mm x 2 mm x 15 mm was used and placed at the other waist between mirrors M3 and M4. For signal and frequency-doubled lasers, both sides of the crystals were covered with antireflection coatings. Both crystals were kept in separate ovens, each controlled by a 0.01 degrees C high precision temperature controller. The high-quality watts single-frequency infrared to mid-infrared laser output was generated by controlling the temperature of MgO: PPLN and PPKTP to 51 degrees C and 40.2 degrees C, respectively. Results and Discussions Using a small double waists single resonance oscillation and periodically polarized crystal, a single-frequency CW three-wavelength laser output from the near-infrared to the mid-infrared at the watt level was obtained. Figure 1 depicts the effect of the pump, signal, and idler lasers on the thermal lens focal length of MgO: PPLN crystal. It is shown that the effect of signal laser on the thermal lens focal length of MgO: PPLN crystal is much larger than that of idle and pump lasers. A compact four-mirror ring SRO was designed as Fig. 2. We obtained 4.1 W of 1550 nm signal laser output power and 2. 1 W of 3393 nm idler laser output power when the input pump power was 21 W (Fig. 4), the quantity factor M2 of 1550 nm laser was better than 1.05 (Fig. 5). The measured output power of signal and SHG lasers vs the input pump power is shown in Fig. 7. The pump threshold was discovered to be 8.3 W. When the incident pump power was raised to 16 W, more nonlinear effects appeared in the crystal as the signal laser power in the cavity rose, resulting in a reduction in FD conversion efficiency. When the pump power was increased to 21 W, the laser was operating stable and the output powers of 1550, 775, and 3393 nm lasers were 2.1, 1.1, and 1.7 W, respectively. The root-mean-square (RMS) variations of the output power during 5 h are less than 2.5% for the 1550 nm laser, 0.8% for the 3393 nm laser, and 1. 6% for the 775 nm laser, respectively (Fig. 8). The overall efficiency of light-to-light conversion was 23.3%. The 775 nm lasers' measured beam quality was better than 1. 13. (Fig. 10). The output laser operates in a single longitudinal mode. Conclusions The experimental findings of the creation of near-infrared to mid-infrared lasers employing an SRO made up of four-mirror ring resonators and period poled crystals were described in this study. To begin, we looked at OPO' s focusing characteristics as well as the impact of the nonlinear crystal' s thermal lens effect on the laser stable area and waist size. On this basis, a four-mirror ring resonator structure with double small waists was designed. Then, as the OPO and frequency-doubling crystals, a MgO: PPLN and a PPKTP were used to create the signal and frequency-doubled lasers, as well as the idler laser. When the pump power was 21 W, the output power of the 1550 nm signal laser could reach up to 2.1 W. The output powers of the 775 nm frequency-doubled laser and 3393 nm idler lasers were 1. 1 W and 1. 7 W, respectively, at the same time. The pump threshold was 8. 3 W, the overall light-to-light conversion efficiency was 23.3 %, and the beam quality was greater than 1.05 and 1.13 at 1550 and 775 nm, respectively. The RMS fluctuations of the power during 5 h were less than 2. 5% of 1550 nm, 0. 8 % of 3393 nm, and 1. 6% of 775 nm. The 775 nm and 1550 nm lasers created can be utilized as the pump and seed lasers of OPO and OPA, respectively, in quantum experiments to generate a 1550 nm compressed light field. It gives a trustworthy assurance for the development of a multi-component quantum light source, and it is viewed as a novel technological technique of attaining compact quantum squeezed state laser source manufacture.

Multi-beam laser processing is a very popular method to improve processing efficiency. For this purpose, a compact and stable multi-beam pulsed 355 nm ultraviolet (UV) laser based on a micro-lens array (MLA) is presented in this Letter. It is worth noting that the MLA is employed to act as the spatial splitter as well as the coupling lens. With assistance of the MLA, the 1064 nm laser and 532 nm laser are divided into four sub-beams and focused at different areas of the third-harmonic generation (THG) crystal. As a result, the multi-beam pulsed 355 nm UV laser is successfully generated inside the THG crystal. The measured pulse widths of four sub-beams are shorter than 9 ns. Especially, the generated four sub-beams have good long-term power stability benefitting from the employed MLA. We believe that the generated stable multi-beam 355 nm UV laser can meet the requirement of high-efficiency laser processing, and the presented method can also pave the way to generate stable and long-lived multi-beam UV lasers.

We present a continuously tunable single-frequency continuous wave (CW) Ti:Sapphire (Ti:S) laser with modulation-free-locked intracavity lithium niobate (LiNbO3) birefringent etalon (BE), which is implemented by detecting the polarization state variation of the reflected laser beam from the BE. After the BE is stably locked, the continuous frequency-scanning range up to 40 GHz is obtained within the tuning range of 300 nm while the resonator length of the Ti:S laser is continuously scanned. Because the modulation signal is unnecessary in the presented Ti:S laser system, the influences of the extra modulation signal on the intensity noise as well as the frequency noise of the laser are thoroughly eliminated and the modulation-noise-free continuously tunable single-frequency CW Ti:S laser is successfully attained.

The performance improvement of an all-solid-state single-frequency continuous-wave (CW) laser with high output power is presented in this paper, which is implemented by employing a temperature control system based on machine learning to control the temperature of laser elements including gain crystal, laser diode and so on. Because the developed temperature controller based on machine learning combines the back propagation (BP) neural network algorithm with the proportion-integration-differentiation (PID) control algorithm, the parameters of the PID are adaptive with the variation of the environment. As a result, the control speeds and control abilities of the temperatures of the elements are dramatically enhanced. In this case, the output characteristic and the adaptability to the environment as well as the stability of the single-frequency CW laser are also improved greatly.