This paper proposes a Nd-doped mode-locked fiber laser based on the nonlinear polarization rotation (NPR) effect, achieving stable laser output in the 0.9 µm band. The experiment adopts a double-end pumping structure and utilizes reflective grating pairs to compensate for dispersion and suppress competition at the 1.06 µm band. At a pump power of 358 mW, the output laser exhibits a central wavelength of 906.56 nm, a 3 dB bandwidth of 2.18 nm, a pulse width of 0.69 ps, and a signal-to-noise ratio exceeding 74 dB.

Terahertz (THz) frequency upconversion detection technology is an important subject in the field of THz measurement. It offers several advantages, including the capability for room-temperature operation, fast response, high sensitivity, and high dynamic range.The nonlinear inorganic crystals suitable for THz frequency upconversion detection include MgO:LiNbO3 (LN) , KTiOPO4 (KTP) , KTiOAsO4 (KTA) , and RbTiOPO4 (RTP) . The spectral range of the THz parametric source based on LN crystal can be 0.7 similar to 2.9 THz, while in the frequency range from 3.0 to 6.5 THz, KTP, KTA, and RTP crystals must be used in combination to achieve essential coverage. Currently, the characteristics of the THz frequency upconversion detection based on LN and KTP crystals have been reported. In this paper, the THz wave frequency upconversion detection characteristics based on RTP crystal are studied. The experimental setup of the THz parametric upconversion detection based on RTP crystal was mainly composed of three parts the pump source, the THz parametric generator, and the THz frequency upconversion detection part. The pumping source was a 1 064.1 nm Q-switched laser with a pulse width of 420 ps and a pulse repetition rate of 1 Hz. Two identical RTP crystals were used in the experiment. One crystal was used as the THz generator to generate THz waves, the other was used to realize frequency upconversion detection. The physical base of THz wave generation and frequency upconversion detection based on RTP crystal is Stimulated Polariton Scattering (SPS). The necessary condition for SPS is the existence of transverse A1 modes which are both infrared and Raman active in the crystal. The THz wave generation in RTP crystal was caused by the stimulated scattering of the polaritons associated with the most intensive transverse A1 mode of 271 cm(-1). But the existing of many much weaker transverse A1 modes of 211 cm(-1), 170 cm(-1), 161 cm(-1), 145 cm(-1), 107 cm(-1), 83 cm(-1), 51 cm(-1) made the Stokes and terahertz waves intermittently tunable. So the generated THz waves were mainly in four discrete wavelength regions, which were from 3.01 to 3.09 THz, from 3.53 to 4.17 THz, from 4.54 to 4.66 THz, and from 5.35 to 5.89 THz. The THz waves with center frequencies of 3.84 THz and 5.58 THz were selected for measurement in this study. In the SPS process, the pumping, Stokes, and terahertz waves must obey the energy conservation law and momentum conservation law. Because the refractive indexes of RTP crystal in the terahertz range are very large, only noncollinear phase matching can be realized. The angle between the pumping and Stokes beams (expressed as theta) and the angle between the pumping and THz beams (expressed as beta) are dependent on the THz frequency. theta is very small, usually between a few tenths of a degree and a few degrees. However, beta is rather large, distributed around 58 degrees. The shape of the RTP crystal in the X-Y plane was designed as isosceles trapezoid with a base angle of 58 degrees, a baseline length of 18.0 mm, and a waist length of 11.8 mm. The thickness in the Z direction was 5.0 mm. Two waist surfaces were both AR coated in the range of 1 060 similar to 1 100 nm. When the crystal was used as the THz generator, the pump light was vertically incident from one waist of the isosceles trapezoid, reflected by the bottom side, and left the crystal from the other waist. It was because of the design of the isosceles trapezoid with a base angle of 58 degrees that the generated terahertz wave could be output almost vertically from the bottom side. The THz wave was focused and injected into the second RTP crystal through two off-axis parabolic mirrors (OAP1 and OAP2). The THz energy was attenuated by adding black polyethylene terephthalate (PET) plates between OAP1 and OAP2. A vertical slit was set in the THz optical path between the two parabolic mirrors, and the specific center frequency and bandwidth of the injected THz wave were selected by adjusting the transverse position and width of the slit, respectively. The upconverted signal spectral composition and intensity were detected by an optical spectrum analyzer and a highly sensitive photodiode, respectively. The upconverted signal pulse energy (expressed as the equivalent voltage displayed on the oscilloscope) showed a good linear relationship with the input THz pulse energy. The minimum detectable energy achieved at 3.84 THz was 2.29 fJ and the dynamic range was 52.7 dB. The minimum detectable energy obtained at 5.58 THz was 0.311 fJ and the dynamic range was 56.3 dB. The interaction length within the RTP crystal for the pump light, THz wave, and upconverted Stokes signal did not exceed 15 mm. The minimum detectable pulse peak power obtained from the RTP-based THz frequency upconversion detection system was comparable to that of the KTP-based system, while the interaction length for the pump light, THz wave, and upconverted Stokes signal in KTP crystal was larger than 90 mm. Regarding the frequency coverage of inorganic crystal frequency upconversion detection systems, the tuning range of a single crystal is discontinuous, the combination uses of RTP, KTP and KTA crystals can cover the spectral range from 3.0 to 6.5 THz.

Lasers with a wavelength of 0.9 mu m have important applications in the medical, printing, detection, military, and biological fields. We have developed an Nd-doped fiber laser that achieved the observation of the conventional soliton at 0.9 mu m waveband for the first time. A pair of transmissive diffraction gratings was employed to introduce negative dispersion and suppress mode competition at 1.06 mu m, which resulted in a suppression ratio of up to 41.9 dB. A maximum repetition rate of 13.14 MHz is observed, with a pulse width ascertained at 3.92 ps. To our knowledge, this is the first instance that conventional solitons have been obtained through dispersion management in a 0.9 mu m Nd-doped fiber laser. This work offers a novel approach for achieving shorter pulses in Nd-doped fiber lasers.

This paper investigated the characteristics of the phonon-assisted Raman generation in KGd(WO4)2 crystal pumped by short -band-width Q-switched pulses. The KGd(WO4)2 Raman laser pumped by 1064.15 nm pulse generates a phonon wave in the KGd(WO4)2 crystal besides the ordinary Stokes laser output at 1177.19 nm. A synchronous weak pumping laser beam at 1273.38 nm generates its Stokes laser at 1438.51 nm with the help of the generated phonon wave in the Raman crystal. For a given pumping pulse energy of 45.0 mJ at 1064.15 nm, corresponding to the pumping pulse energy at 1273.38 nm increasing from 0.89 mJ to 1.26 mJ, the obtained Stokes pulse energy at 1438.51 nm increases from 48.0 µJ to 59.8 µJ. For a given pumping pulse energy of 1.03 mJ at 1273.38 nm, corresponding to the pumping pulse energy at 1064.15 nm increasing from 40.4 mJ to 59.0 mJ, the obtained Stokes pulse energy at 1438.51 nm increases from 25.0 µJ to 122.4 µJ. The maximum pulse energy at 1438.51 nm is 125 µJ when the 1064.15 nm pump pulse energy is 55.0 mJ and the 1273.38 nm pump pulse energy is 1.26 mJ, respectively. An expression for the phonon-assisted Raman pulse intensity is derived. The simulation results are consistent with the experimental results on the whole.

Terahertz (THz) frequency upconversion detection is a promising method in the field of THz measurement. This paper focuses on the dependence of the THz frequency upconversion detection characteristics based on the stimulated polariton scattering (SPS) effect in lithium niobite (LN) crystal on the pumping pulse energy. It was found that optimal pumping pulse energy exists, which leads to the largest ratio of the upconverted Stokes signal to the background clutter. In the theoretical part, the background clutter is divided into two parts: the amplified spontaneous Stokes fluorescence and other background clutter. The expressions for the upconverted Stokes signal and amplified spontaneous Stokes fluorescence are derived, and the terahertz wave frequency upconversion detection characteristics varying with the pumping pulse energy are successfully explained.

This paper demonstrates the characteristics of the THz parametric frequency upconversion detection based on the stimulated polariton scattering in KTiOAsO4 (KTA) crystal pumped by a 1064 nm pulsed laser (420 ps, 1 Hz). The detectable spectral ranges can be from 3.54 to 4.03 THz, from 4.08 to 4.50 THz, from 4.71 to 5.16 THz, and from 5.87 to 6.32 THz. The minimum detectable energy is 0.24 fJ at 4.92 THz with a dynamic range of 57 dB.

Slitless spectroscopy eliminates the need for slits, allowing light to pass directly through a prism or grism to generate a spectral dispersion image that encompasses all celestial objects within a specified area. This technique enables highly efficient spectral acquisition. However, when processing China Space Station Telescope (CSST) slitless spectroscopy data, the unique design of its focal plane introduces a challenge: photometric and slitless spectroscopic images do not have a one-to-one correspondence. As a result, it becomes essential to first identify and count the sources in the slitless spectroscopic images before extracting spectra. To address this challenge, we employed the You Only Look Once object detection algorithm to develop a model for detecting targets in slitless spectroscopy images. This model was trained on 1560 simulated CSST slitless spectroscopic images. These simulations were generated from the CSST Cycle 6 and Cycle 9 main survey data products, representing the Galactic and nearby galaxy regions and the high galactic latitude regions, respectively. On the validation set, the model achieved a precision of 88.6% and recall of 90.4% for spectral lines, and 87.0% and 80.8% for zeroth-order images. In testing, it maintained a detection rate >80% for targets brighter than 21 mag (medium-density regions) and 20 mag (low-density regions) in the Galactic and nearby galaxies regions, and >70% for targets brighter than 18 mag in high galactic latitude regions.

Highly sensitive terahertz frequency upconversion detection was demonstrated with a RbTiOPO4 crystal. The detectable THz frequency ranges were 3.6-4.0, and 5.4-5.7 THz. The minimum detectable terahertz energy at 5.6 THz was about 0.2 fJ.

Multi-pulse dynamic patterns have been experimentally documented in a passively mode-locked (PML) erbium-doped fiber (EDF) laser using an Sb2S3-PVA saturable absorber (SA). The fundamental mode-locking operation, with a repetition rate of ∼3.22 MHz, a pulse width of ∼2.5 ps, a signal-to-noise ratio (SNR) of ∼50 dB and a peak power over 200 W, was achieved under a pump power from 280 to 360 mW with appropriate polarization states introduced by the polarization controllers (PCs). By rotating the orientation of the intra-cavity PCs carefully and slowly at a pump power of 350 mW, it was found that a multi-pulse bunch was transformed gradually from a single-pulse to a twelve-pulse bunch, with several intermediate transition states of multi-pulse bunches being observed. In addition, other characteristic modes including disordered multi-pulses and soliton rains have been experimentally observed by meticulously adjusting the polarization states of PCs at a pump power of 350 mW. Our systematic study clearly demonstrates that Sb2S3has potential as an effective SA for generating different operation states of multi-pulses in PML anomalous-dispersion EDF lasers.

The evolution of multiple pulses and the pump hysteresis phenomenon were observed in a passively mode-locked Er-doped fiber laser using an Sb2S3-PVA saturable absorber. As the pump power was increased, the generations of onefold, twofold and threefold pulses were meticulously documented. When the pump power was decreased, the evolution of fivefold and sixfold pulses was carefully recorded, accompanied by a clear pump hysteresis phenomenon. A thorough analysis was conducted to examine and reveal the inversely proportional relationship between the RF spectrum modulation periods and the total pulse intervals of the multi-pulse bunches including from onefold to sixfold pulses.

A late-model all-fiber mode-locked laser was introduced in this paper. This pulsed Er-doped fiber laser has a novel Sagnac loop structure and uses the tapered fiber coated with two-dimensional layer ferromagnetic insulator Cr2Si2Te6 as a saturable absorber in order to achieve passive mode locking. When the pump power was 167.6 mW, the laser worked at the fundamental repetition frequency of 19.1 MHz with a signal-to-noise ratio of 62.5 dB. The central wavelength of the spectrum was 1561.0 nm, and the maximum output power was 8.9 mW with a minimum pulse width of 5.2 ps. The mutual interference of beams makes the use of the saturable absorber more efficient. The results reveal that this Er-doped fiber laser has great application potential in nonlinear optics and ultrafast photonics.

In this work, a Cr2Si2Te6-based tapered fiber saturable absorber with a modulation depth of 4.7 % and a saturable intensity of 28.67 MW/cm2 was fabricated by liquid-phase exfoliation. A triple-wavelength erbium-doped mode-locked fiber laser with a Sagnac loop structure was successfully generated. Its output wavelengths were 1560.2, 1561.3, and 1562.8 nm. The basic repetition rate was 0.97 MHz, corresponding to a signal-to-noise ratio of 49 dB. This is the first demonstration of a triple-wavelength mode-locked fiber laser focusing on a two-dimensional ferromagnetic insulator Cr2Si2Te6. This experiment shows that this triple-wavelength mode-locked fiber laser has excellent performance.

Based on the Nd-doped single-mode fiber as the gain medium, an all-fiber 12th harmonic mode-locked (HML) laser operating at the 0.9 mu m waveband was obtained for the first time, to the best of our knowledge. A mandrel with a diameter of 10 mm was employed to introduce bending losses to suppress mode competition at 1.06 mu m, which resulted in a suppression ratio of up to 54 dB. The 1st-12th order HML pulses with the tunable repetition rate of 494.62 kHz-5.94 MHz were obtained in the mode-locked laser with a center wavelength of similar to 904 nm. In addition, the laser has an extremely low threshold pump power of 88 mW. To the best of our knowledge, this is the first time that an HML pulse has been achieved in a 0.9 mu m Nd-doped single-mode all-fiber mode-locked laser with the advantages of low cost, simple structure, and compactness, which could be an ideal light source for two-photon microscopy.

太赫兹参量源是一种激光驱动的太赫兹辐射源,它具有高相干性、可调谐、室温运转等优点.在简要介绍太赫兹参量源的基本原理后,重点总结了近年来国内外对太赫兹参量源的代表性研究成果,主要包括:1)太赫兹参量源中常用的几种非线性晶体,包括铌酸锂、磷酸钛氧钾、砷酸钛氧钾、磷酸钛氧铷;2)大单脉冲能量太赫兹参量源,主要产生方法包括使用垂直表面出射结构、使用环形腔、增加非线性晶体损伤阈值等,目前报道的最大单脉冲能量达到17μJ;3)高平均功率太赫兹参量源,主要产生方法包括使用半导体激光器侧面泵浦激光器、兼顾提高泵浦光脉冲能量和脉冲重复频率等,目前报道的最大平均功率为367 μW;4)太赫兹参量源的理论模拟,主要包括以耦合波方程为基础的,分别针对太赫兹参量产生器、种子注入式太赫兹参量产生器、内腔泵浦与外腔泵浦太赫兹参量振荡器建立的理论模型.

Dissipative solitons are generalized solitons with much larger pulse energy and width than conventional solitons, and the pulse characteristics will be changed dramatically during transmission. Nonlinear photonic absorption device in nonlinear optical resonator can provide saturable absorption effect to generate ultrashort pulses. However, most of the nonlinear photonics devices are based on inorganic materials such as two-dimensional materials with complex production process, and there are relatively few such researches on organics. In this paper, nonlinear photonics absorption device based on hydrazone organics with high molecular polarizability and significant third-order optical nonlinearity generate ultrashort pulses. The dissipative soliton pulses are obtained by controlling the dispersion, and the pulses are compressed to the near-transformation limit of 408 fs with a compression ratio of 44.6. More importantly, the extra-cavity transport properties of dissipative solitons are discussed. Dissipative noise-like soliton pulses are discovered after additional anomalous dispersion fiber, further demonstrating that the physical laws and optical properties of dissipative solitons are completely different from those of traditional optical pulses. We expect that these experimental advances can provide some experimental basis and support for the propagation of dissipative solitons.

The interaction of 2D materials with ultrashort laser excitation generates fiber soliton pulses with extreme nonlinear absorption characteristics, which are essential for generating ultrafast pulses. However, searching for suitable nanomaterials to achieve versatile photonic properties is difficult. Factors such as cost, manufacturing process complexity, optical response time, and nonlinear absorption effects make the balance between high performance and low cost a constant challenge, greatly hindering the research and development of ultrafast photonics technology. For fiber soliton pulse systems, γ‐MnO 2 , as a transition metal oxide (TMO), shows excellent potential among many candidate nanomaterials due to its rich narrow‐band optoelectronic microstructural features and nonlinear optical properties. In this work, this fundamental trade‐off is overcome and γ‐MnO 2 is investigated as a nonlinear optical material for multifunctional fiber soliton pulsed lasers. The outputs of conventional soliton pulses, 23rd order harmonic soliton‐molecule picosecond pulses, continuous and soliton pulse waves coexist in dual‐wavelength, and soliton rain pulses are obtained simultaneously, successfully achieving a technological breakthrough in nanophotonics and pulse dynamics. It is demonstrated that MnO 2 has a broad application prospect for generating nonlinear effects such as fiber optic soliton pulses, which provides an effective and rich theoretical support for developing ultrafast photonics of narrow‐band optoelectronic materials.

As a novel material with narrow band gap and natural van der Waals heterostructures (vdWH), francketie has potential applications in the field of optoelectronic fields. However, few studies have applied its nonlinear optical absorption properties to ultrafast fiber lasers. Here, we synthesized francketie nanosheets via the liquid-phase exfoliation (LPE) method. By incorporating the polyvinyl alcohol (PVA), a franckeite-PVA saturable absorber (SA) was fabricated to achieve a mode-locked Yb-doped fiber laser (YDFL) for the first time to the best of our knowledge. The saturation intensity and modulation depth of the SA were measured about 75 MW∕cm2 and 7%, respectively. The proposed franckeite-based YDFL demonstrates stable mode-locked operation with the maximum single energy of 5.35 nJ and the pulse duration of 1.57 ns. Our experimental results fully prove that franckeite may have wide potential for designing ultrafast photonics devices with low cost, high stability and excellent performance.

Macro-bending of optical fiber makes bending loss increase at longer wavelength, so the 1.06 mu m laser can be suppressed without affecting 0.9 mu m laser emission. In this paper, it is implemented as a new approach to suppress 1.06 mu m laser emission and produce 0.9 mu m laser in an Nd-doped single-mode all-fiber mode-locked laser. Dissipative soliton resonance (DSR) pulses with pulse width increasing from 1.46 ns to 6.33 ns are generated in the Nd-doped all-fiber mode-locked laser operating at 0.9 mu m. Besides that, the 0.9 mu m pulse burst with pulse number of 1-3 is generated.

Pulse bursts are generated in an Yb-doped all-normal dispersion (ANDi) passively mode-locked fiber laser with Raman scatting based on nonlinear polarization rotation (NPR). The number of pulses can be continuously adjusted from 1 to 8 by adjusting the pump power. The output power varies stepwise with linearly increasing of input power and pulse numbers in the bursts. We explain that the pulse bursts in ANDi fiber laser are formed by the clamping of pulse width and peak power. The energy evolution of the pulses burst with Raman component is experimentally realized in Yb-doped fiber laser, which is excepted to benefit energy controlling in applications such as laser material ablation and so on.

In our work, a new-type, to the best of our knowledge, ferromagnetic insulator and its nonlinear optical absorption characteristics and related ultrafast modulation applications were investigated. Cr2Si2Te6 saturable absorbers (SAs) with a modulation depth and a saturable intensity of 9.7% and 3.5MW/cm2 were fabricated. By adjusting the pump power to 120 mW and optimizing the polarization state, traditional soliton operations were obtained successfully; the corresponding duration of pulse and the fundamental repetition rate were ∼1.33ps and 6.70 MHz, and the signal-to-noise ratio was 50 dB. The experimental results reveal that Cr2Si2Te6 with excellent saturable absorption characteristics can be used as a SA to obtain ultrafast pulse lasers.