Highly efficient Cherenkov radiation generation in the irregular point of hollow-core photonic crystal fiber

Highly efficient Cherenkov radiation(CR) is generated by the soliton self-frequency shift(SSFS) in the irregular point of a hollow-core photonic crystal fiber(HC-PCF) in our laboratory.The impacts of pump power and wavelength on the CR are investigated,and the corresponding nonlinear processes are discussed.When the average power of the 120 fs pump pulse increases from 500 mW to 700 mW,the Raman soliton shifts from 2210 nm to 2360 nm,the output power of the CR increases by 2.3 times,the maximum output power ratio of the CR at 539 nm to that of the residual pump is calculated to be 24.32:1,the width of the output optical spectrum at the visible wavelength broadens from 35 nm to 62 nm,and the conversion efficiency η of the CR in the experiment can be above 32%.     

Polarization-dependent two-color dispersion wave generation and evolution in polarization-maintaining photonic crystal fiber

We investigate the effect of the polarization state of the input pulses on the visible emissions in the anomalous dispersion region of polarization-maintaining photonic crystal fiber (PM-PCF), by using ～100 fs pump pulses whose central wavelength (1064 nm) is close to the second zero dispersion wavelength (1100 nm) of the fiber, where the soliton fission mechanisms play an important role. The experimental results show that the phase-matching two-color dispersive wave emission, one at 582 nm and the other at 600 nm, is polarization-dependent and frequency shift results from the different dispersion characteristics along the two orthogonal principal axes of PM-PCF. Furthermore, it is observed for the first time that the variation of the linear input polarization angles in 45° region almost has no influence on the output spectral profiles, and the break variation of the output spectrum exists when the angle between the polarization of the linear incident pulse and the fast-axis or the slow-axis of PM-PCF is 45°, which are attributed to the coupling between the two polarization modes in high birefringent PM-PCF.     

Broadband tunable Raman soliton self-frequency shift to mid-infrared band in a highly birefringent microstructure fiber

Raman soliton self-frequency shifted to mid-infrared band(λ 2 μm) has been achieved in an air-silica microstructure fiber(MF). The MF used in our experiment has an elliptical core with diameters of 1.08 and 2.48 μm for fast and slow axis. Numerical simulation shows that each fundamental orthogonal polarization mode has two wide-spaced λZDW and theλZDW pairs located at 701/2110 nm and 755/2498 nm along the fast and slow axis, respectively. Using 810-nm Ti:sapphire femtosecond laser as pump, when the output power varies from 0.3 to 0.5 W, the furthest red-shift Raman solitons in both fast and slow axis shift from near-infrared band to mid-infrared band, reaching as far as 2030 and 2261 nm. Also, midinfrared Raman solitons can always be generated for pump wavelength longer than 790 nm if output pump power reaches0.5 W. Specifically, with pump power at 0.5 W, the mid-infrared soliton in slow axis shifts from 2001 to 2261 nm when the pump changes from 790 nm to 810 nm. This means only a 20 nm change of pump results in 260 nm tunability of a mid-infrared soliton.     

在BBO中获得230.8—223.2nm高功率和频输出

用Q-YAG泵浦的Rh·6G染料激光在一块45°切割的β-BaB₂O₄(BBO)晶体中倍频,产生294.8—282.5nm范围的连续调谐输出,其能量为8mJ(在285nm处)。用这个倍频光与泵浦染料后剩余基波(1064nm)在另一块45°切割的BBO中和频,已获得230.8—223.2nm范围的连续调谐输出,其能量为120μJ,相应的峰值功率为12kW。还简述了获得高功率和频输出的关键技术。     

Several hundred kHz repetition rate nanosecond pulses amplification in Er–Yb co-doped fiber amplifier

We have experimentally investigated several hundred kHz repetition rate 1,550-nm nanosecond pulses amplification in Er–Yb co-doped fiber amplifier (EYDFA). The experimental setup has three stage fiber amplifiers. At the output of the second stage EYDFA, Yb³⁺ ions induced amplified spontaneous emission (Yb-ASE) is not observed owing to the low pump power. In the third stage EYDFA, a simultaneously seeded 1,064-nm continuous-wave laser is used to control Yb-ASE. Without any additional 1,064-nm signal, significantly backward Yb-ASE which caused loss-induced heat accumulation at the input port of the pump combiner can be observed. The monitored temperature at the input port of the pump combiner rapidly grows from 30 to 80 °C when the pump power is turned from 20 to 32 W. When a 196-mW forward 1,064-nm laser is added, the monitored backward Yb-ASE power is significantly declined, and the monitored temperature is kept below 35 °C. But, the additional signal caused a large power fraction at 1,064 nm in the output laser. In our experiment at the maximum pump power of 48.5 W, the total output power is 20 W with ~6.4-W 1,550-nm pulsed laser and ~13-W 1,064-nm continuous-wave laser.     

LD end-pumped c-Cut Nd:YVO<Subscript>4</Subscript>/KTP self-Raman laser at 560 nm

Intra-cavity sum frequency generation (SFG) of c-cut Nd:YVO₄ self-Raman laser was investigated for the first time. A 4 × 4 × 10 mm³ KTP crystal with a type-II phase-matching cutting angle (θ = 83.4°, φ = 0°) was used for SFG between the fundamental light at 1066 nm and first-Stokes light at 1178 nm. The laser system with different curvature radii of output couplers and different pulse repetition frequencies were investigated. At a pump power of 14 W and pulse repetition frequency of 20 kHz, the average output power of yellow-green laser at 560 nm up to 840 mW was achieved, corresponding to a slope efficiency of 7.6% and a conversion efficiency of 6% with respect to diode pump power.     

Observation of stable bound soliton with dual-wavelength in a passively mode-locked Er-doped fiber laser

A phase-locked bound state soliton with dual-wavelength is observed experimentally in a passively mode-locked Erdoped fiber(EDF) laser with a fiber loop mirror(FLM). The pulse duration of the soliton is 15 ps and the peak-to-peak separation is 125 ps. The repetition rate of the pulse sequence is 3.47 MHz. The output power is 11.8 mW at the pump power of 128 mW, corresponding to the pulse energy of 1.52 nJ. The FLM with a polarization controller can produce a comb spectrum, which acts as a filter. By adjusting the polarization controller or varying the pump power, the central wavelength of the comb spectrum can be tuned. When it combines with the reflective spectrum of the fiber Bragg grating, the total spectrum of the cavity can be cleaved into two parts, then the bound state soliton with dual-wavelength at 1549.7 nm and 1550.4 nm is obtained.     

Widely tunable PPLN/IOPO driven by a diode-end-pumped Q-switched Nd:YVO<Subscript>4</Subscript> laser

This paper reported a broadband tuning intracavity optical parametric oscillator (IOPO), based on the multiple grating periodical poled lithium niobate (PPLN) pumped by a acoustic-optical (AO) Q-switched Nd:YVO₄ laser. The widely tunable OPO output signal wavelength range from 1390 to 1605 nm, which was obtained by changing PPLN poling period from 27.8 to 31.6 μm at a certain temperature of 46°C, while the continuous tuning range was measured from 1475 to 1592 nm with the PPLN poling period of 30 μm by varying the temperature of nonlinear crystal PPLN from 50 to 120°C. The maximum output power of 0.92 W at 1534 nm with the minimum pulse width of 5.17 ns was generated under the incident pump power of 9.6 W at 808 nm. The corresponding peak power and single pulse energy were calculated to be 5.94 kW and 30.7 μJ, respectively. The M ₂-factor was measured to be 2.01 at the signal power of 0.4 W.     

孤子分子/类噪声脉冲可切换的混合锁模光纤激光器

不同类型脉冲之间的演化是被动锁模光纤激光器丰富动力学的体现。报道了一种可实现多种脉冲切换的混合锁模光纤激光器,当泵浦功率为400 mW时实现了孤子分子、谐波锁模、孤子簇之间的相互切换。增加泵浦功率至600 mW时获得了类噪声脉冲输出,对应的输出功率和单脉冲能量分别为15.2 mW和0.86 nJ。通过调节偏振控制器实现了类噪声脉冲中心波长从1 895 nm到1 930 nm可调谐。所搭建的激光器具有锁模脉冲可切换,波长可调谐,能自启动等优点。     

Study on broadly tunable optical parametric oscillator based on MgO-doped periodically poled LiNbO3 crystal

An efficient source of all-solid-state broadly tunable mid-infrared optical parametric oscillator based on a periodically poled MgO-doped lithium niobate is reported. The pump source is a 1064nm acousto-optically Q-switched diode-pumped Nd:YAG laser. A broadly tunable mid-infrared output from 1.56 to 1.67 μm were generated, with corresponding idler wavelengths of 3.34 to 2.93 μm by temperature tuning from 40 to 200°C. When the average pump power is 1.61 W with about 70 ns pulse duration operating at a repetition rate of 10 kHz, the maximum signal output power of the PPMgLN-OPO is about 211 mW at 1631 nm.     

2.7-W Ho<Superscript>3+</Superscript>-doped silica fibre laser pumped at 1100 nm and operating at 2.1 μm

The basic performance characteristics of a Ho ³⁺-doped silica fibre laser that operates in a single transverse mode at ~2.1 µm and is pumped with the 1100-nm output from a free-running Yb ³⁺-doped silica fibre laser are presented. We measure a maximum slope efficiency (with respect to launched pump power) of 35% and we generate a maximum output power of 2.7 W at an optical-to-optical efficiency of 18% with respect to the incident pump power. The wavelength of the output is length tuned from 2090 nm to 2100 nm when the a _absL product varies from 1.2 to 2.7. The use of the free-running output from a Yb ³⁺-doped silica fibre laser to pump the Ho ³⁺-doped silica fibre laser is very convenient and allows significant scaling of the output power.     

980 nm Yb-doped single-mode fiber laser and its frequency-doubling with BIBO

A quasi-three-level Yb-doped single-mode fiber laser at 980 nm by adopting two 0° fiber ends as cavity mirrors generated a total output power of 1.32 W with the slope efficiency of 75.3%. The fiber length was 36.5 cm close to the optimal theoretical fiber length. The corresponding optical conversion efficiency was 66% from the incident pump power at 946 nm to the laser power at 980 nm. Through frequency-doubling with BIBO crystal, a total output power of 15 mW at 490.8 nm was obtained.     

Supercontinuum generation in the irregular point of hollow-core photonic crystal fiber

Broadband supercontinuums (SC) are generated by soliton self-frequency shift (SSFS) of hollow-core photonic crystal fiber (HC-PCF) in our laboratory. With the pump works at 810 nm when the pump power increase from 400 to 600 mW, the Raman Soliton shifts from 2089 to 2215 nm, the bandwidth of SC increases from 2213 to 2320 nm. The ultra-violet part of SC is below 180 nm, and the mid-infrared part of SC exceeds 2500 nm. Moreover, the influence of pump power on SC is also analyzed.     

Widely and continuously tunable optical parametric generator infrared laser

The experimental results of a high efficiency infrared laser are demonstrated on a quasi phase matched optical parametric generator in PPMgLN (5% MgO doping) pumped by a 1064 nm Nd:YAG laser. A broad continuous signal spectrum 1.56?C1.67 ??m are obtained by tuning the crystal temperature from 20°C to 200°C. When the average pump power is 1.82 W with about 70 ns pulse duration operating at a repetition rate of 10 kHz, the maximum total output power of the PPMgLN OPG is about 323.58 mW consisting of 210 mW of 1.639 ??m signal radiation and 113.58 mW of 3.02 ??m idler radiation.     

2080 nm long-wavelength,high-power dissipative soliton resonance in a dumbbell-shaped thulium-doped fiber laser

We demonstrate a 2080 nm long-wavelength mode-locked thulium(Tm)-doped fiber laser operating in the dissipative soliton resonance(DSR) regime. The compact all-fiber dumbbell-shaped laser is simply constructed by a 50/50 fiber loop mirror(FLM), a 10/90 FLM, and a piece of large-gain Tm-doped double-clad fiber pumped by a 793 nm laser diode. The 10/90 FLM is not only used as an output mirror, but also acts as a periodical saturable absorber for initiating DSR mode locking. The stable DSR pulses are generated at the center wavelength as long as 2080.4 nm, and the pulse duration can be tunable from 780 to 3240 ps as the pump power is increased. The maximum average output power is 1.27 W, corresponding to a pulse energy of 290 nJ and a nearly constant peak power of 93 W. This is, to the best of our knowledge, the longest wavelength for DSR operation in a mode-locked fiber laser.     

Enhanced violet Cherenkov radiation generation in GeO2-doped photonic crystal fiber

We demonstrate the generation of highly efficient Cherenkov radiation (CR) in the fundamental mode of a GeO₂-doped two zero dispersion wavelengths photonic crystal fiber (PCF). Using a high power femtosecond Yb-doped PCF laser emitting 100 fs pulses as the pump source, CR with an efficiency of >40 % and a bandwidth of 38 nm is obtained in the visible-wavelength range when the average power of pump light is 1.27 W. It is that injecting the pump light in deep anomalous dispersion regime contributes to such an efficient spectrally isolated CR. The mechanism during the forming of CR is discussed and the experimental results are in good agreement with the calculation.     

高功率,红光至中红外可调谐腔内和频光学参量振荡器

本文利用高重复频率,高平均功率大模场面积飞秒光纤激光器作为同步抽运源,抽运以多周期极化掺氧化镁铌酸锂为非线性晶体的单共振光学参量振荡器,获得了高功率可调谐红光至中红外光,信号光调谐范围为1450—2200 nm,闲频光调谐范围为2250—4000 nm,在2 W的抽运功率下,信号光输出波长为1502 nm时获得最大输出功率374 mW,转换效率为18.7%,脉冲宽度为144 fs,此时中红外输出中心波长为3.4μm,平均功率为166 mW.再利用BBO晶体对信号光进行腔内和频,获得和频光输出波长调谐范围为610—668 nm,在4.1 W抽运的情况下,最高平均功率为615 nm处的694 mW,转换效率达16.9%.     

低阈值锁模状态可转换的全保偏光纤激光器

报道了一种可实现低阈值自启动的全保偏九字腔光纤激光器。谐振腔结构中使用相移器降低锁模阈值,当泵浦功率达到120 mW时,便可实现自启动的传统孤子锁模,中心波长为1530 nm,脉冲宽度为614.6 fs。随后泵浦功率逐渐增大到470 mW,实现了从孤子脉冲到类噪声脉冲的转换,在该锁模状态下的激光器输出功率为63.2 mW,对应的类噪声脉冲能量为5.69 nJ。所搭建的激光器具有低锁模阈值、自启动的优势,并且仅通过调节泵浦功率就能够实现超快脉冲和高能量脉冲间的转换,具有广泛的应用价值。     

A comparison of resonantly pumped Ho:YLF and Ho:LLF lasers in CW and Q-switched operation under identical pump conditions

Singly 0.5 at.% Ho doped crystals of YLiF₄ (YLF) and LuLiF₄ (LLF) are studied under identical pump conditions in continuous-wave (CW) and Q-switched operation. Longitudinal end-pumped CW laser performance shows Ho:LLF to have a slightly lower threshold and a slightly higher slope efficiency with respect to absorbed pump power than Ho:YLF. Both lasers were operated on π-polarization. At a cavity output coupling of 20% and a crystal length of 30 mm, the Ho:LLF (Ho:YLF) laser yielded 18.8 W (18 W) of CW output at a wavelength of 2067.8 nm (2064.0 nm) for 41.4 W (42.2 W) of absorbed pump power with a slope efficiency of 67.1% (65.6%) and an optical-to-optical efficiency of 45.4% (42.6%) with respect to absorbed pump power. With the same output coupling and a crystal length of 40 mm, the Ho:LLF (Ho:YLF) laser yielded 20.5 W (18.1 W) of CW output at a wavelength of 2067.7 nm (2064.3 nm) for 51.5 W (50.0 W) of absorbed pump power with a slope efficiency of 58.4% (55.4%) and an optical-to-optical efficiency of 39.8 (36.1%) with respect to absorbed pump power. The influence of the temperature of the cooling mount on CW laser performance was studied and showed very similar results for both laser materials. At full pump power, a slope of −155 mW/°C (−149 mW/°C) was observed for the Ho:LLF (Ho:YLF) laser with a crystal length of 30 mm. In Q-switched operation, the Ho:LLF (Ho:YLF) laser produced 37 mJ (38.5 mJ) at a repetition rate of 100 Hz with a pulse duration of 38 ns (35 ns) at a wavelength of 2053.1 nm (2050.2 nm) with a slope efficiency of 30.3% (31%) and an optical-to-optical efficiency of 14.2% (13.9%) with respect to absorbed pump power. The beam quality was nearly diffraction limited (M ²<1.1).     

Theoretical and experimental investigations of nanosecond 177.3 nm deep-ultraviolet light by second harmonic generation in KBBF

We have presented theoretical and experimental investigations of nanosecond (ns) deep-ultraviolet (DUV) 177.3 nm radiation by means of second harmonic generation (SHG) from a frequency-tripled Nd:YAG laser (355 nm, 49 ns and 10 kHz) in KBe₂BO₃F₂ (KBBF) nonlinear crystal for the first time. A DUV KBBF-SHG numerical model, accounting for linear absorption, pump depletion, beam spatial birefringent walk-off and diffraction, is performed in the Gaussian approximation of spatial and temporal profiles. In the experiment, a maximum average output power of 14.1 mW at 177.3 nm was obtained. The dependence of 177.3 nm output power on the 355 nm pump power was simulated. The calculated results are in good agreement with the measured data. We used the model further to investigate the optical conversion efficiency, pulse width, beam spatial intensity profile and beam quality factor of the generated 177.3 nm light, in particular the effect of beam birefringent walk-off.