A pump power controlled multiwavelength fiber laser with?adjustable output channels at fixed wavelength

We report an experimental demonstration of multiwavelength erbium-doped fiber laser with adjustable wavelength number exploiting a power-symmetric nonlinear optical loop mirror (NOLM). As the pump power increases from 53?mW to 410?mW, one?Cseven lasing line(s) at fixed wavelength around 1571?nm are obtained. A?theoretical model describing the NOLM and the EDF is established to investigate the effect of the pump power on the lasing characteristics. Numerical results confirm the experiment measurements and indicate that it is the intensity-dependent loss of lasing beams generated in the NOLM that leads to such phenomena.     

Tunable multiwavelength Brillouin-erbium ring-cavity fiber laser with short-length photonic crystal fiber

A multi-wavelength Brillouin-erbium ring-cavity fiber laser utilizing 2-m erbium doped fiber (EDF) and 70-m high nonlinear photonic crystal fiber (PCF) is proposed and demonstrated. The output characteristics and also the impacts of pump and Brillouin pump (BP) on the output spectra are investigated in detail. The output number and wavelength location of Brillouin lines are tunable by adjusting the power of 1465 nm pump and BP, and a 5-channel output within 11 nm (1551–1562 nm) tuning range is achieved by choosing appropriate pump power.     

Tunable subnanosecond laser pulse generation using an active mirror concept

We report (theory, experimental check) an improved approach for generation of a tunable, subnanosecond pulse (0.1–0.4 ns), based on a single pulsation (“spike”) separation from the transient oscillations in a dye laser with active mirror (AMIR). A pumping by 20–50 ns pulses from Q-switched Nd:YAG laser is considered. The separation is in original, two-spectral selective channels cavity, where the forced by AMIR quenched generation at one of the wavelength stops initially started spiking generation at the other wavelength after the first spike development. The AMIR quickly starts the quenching generation at a precisely controlled moment and with necessary intensity thus assuring the desired separation. An advantage is a high reproducibility of the separation for high (~250%) pump power fluctuations combined with tuning in large range (~20 nm). To obtain such an operation we form ~1 ns leading front pump pulse by electrooptical temporal cutting of the input pump pulse and use an optical delay line. This increases also a few times the power in the separated spike (to be ~100 kW). Our approach widens the combinations of lasers for effective applications of spike separation technique (dye lasers excited by Q-switched solid-state or Cu-vapor lasers).     

Tunable twin beams generated by a type-I LNB OPO

We present a novel scheme to separate spatially twin beams generated by a type-I lithium niobate (LNB) optical parametric oscillator near frequency degeneracy. The system is based on a holographic diffraction grating acting as a beam splitter in a balanced detector. The fast and easy temperature tuning of LNB index of refraction allows an easy control of the twin-beam wavelength distance in a range of the order of ∼100 nm. We report correlation spectra measured for different twin-beam wavelength separations (15–60 nm) with a maximum noise reduction of 3.2 dB at 3.5 MHz. The described system exhibited a pump resonance stability longer than 6 h with infrared output power fluctuations within 4% around an average value of ≃2 mW in each beam. The measured oscillation threshold pump power was lower than 31 mW. Received: 7 June 2001 / Revised version: 17 July 2001 / Published online: 10 October 2001     

Yb-doped strictly all-fiber laser actively Q-switched by intermodal acousto-optic modulation

We show an actively Q-switched ytterbium-doped strictly all-fiber laser. Cavity loss modulation is achieved in a tapered optical fiber by core-to-cladding mode-coupling induced by travelling flexural acoustic waves. When the acoustical signal is switched-off, the optical power losses within the cavity are reduced, and then a laser pulse is emitted. Trains of Q-switched pulses were successfully obtained at repetition rates in the range 1–10 kHz, with pump powers between 59 and 88 mW, at the optical wavelength of 1064.1 nm. Best results were for laser pulses of 118 mW peak power, 1.8 μs of time width, with a pump power of 79 mW, at 7 kHz repetition rate.     

非线性光纤环镜在受激布里渊散射慢光级联系统中的可行性研究

基于非线性光纤环镜(NOLM)的脉冲压缩特性,分析了NOLM在基于受激布里渊散射(SBS)慢光级联系统中对延迟脉冲的影响.利用环形结构来模拟多次级联,有效地降低了系统的复杂度,得到了在不同抽运光功率和级联次数下脉冲的延迟输出特性.理论分析表明,NOLM可以有效地抑制SBS慢光级联系统中延迟脉冲的展宽,抽运光功率决定了展宽因子的变化趋势及最终稳定值的大小,展宽因子在级联4次时趋于稳定值,恰当选取抽运光功率可实现脉冲的零展宽延迟;改变抽运光功率和级联次数可以实现延迟量的连续可调,且延迟量理论上不受限制;增大抽 关键词： 慢光 脉冲压缩 非线性光纤环镜 受激布里渊散射     

Picosecond near- to mid-infrared optical parametric oscillator using KTiOAsO4

The operation and characterization of a high-repetition-rate singly-resonant picosecond optical parametric oscillator based on the non-linear material KTiOAsO4 and synchronously pumped by a Kerr-lens-mode-locked Ti:sapphire laser at 81 MHz is described. By utilizing non-critical type II phase-matching in a 10 mm crystal, average near-infrared output powers of 403 mW have been generated at 31% extraction efficiency. The oscillator exhibits a pump power threshold of 230 mW and with the available mirror set can provide signal tuning over 1.116–1.281 μm and idler tuning over 2.260–3.160 μm by tuning the pump wavelength over 770–896 nm. Without dispersion compensation, near-transform-limited signal pulses with durations of 1.01–1.03 ps and idler pulses with 1.61–2.91 ps duration have been obtained for 1.2 ps input pump pulses. This revised version was published online in November 2006 with corrections to the Cover Date.     

Tunable Ytterbium-Doped Fiber Laser Based on a Mechanically Induced Long Period Holey Fiber Grating

We describe a tunable double-clad Yb-doped fiber laser based on a long period fiber grating mechanically induced in a section of single mode holey fiber inserted into the laser cavity. The mechanically induced long period holey fiber grating acts as a wavelength-selective fiber filter whose central wavelength, linewidth, and strength can be tuned by changing the period, the length of the grating, and the applied pressure. The fiber laser gives a ∼12.6 nm tuning range, from ∼1079:4–1092nm, with slope efficiencies of 18.7–26.3% at this wavelength range, with respect to the launched pump power.     

QCW diode-side-pumped Nd:YAG ceramic laser with 247 W output power at 1123 nm

We demonstrate for the first time a diode-side-pumped quasi-continuous-wave (QCW) operation of a 1123 nm Nd:YAG ceramic laser. The single 1123 nm wavelength is acquired through precise coating. With a pump power of 1000 W, an output power of 247 W is obtained, corresponding to an optical–optical conversion efficiency of 24.7%. At the maximal output power, the pulse repetition rate and pulse width are measured to be 1.1 kHz and 180 μs, respectively. The numerical simulations for wavelength selectivity from 1112, 1116 and 1123 nm are discussed in detail.     

Continuous wave optical parametric oscillator for quartz-enhanced photoacoustic trace gas sensing

A continuous wave optical parametric oscillator, generating up to 300 mW idler output in the 3–4 μm wavelength region, and pumped by a fiber-amplified DBR diode laser is used for trace gas detection by means of quartz-enhanced photoacoustic spectroscopy (QEPAS). Mode-hop-free tuning of the OPO output over 5.2 cm^-1 and continuous spectral coverage exceeding 16.5 cm^-1 were achieved via electronic pump source tuning alone. Online monitoring of the idler wavelength, with feedback to the DBR diode laser, provided an automated closed-loop control allowing arbitrary idler wavelength selection within the pump tuning range and locking of the idler wavelength with a stability of 1.7×10^-3 cm^-1 over at least 30 min. Using this approach, we locked the idler wavelength at an ethane absorption peak and obtained QEPAS data to verify the linear response of the QEPAS signal at different ethane concentrations (100 ppbv-20 ppmv) and different power levels. The detection limit for ethane was determined to be 13 ppbv (20 s averaging), corresponding to a normalized noise equivalent absorption coefficient of 4.4×10^-7 cm^-1  W/Hz^1/2. PACS 42.55.Wd; 42.65.Yj; 42.62.Fi     

Modeling erbium–thulium-co-doped fiber amplifier for 1400–1650 nm band

We present numerical models of tri-valence erbium ion and thulium ion-co-doped fiber amplifiers pumped by 800-nm and 980-nm lasers. The rate and power propagation equations of the models are numerically solved to analyze the gain as a function of co-doping concentrations, fiber length and signal wavelength. The results reveal that with 800-nm or 980-nm pump, gain competition exists between 1470- and 1530-nm bands, which may arise from the pump absorption competition and complicated energy transfer between the two types of active ions, and the results further show that the gain spectra may cover 305 nm (1375–1680 nm) for 800-nm pump and 160 nm (1400–1560 nm) for 980-nm pump. The doping concentrations and fiber length may be tuned to reduce the ripple of the gain spectra.     

A tunable diode-laser spectrometer for the MIR region near 7.2 μm applying difference-frequency generation in AgGaSe2

2 and two diode lasers as pump sources are presented. A single-mode Fabry–Pérot-type tunable diode laser (TDL) and an external-cavity diode laser (ECL) were combined to generate radiation in the mid-infrared region near 7.2 μm. With a TDL at a wavelength of approximately 1290 nm and an ECL emitting between 1504 and 1589 nm it was possible to carry out spectroscopic experiments concerning SO₂ at five different phasematching points between 1350 and 1400 cm^-1 by fixing the wavelength of one pump laser and tuning the wavelength of the other. With an input power of 8 mW for the single-mode Fabry–Pérot-type diode laser and 6 mW for the external-cavity laser an output power of about 10 nW was generated. Using the tuning capabilities of the external-cavity laser a spectral region up to 5 cm^-1 could be covered within one scan. Measurements of SO₂ absorption lines at low pressure demonstrate the high-resolution features of the spectrometer. Moreover, these data provide new direct experimental phasematching data for the rarely investigated spectral region at 7.2 μm. Received: 27 October 1997/Revised version: 8 May 1998     

一种基于非线性光纤环镜开关特性的超短光孤子产生方法

提出了一种利用非线性光纤环镜的开关特性将连续波同时转化为亮孤子和暗孤子的新方法 ,即让连续波和另一波长的调制脉冲串共同耦合入光纤环镜 ,交叉相位调制使得一部分连续波被环镜透射 ,其余部分被反射 ;再让透射波和反射波分别在反常色散光纤和正常色散光纤中传输 ,自相位调制和群速度色散之间的相互作用使得透射波和反射波分别演化为亮、暗孤子。数值计算表明 ,该方法不仅可产生脉宽比调制脉冲窄、重复频率比调制脉冲高的亮孤子和暗孤子 ,而且几乎可将全部的连续波能量转化为孤子能量。     

Efficient and compact intracavity-frequency-doubled Nd:GdVO4/KTP laser end-pumped by a fiber-coupled laser diode

A compact and efficient diode-pumped intracavity-frequency-doubled Nd:GdVO₄/KTP green laser is demonstrated with a flat–flat cavity design. With a 1.3 at. % Nd³⁺-doped GdVO₄ crystal and pumped at the weak-absorption peak of 806 nm, the second-harmonic output power at 532 nm was measured to be 1.95 W at an incident pump power of 8.4 W, corresponding to an optical conversion efficiency of 23.2%. The output characteristic at the fundamental wavelength of 1.063 μm was investigated with two different pump wavelengths. More than 4.5-W output power was generated when the laser was pumped at 806.2 nm. Received: 26 July 2000 / Revised version: 18 September 2000 / Published online: 7 February 2001     

Mercury-free emitter pumped by a krypton fluoride molecule pulse-periodic barrier discharge

The characteristics of a pulsed-periodic short-barrier-discharge emitter operating at wavelength λ = 248 nm KrF(X-B) are investigated. The operating mixtures of the UV lamp are low-aggressive krypton-sulfur hexafluoride (SF6) mixtures at a total pressure in the range 1–50 kPa and a SF₆ partial pressure of 0.1–0.4 kPa. The spectral characteristics of the plasma are studied, and the 248 nm KrF(X-B) band luminosity is optimized in terms of the operating mixture composition, pump voltage, and pulse repetition rate. The mean power of UV emission from the lateral surface of the cylindrical lamp is estimated.     

Intracavity frequency doubling of Yb-doped fiber laser with 540–550 nm tuning

The intracavity doubling of a tunable Yb-doped fiber laser is studied. The phase effects are observed, analyzed and compensated. A smooth wavelength dependence of the second harmonic is obtained in the wavelength interval 540–550 nm. The second-harmonic output is greater than 300 mW at an LD pump power of 18 W.     

Spectral properties of backward stimulated scattering in liquid carbon disulfide

The spectral structure of backward stimulated scattering from a 10 cm-long CS₂-liquid cell is investigated by using Q-switched 10-ns and 532-nm laser pulses with different spectral linewidths. Under a narrow spectral line (∼0.1 cm⁻¹) pump condition, very strong sharp lines near the pump wavelength (λ ₀) position and the first-order stimulated Raman scattering (λ _s1) position can be observed. However, under a wide line (≈1 cm⁻¹) pump condition, only a strong and superbroadening spectral band can be observed mainly in the red-shift side of the pump wavelength. The different spectral features under these two conditions can be explained by a competition between stimulated Brillouin, Raman, and Rayleigh-Kerr scattering. Under both pump conditions, the broadening spectral distributions are not consistent with the predictions given by stimulated Rayleigh-wing scattering theories, but can be interpreted well utilizing the theoretical model of stimulated Rayleigh-Kerr scattering. Zh. éksp. Teor. Fiz. 112, 1563–1573 (November 1997) Published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor.     

High-power mid-infrared tunable optical parametric oscillator based on 3-mm-thick PPMgCLN

The experimental results of a high-power tunable mid-IR laser are presented. The optical parametric oscillator (OPO) with a 3-mm-thick PPMgCLN crystal was pumped by a 1.064 μm pulse laser. When the pump power of the 1.064 μm laser was 151 W at 10 kHz, and the operating temperature of the PPMgCLN with 5% MgO doping was 100°C, average output power of 23.7 W at 3.91 μm was obtained with a slope efficiency of 18.2% for the idler resonant OPO. The variation of the 3.91 μm output power was about ±4% in 10 min continuous operation. The beam quality factor M ² was less than 2.6. The average output power of 27.4 W at 3.91 μm was also obtained with 151 W pump power and the slope efficiency of 20.9% for the signal resonant OPO by changing the coating parameters of the OPO cavity mirrors. The mid-IR wavelength tunability of 3.7–4.0 μm can be achieved by adjusting the temperature of a 29 μm period PPMgCLN crystal from 200 to 30°C.     

Amplified luminescence in InGaAs/AlGaAs laser diode arrays at high pump levels

The development of amplified luminescence fluxes in powerful InGaAs/AlGaAs laser diode arrays (lasing wavelength 940–960 nm) has been studied experimentally and theoretically at pump levels above the threshold value. Flux density values for amplified luminescence propagation along (1.88⋅10⁹ W/m²) and across (1.21⋅10⁹ W/m²) the laser diode array cavity axis have been evaluated for the threshold pump level at room temperature (293 K). The contribution of the recombination rate induced by the amplified luminescence to the threshold current generation of the laser diode array reaches 7%. It has been shown that the amplified luminescence flux density is increased by 49% as the pump level rises from one to three threshold values.     

High-efficiency,high-repetition-rate,temperature-tuning optical parametric oscillator based on periodically poled MgO-doped lithium niobate

We report a compact and viable source of high-efficiency, high-repetition-rate, temperature-tuning, mid-IR optical parametric oscillator (OPO) based on periodically poled MgO-doped lithium niobate (PPMgOLN) pumped by a homemade high power AOM Q-switched Nd:YVO₄ laser centered at 1.064 μm. With an optimal plane-concave resonator configuration, average output power of 5.7 W at 2.73 μm was obtained when the pump power was 25 W at the repetition rate of 80 kHz. The conversion efficiency from the 1.064 μm laser to the 2.73 μm laser was 22.8%. Temperature tuning of the OPO yielded a signal wavelength range from 1.67 to 1.75 μm and an idler wavelength in the range of 2.72 to 2.92 μm.