Tunable repetition frequency passively Q-switched Tm,Ho:YLF laser with Cr:ZnS as a saturable absorber

We first report a tunable repetition frequency passively Q-switched 2053 nm Tm,Ho:YLF laser by tuning the tilt angle of the Cr:ZnS saturable absorber. When the pump power is 1.4 W, the pulse repetition frequency can be tuned from 1.6 to 19.4 kHz by changing the position of Cr²⁺:ZnS saturable absorber along the cavity axis. When the Cr²⁺:ZnS saturable absorber is near the Tm,Ho:YLF crystal, the repetition frequency can be tuned from 0.8 to 4.0 kHz by changing the tilt angle of the Cr²⁺:ZnS saturable absorber, furthermore, the pulse width and the pulse energy are near constants of 1.7 μs and 3.5 μJ, respectively.     

Few‐cycle,broadband, mid‐infrared optical parametric oscillator pumped by a 20‐fs Ti:sapphire laser

A few‐cycle, broadband, singly‐resonant optical parametric oscillator (OPO) for the mid‐infrared based on MgO‐doped periodically‐poled LiNbO₃ (MgO:PPLN), synchronously pumped by a 20‐fs Ti:sapphire laser is reported. By using crystal interaction lengths as short as 250 µm, and careful dispersion management of input pump pulses and the OPO resonator, near‐transform‐limited, few‐cycle idler pulses tunable across the mid‐infrared have been generated, with as few as 3.7 optical cycles at 2682 nm. The OPO can be continuously tuned over 2179‐3732 nm (4589‐2680 cm^‐1) by cavity delay tuning, providing up to 33 mW of output power at 3723 nm. The idler spectra exhibit stable broadband profiles with bandwidths spanning over 422 nm (FWHM) recorded at 3732 nm. The effect of crystal length on spectral bandwidth and pulse duration is investigated at a fixed wavelength, confirming near‐transform‐limited idler pulses for all grating interaction lengths. By locking the repetition frequency of the pump laser to a radio‐frequency reference, and without active stabilization of the OPO cavity length, an idler power stability better than 1.6% rms over >2.75 hours is obtained when operating at maximum output power, in excellent spatial beam quality with TEM₀₀ mode profile. Photograph shows a multigrating MgO:PPLN crystal used as a nonlinear gain medium in the few‐cycle femtosecond mid‐IR OPO. The visible light is the result of non‐phase‐matched sum‐frequency mixing between the interacting beams.     

Observation of wave-breaking-free square pulses in a fiber ring laser

We experimentally and numerically demonstrate the generation of square pulses without any wave-breaking in a fiber ring laser. A segment of nonzero dispersion-shifted fiber is used to increase the laser cavity length and to optimize the parameters of the laser cavity. In the experiment, the pulse width can be tuned in a wide range from13.5 to 119.5 ns without wave-breaking while the peak power remains almost constant. The maximum singlepulse energy is up to 65.58 n J at a pump power of 508 m W. Numerical results are in good agreement with the experimental results. Numerical results also reveal the role of cavity length and nonlinearity in generating a square pulse without pulse breakup.     

Generation of multi-wavelength square pulses in the dissipative soliton resonance regime by a Yb-doped fiber laser

Multi-wavelength square pulses are generated in the dissipative soliton resonance(DSR) regime by a Yb-doped fiber laser(YDFL) with a long cavity configuration. The spectral filter effect provided by a passive fiber with low-stress birefringence facilitates the establishment of multi-wavelength operation. Through appropriate control of the cavity parameters,a multi-wavelength DSR pulse can be generated in single-and dual-waveband regions. When the multi-wavelength DSR works in the 1038 nm waveband, the pulse duration can broaden from 2 ns to 37.7 ns. The maximum intra-cavity pulse energy is 152.7 nJ. When the DSR works in the 1038 nm and 1080 nm wavebands, the pulse duration can be tuned from2.3 ns to 10.5 ns with rising pump power. The emergence of the 1080 nm waveband is attributed to the stimulated Raman scattering(SRS) effect. Our work might help a deeper insight to be gained into DSR pulses in all-normal-dispersion YDFLs.     

Stabilized diode laser pumped, idler-resonant cw optical parametric oscillator

We present a diode laser pumped continuous wave, pump-enhanced singly-resonant optical parametric oscillator (OPO). The cavity is stabilized by a Pound?CDrever?CHall scheme using direct modulation of the diode laser. The system provides stable signal powers of up to 220?mW. The wavelength can be tuned between 1.40?C1.60???m for a ring or a linear cavity design by changing the crystal temperature. The relative fluctuations of the stabilized OPO??s wavelength are less than 10^?7 for more than one hour. Using a self-heterodyne technique, we measure a linewidth of the signal wave of 3.5?MHz.     

高性能85mm短腔光学参变振荡器的THz电磁波输出特性分析

报道了以MgO∶LiNbO3为非线性光学介质,采用85 mm长的法布里珀罗单谐振腔结构形式的光学参变振荡器,产生THz电磁波的实验结果。使用波长为1064 nm的Nd∶YAGQ开关脉冲激光器作为抽运光源,通过改变入射角度使参变振荡器的相位匹配条件发生变化。采用Si真空量热器,并利用THz波干涉测量仪;或通过测量闲频光的频率对产生的THz波频率进行了测量。实验表明该参变振荡器输出频率调谐范围为0.9~3.0 THz。在抽运光能量为20 mJ/pulse,脉冲宽度16 ns,重复频率50 Hz条件下得到输出峰值位于1.2 THz,能量为102.5 PJ/pulse的THz波输出。通过引入Si棱镜阵列减小了THz波在晶体中的全反射,从而提高THz波的能量输出。使用金属缝隙探测器,对辐射的THz波的波束水平方向空间分布进行了测量,分析了Si棱镜阵列的衍射效应对THz波束空间分布的影响。     

A self-quenching picosecond distributed feedback dye laser pumped by a picosecond laser pulse

A tunable single short pulse laser system with a transform–limited bandwidth pumped by a picosecond Nd:YAG laser (ca. 120 ps pulse width) is demonstrated. With this configuration, the relaxation oscillations coming from a distributed feedback dye laser cavity are completely removed. Because the pumping pulsewidth is shorter than the lifetime of dye molecule on the upper laser state, the gain of the laser medium is depleted by the first pulse. The laser wavelength could be precisely tuned with the transform-limited bandwidth (for example, a linewidth of 0.02 nm). After amplification, we obtain a single short laser pulse energy up to 500 μJ at the pulsewidth of 8.2 ps.     

Design of high-Q silicon-polymer hybrid photonic crystal nanobeam microcavities for low-power and ultrafast all-optical switching

Owing to the unique optical properties high-Q photonic crystal nanobeam microcavities have been demonstrated in a variety of materials. In this paper the design of high-Q silicon-polymer hybrid photonic crystal nanobeam microcavities is investigated using the three-dimensional plane-wave expansion method and finite-difference time-domain method. We first discuss the design of high-Q nanobeam microcavities in silicon-on-insulator, after which the polymer is introduced into the air void to form the hybrid structures. Quality factor as high as 1 × 10⁴ has been obtained for our silicon-polymer hybrid nanobeam microcavities without exhaustive parameter examination. In addition the field distribution of resonant mode can be tuned to largely overlap with polymer materials. Because of the overwhelmingly large Kerr nonlinearity of polymer over silicon, the application in all-optical switching is presented by studying the shift of the resonant frequency on the change of refractive index of polymer. The minimum switching intensity of only 0.37 GW/cm² is extracted for our high-Q hybrid microcavities and the corresponding single pulse energy is also discussed according to the pumping methods. The total switching time is expected to be restricted by the photon lifetime in cavity due to the ultrafast response speed of polymer. Our silicon-polymer hybrid nanobeam microcavities show great promise in constructing small-sized all-optical devices or circuits with advantages of possessing low-power and ultrafast speed simultaneously.     

High-energy single longitudinal mode 1 ns all-solid-state 266 nm lasers

A single longitudinal mode (SLM) short pulse high energy all-solid-state ultraviolet laser is demonstrated in this paper. Through the use of a master oscillator power amplifier (MOPA) architecture, we have been able to provide high-energy outputs with the combination of short pulses, good beam quality and SLM typically produced by a 1064 nm Nd:YAG laser. The passively Q-switched SLM Nd:YAG laser in a twisted-mode cavity is operated as the seed source. After the seed is amplified by a double-pass pre-amplifier and a single-pass main-amplifier, the 100 μJ, 1064 nm, ∼1 ns seeding pulse was amplified up to 400 mJ energy in the total pulse train. Using a KTP crystal for second-harmonic generation and a CLBO for fourth-harmonic generation, we successfully obtained a short pulse, high energy ultraviolet laser of 266 nm, with the output energy of 108 mJ, pulse width 1 ns and M²<5. PACS 42.65.Ky; 42.72.Bj; 42.60.Da     

Ponderomotive ion acceleration in dense plasmas at super-high laser intensities

Short laser pulses at super-high intensities such as those proposed in the Extreme Light Infrastructure (ELI) project open new prospects for efficient acceleration of ions in overdense plasmas. A simple analytical model and numerical simulations demonstrate that pulses with intensities exceeding 10²² W/cm² may efficiently accelerate ions to high energies up to a few GeV. Maximum ion energy and the energy spectrum of the accelerated ions can be tuned by an appropriate choice of laser pulse intensity and duration at a given plasma density distribution.     

Tunable,narrow linewidth,linearly polarized and gain-switched Cr<Superscript>2+</Superscript>:ZnSe laser

We demonstrate a tunable, narrow linewidth, linearly polarized and gain-switched Cr²⁺:ZnSe laser pumped by a Tm, Ho:YVO₄ laser at 10 kHz pulse repetition frequency. By setting a quartz birefringent filter with a Brewster angle in the cavity, the linearly polarized Cr²⁺:ZnSe laser can be continuously tuned from 2.45 to 2.50 μm, and the output power was almost not changed. In addition, the linewidth was compressed to about 5 nm. At the incident pump power to the crystal of 14 W, the maximum output power of 2.84 W was obtained, corresponding to a slope efficiency of 20.4%.     

Wavelength tunable femtosecond laser based on short Er<Superscript>3+</Superscript>/Yb<Superscript>3+</Superscript> codoped phosphate fiber

A wavelength tunable laser system mode-locked by nonlinear polarization evolution based on a 3 cm-long homemade Er³⁺/Yb³⁺ codoped phosphate fiber has been reported. By simply adjusting the polarization controllers, the central wavelength of the mode-locked spectrum can be tuned over 1537.1–1563.3 nm continuously. Moreover, 264-fs pulse with 3-dB spectral width of 39.6 nm and peak power of 7.8 kW at a 7.55 MHz repetition rate is generated directly from the all-fiber ring cavity.     

Comparison of RTP electro-optic Q-switch and acousto-optic Q-switch in Tm,Ho:GdVO<Subscript>4</Subscript> laser

We demonstrate a tunable, narrow linewidth, linearly polarized and gain-switched Cr²⁺:ZnSe laser pumped by a Tm, Ho:YVO₄ laser at 10 kHz pulse repetition frequency. By setting a quartz birefringent filter with a Brewster angle in the cavity, the linearly polarized Cr²⁺:ZnSe laser can be continuously tuned from 2.45 to 2.50 μm, and the output power was almost not changed. In addition, the linewidth was compressed to about 5 nm. At the incident pump power to the crystal of 14 W, the maximum output power of 2.84 W was obtained, corresponding to a slope efficiency of 20.4%.     

A thermally-insensitive passively Q-switched Cr:YAG/Nd:YAG laser

A passively Q-switched laser with Cr⁴⁺:YAG/Nd:YAG composite crystal using a corner cube prism cavity has been realized, in which the corner cube prism is the key element as it aids the compensation of the thermal lens effect of laser crystal. Compared with plane–plane mirror cavities under the same conditions, the stability of the laser performance using the corner cube prism cavity was improved remarkably over temperatures ranging from −40 to 65 °C. The decrease of Nd:YAG stimulated emission cross section with temperature was considered to be the main reason for the increase of average output pulse energy under the same cycle for the two different cavities when the ambient temperature changed −40 to 65 °C. The mode properties produced by the prism cavity were analyzed, and the theoretical results were verified by experimental observations.     

Tunable high energy giant chirped passively mode-locked Yb-doped fiber laser

A tunable, low-repetition rate, all-normal-dispersion Yb-doped fiber laser (YDFL) that is passively mode locked based on a phase shifted long period fiber grating (PS-LPFG) is demonstrated and proposed. The mode-locking mechanism of the laser is based on nonlinear polarization evolution (NPE). Using a PS-LPFG as the spectral filter in the laser cavity, the mode-locked output wavelength can be tuned continuously and smoothly over a spectral range of 10 nm, which is the first time implementation of a tunable giant chirped pulse with all-fiber format bandpass filter in YDFL. The maximum output pulse energy is 38.9 nJ at the repetition rate of 2.499 MHz.     

1.3-2.0μm光参量振荡的实验研究

本文首先阐述光参量振荡器的调谐原理及其温度调谐的计算.接着讨论研制光参量振荡器的若干技术问题.最后给出信号单谐光参量振荡的实验结果.波长谐范围为1.3—2.0μm.当波长调谐到1.9μm且工作重复率为10PPS时,输出能量为0.37mJ/脉冲.     

Rapidly tuning miniature TEA CO2 laser – rotating mirror and grating mechanism

In this research, directed toward using differential absorption lidar (DIAL) for measuring concentrations of pollutant gases, a device for rapidly tuning a transversely excited atmospheric-pressure (TEA) CO₂ laser is presented. It is shown that it is possible to utilize a rotating six-sided scanning mirror and a fixed diffraction grating to rapidly switch wavelength over randomly selected lasing transitions in the 9–11 μm region of the spectrum. The scanning mirror and an optical encoder are driven by a hysteresis synchronous motor at a speed of 1500 rpm. A surface-wire-corona preionization was utilized in a cavity. The laser system is highly automated with microprocessor-controlled laser line selection. Single-branch emission at two wavelengths with time interval ⩽10 ms has been obtained from a single cavity TEA CO₂ laser. An accurate line selection has been demonstrated in over 40 transitions at a pulse repetition frequency of up to 100 Hz. The laser energy at first-order couple output was up to 20 mJ per pulse and the pulse width is about 60 ns in an active volume of 36 cm³.     

Design of high-Q cavities in 2D photonic crystals air holes filled with polymer

We design novel photonic crystal heterostructure, substituting the air in the holes with materials of refractive index higher than n = 1. This can be achieved by infiltrating the photonic crystal (PC) with polymer. We theoretically investigate the L₂ cavity with two missing holes in the center, where the six holes surrounding the cavity are locally filled with polymer. We show that cavity modes can be differently tuned depending on the size and the position of the first hole adjacent to the cavity. A photonic microcavity with a high Q factor of 5.5 × 10⁶ and a modal volume V of 0.1919 is demonstrated. We demonstrate that the calculated Q factor for the designed cavity increases by a factor of 22 relative to that for a cavity without displaced and reduced air holes, while the modal volume remains almost constant.     

Fast, low-noise, mode-by-mode, cavity-enhanced absorption spectroscopy by diode-laser self-locking

A new technique of cavity enhanced absorption spectroscopy is described. Molecular absorption spectra are obtained by recording the transmission maxima of the successive TEM_oo resonances of a high-finesse optical cavity when a Distributed Feedback Diode Laser is tuned across them. A noisy cavity output is usually observed in such a measurement since the resonances are spectrally narrower than the laser. We show that a folded (V-shaped) cavity can be used to obtain selective optical feedback from the intracavity field which builds up at resonance. This induces laser linewidth reduction and frequency locking. The linewidth narrowing eliminates the noisy cavity output, and allows measuring the maximum mode transmissions accurately. The frequency locking permits the laser to scan stepwise through the successive cavity modes. Frequency tuning is thus tightly optimized for cavity mode injection. Our setup for this technique of Optical-Feedback Cavity-Enhanced Absorption Spectroscopy (OF-CEAS) includes a 50 cm folded cavity with finesse ∼20 000 (ringdown time ∼20 μs) and allows recording spectra of up to 200 cavity modes (2 cm⁻¹) using 100 ms laser scans. We obtain a noise equivalent absorption coefficient of ∼5×10⁻¹⁰ cm⁻¹ for 1 s averaging over scans, with a dynamic range of four orders of magnitude.     

Wide single-mode tuning of a 3.0- 3.8-mum, 700-mW, continuous-wave Nd:YAG-pumped optical parametric oscillator based on periodically poled lithium niobate

A new optical parametric oscillator (OPO) for the mid-infrared wavelength region of 3-3.8mum with an idler output power of up to 1.5 W has been developed. The singly resonant OPO is pumped by a single-mode, 10-W, continuous-wave Nd:YAG laser and consists of a bow-tie ring cavity with a fan-out periodically poled lithium niobate crystal and a low-finesse intracavity air-spaced etalon. The single-frequency idler output can be continuously tuned over 24 GHz with 700-mW power by tuning of the pump laser. The tuning was demonstrated by recording of an absorption line of ethane with photoacoustic spectroscopy.