Repetitively pulsed, 70-J photolytic iodine laser with excellentoptical and long/reliable operation

The performance of a repetitively pulsed, 70 joule, closed cycle 1.3 μM photolytic atomic iodine laser with excellent beam quality (BQ=1.15) is presented. This BQ was exhibited in the fundamental mode from a M=3.1 confocal unstable resonator at a 0.5 Hz repetition rate. A closed cycle scrubber/laser fuel system consisting of a condensative-evaporative section, two Cu wool I₂ reactor regions, and an internal turbo-blower enabled the laser to operate very reliably with low maintenance. The fuel system provided C₃F ₇I gas at 10-60 torr absent of the photolytic quenching by-product I₂. Using a turbo-molecular blower longitudinal flow velocities greater than 10 m/s were achieved through the 150 cm long by 7.5×7.5 cm² cross sectional photolytic iodine gain region. In addition to the high laser output and excellent BQ, the resulting 8-12 μs laser pulse had a coherence length greater than 45 meters and polarization extinction ratio better than 100:1. Projections from this pulsed photolytic atomic iodine laser technology to larger energies, higher repetition rates, and variable pulse widths are discussed     

Enhanced performance of the iodine monofluoride (491 nm) laser

The impact of substituting HI for CF₃I as the iodine donor in the discharge-pumped iodine monofluoride (IF) laser at 491 nm has been investigated. More than an order of magnitude improvement in output pulse energy has been observed and is attributed to more efficient production of low-lying (v'<5) vibrational levels of the IF (D') ion pair state. Preliminary evidence indicates that vibrational excitation of HI (X¹Σ⁺ ) assists in the relaxation of the D' state population. The increased net small-signal gain of D'→A' (v'=0→v^") transitions in HI-containing gas mixtures has the effect of intensifying the 491-nm (0.15) bandhead relative to the lower gain transitions     

Radiation induced gas-dynamic refractive index changes in an iodinelaser oscillator

Due to the exothermic recombination of ground state iodine atoms I with free radicals C₃F₇ to the parent molecule C ₃F₇I, the gaseous medium of an iodine laser oscillator is subject to spatially inhomogeneous heating. This causes temperature and pressure gradients leading to gas-dynamic motion and thus to density and refractive index changes perturbing the optical quality of the laser medium. Since the strength of the recombination reaction depends directly on the laser intensity via the process of stimulated emission, this coupling can lead to self-termination of the laser radiation. This phenomenon is experimentally and theoretically investigated     

Frequency tuning of a CW atomic iodine laser via the Zeeman effect

A continuously operating, C₃F₇I photolytic 1.315-μm atomic iodine laser has been used to make the first precise observations of frequency tuning of an atomic iodine laser by means of the Zeeman effect. Application of a uniform magnetic field to the gain region of the photolytic iodine laser causes the laser to operate at different frequencies as a function of the strength of the applied field and the polarization of the laser. With the light polarized perpendicular to the applied magnetic field by means of Brewster output windows, the laser could be tuned to frequencies near the 3-4, 2-2, and 3-3 zero-field transitions of the hyperfine spectrum of atomic iodine. With the light polarized parallel to the applied magnetic field the laser could be tuned to two frequencies bracketing the 3-4 zero-field transition and one frequency near the 2-2 transition. Measurements show close agreement between the observed frequency behavior and theoretical models     

超宽光谱类噪声脉冲光纤激光器

报道了一种全光纤超宽带光谱的类噪声脉冲锁模光纤激光器。为了加宽锁模光谱,利用腔内色散管理和非线性技术,使在58m腔内具有小的反常色散,平均色散系数为0.12 ps/nm/km。实验获得了超过1300nm--1750nm超宽带光谱锁模类噪声脉冲,光谱20-dB带宽达到362nm,3-dB带宽达到102nm。类噪声脉冲的光谱宽度远超过掺铒光纤的增益带宽。     

Influences of finite gain bandwidth on dissipative solitons in passively mode-locked Er-doped fiber laser

Dissipative solitons in the passively mode-locked fiber lasers based on the gain medium of erbium-doped (Er-doped) fiber have attracted a lot of interest in recent years. In this paper, we study the influences of finite gain bandwidth on dissipative solitons in passively mode-locked Er-doped fiber laser. We investigate the influences of the finite gain bandwidth on pulse duration, pulse peak power and single pulse energy of dissipative solitons. The results show that gain bandwidth of the gain medium has influence on dissipative soliton characteristics in passively mode-locked Er-doped fiber laser. The research in this paper has important theoretical and practical significance.     

脉冲声光主动锁模Nd:YAG激光器

本文描述一台脉冲泵浦、声光调制器锁模、电光Q开关放大的Nd:YAG激光器.该激光器输出的脉宽从200微微秒到1毫微秒,单脉冲能量约为0.1毫焦耳,脉冲序列峰值的稳定性优于90%.     

A parametric study of the output of the optically pumped continuouswave CF4 laser

A parametric study of laser output versus CF₄ pressure and temperature was performed and correlated with a model for the gain in the system, which includes the relevant relaxation processes. Lasing in CF₄ was observed at temperatures below 170 K. Cooling the CF₄ gas, the output power of the laser increased from 3 mW at 142 K to 5 mW at 113 K, when 4% of the radiation was coupled out. Chopping the pump, the 16-μm signal consisted of a peak decaying in approximately 2 ms, superimposed on a CW background. This decay is caused by the slow relaxation in the CF₄ laser, resulting in filling of the lower laser level. For the CW CF₄ laser, vibrational relaxation from the laser lower level is even slower than diffusion to the cold cell walls. To increase the relaxation rate, HD was added. In this molecule, the J=1→3 rotational transition at 447 cm^-1 is almost resonant with the ν₂ vibration in CF₄. Maximum CW output was increased by 25% in a mixture containing 10% HD. At the same time, the lasing pressure range was extended     

Chemical oxygen-iodine laser using a new method of atomic iodine generation

The chemical oxygen-iodine laser (COIL) with a new chemical method of atomic iodine production was investigated. In this system, iodine atoms are formed in the COIL cavity by the fast chemical reaction of hydrogen iodide with chlorine atoms that are also produced chemically. It was found that, in the absence of singlet oxygen, the ground state atomic iodine can be produced with a high yield (80%-100%). In gas containing singlet oxygen, a gain on 3-4 electronic transition in iodine atom was achieved (0.35% cm/sup -1/). Both the concentration of atomic iodine and the gain depend substantially on the ratio of reacting gases and the penetration of secondary gases into the primary gas flow. In laser experiments, effects of the flow rate of reacting gases and their penetration on the laser output power were found. The output power of 310 W was attained at chlorine flow rate of 27 mmol/spl middot/s/sup -1/ corresponding to chemical efficiency of 12.7%. This was the first time the gain and laser output power were achieved in the COIL with atomic iodine generated by the proposed method.     

Characteristics of the electron beam pumped iodine monofluoride laser

Electron beam pumping of Ar/CF3I/NF3mixtures yields optical pulse lengthssim0.5 mus from iodine monofluoride. Laser efficiency in this system is ∼0.04 percent. Laser performance is limited by the formation of molecular iodine. The formation of molecular iodine in the excited state (I*2) reduces the number of iodine atoms available to form IF*. In the ground state, molecular iodine (I2) absorbs the IF* laser emission at 485 and 491 nm.     

Characteristics of organic dye lasers as tunable frequency sources for nanosecond absorption spectroscopy

The properties of 1, 1' diethyl-γ-cyano-2,2'-di-carbocyanine-tetrafluoroborate (DTCDCT)and 1, 1'-diethyl-γ-nitro- 4, 4'-di-carbocyanine-tetrafluoroborate (DTNDCT) lasers have been investigated. High-efficiency (25 percent) spectral narrowing of the normal 150-Å-wide, 2-MW output of DTCDCT (around λ 7600 Å) to <0.01 Å, corresponding to a single longitudinal mode, is achieved with a novel longitudinally pumped (by giant pulse ruby laser) dye laser cavity. Beam divergence is <0.5 mrad, and spectral tunability is obtained by rotating the echelle grating and Fabry-Perot etalon cavity elements. DTNDCT transversely pumped by a mode-locked ruby laser (>150 MW peak power) produces a train of 100 percent modulated mode-locked dye laser pulses whose risetimes (<0.5 ns) and pulse widths (0.6 ns) are detector limited. The production of broad continua for nanosecond absorption spectroscopy is also described, together with measurements on the synchronization of the pumping and dye laser pulses. Finally, the direct spectrographic detection of near-resonant optical-frequency Stark effects in potassium is briefly described. Employing the DTCDCT continuum as absorption source, a red shift of75 times 10^{-3}cm^-1of the λ 7699-Å resonance line was detected for a ruby laser perturbing field of power density ∼ 30 MW/cm^-2.     

Active mode locking with hybrid lasers

We present the results of a numerical study of active mode locking with hybrid lasers which contain an inhomogeneously broadened laser medium and an homogeneously broadened laser medium. The spectral, pulse, and gain characteristics of actively mode-locked hybrid lasers and the influence of the unsaturated gain, the saturation power, and the homogeneous linewidth on the pulse coherence and bandwidth are studied. The simulations show that coherent and shorter pulses are generated as compared to that by either an inhomogeneously broadened medium or a homogeneously broadened medium alone. Varying the unsaturated gain or the saturation power of the gain medium are two equivalent ways to obtain the same maximal coherent pulse bandwidth for given gain media. When different gain media can be selected, a larger pulse bandwidth can be obtained with the use of a broadband homogeneously broadened medium     

78 fs被动锁模掺Er3+光纤激光器

用性能稳定的976 nm激光二极管(LD)作为抽运光源,利用非线性偏振旋转(NPR)作为可饱和吸收体,实现了环形腔结构的被动锁模掺Er3 光纤激光器.在抽运功率为57 mW时,通过调节与波长无关的全光纤在线偏振控制器,获得了谱线宽度为40.8 nm,中心波长1544.0 nm,脉冲宽度为78 fs的稳定飞秒脉冲激光,其重复频率为11.18 MHz,平均输出光功率为5.4 mW,单个脉冲能量为0.5 nJ,峰值功率为6200 W.     

1.7 μm全光纤锁模脉冲掺铥光纤激光器研究

1.7 μm超短脉冲光纤激光器在生物成像和材料加工等领域具有重要的应用前景,受到了科学家们的极大关注。基于非线性偏振旋转锁模技术,实验搭建了全光纤结构的1.7 μm锁模脉冲掺铥光纤激光器。通过在激光器内加入光纤滤波器抑制掺铥光纤中的长波激光发射,同时采用纤芯泵浦的方式有效获得了1.7 μm波段的增益。激光器输出脉冲的光谱中心波长为1733 nm,3 dB带宽为6.3 nm。锁模脉冲的重复频率为19.56 MHz,平均功率为1.4 mW。同时,数值模拟了脉冲在激光器的腔内演化。文中提出的1.7 μm全光纤锁模激光器有利于进一步提高1.7 μm激光源的稳定性和集成度,在生物成像等领域具有重要的应用价值。     

Review of CW high-power CO2lasers

Various forms of CO2lasers have achieved CW powers in the 60-kW range, operating efficiencies approaching 30 percent, pulse energies of approximately 2000 J, pulsewidths less than 1 ns, peak pulse powers in excess of 10⁹W, a frequency stability of a few parts in 10¹², and sealed-off tube lifetimes of many thousands of hours. In addition, the laser can be easily Q-switched as well as gain-switched and has been electrically, optically, gas-dynamically, and chemically pumped. In addition to all these attributes, the CO2laser output wavelength lies within one of the best atmospheric windows. It should be no surprise then that during the last eight years, the CO2laser has firmly established itself as a candidate for recognition as the most important among the numerous laser devices presently known. Depending on the gas pressure, gas flow rate, pumping mechanisms, gas mixture, etc., CO2lasers can exhibit a wide range of noise, bandwidth, gain, and power saturation characteristics. This flexibility enables a designer to optimize the performance of CO2laser stable-frequency master oscillators; power oscillators; low-noise high-gain preamplifiers; intermediate-power or high-power amplifiers. As a result, CO2laser oscillator-amplifier chains can be designed utilizing guidelines similar to those which have been extensively applied in the design of transmitters in the RF and microwave region of the electromagnetic spectrum.     

Simultaneous generation of two independently tunable single-mode emissions from a hybrid TEA CO2laser

Results of a parametric study of the operation of a dual-cavity hybrid CO2laser system consisting of a common TEA section and two low-pressure gain sections are presented. While the laser pulse buildup time for each cavity was insensitive to the discharge current of the CW gain section, it changed by up to 400 ns on changing the gas pressure. This permitted generation of temporally smooth and synchronized emission pairs corresponding to various combinations of rotational lines belonging to the 9 and 10 μm vibrational bands. The observed dependence of laser pulse delay on gas pressure in the CW gain section is in good qualitative agreement with numerical results based on a simple phenomenological model.     

电引发脉冲氧碘化学激光器的增益

本文对脉冲氧碘化学激光器的增益性能进行了理论估算。碘原子由CH_3I电离产生。研究了各种压力条件下成份比和CH_3I离解度对增益系数的影响。     

全正色散被动锁模掺镱全光纤环形激光器

采用976 nm半导体激光器为泵浦源,高掺杂Yb3+光纤为增益介质,利用非线性偏转效应实现被动锁模.得到了中心波长为1046 nm,光谱宽度为24 nm,脉冲宽度为54 ps,平均输出功率为93 mW的超短脉冲.通过缩短腔长,获得了较高的重复频率,达到41 MHz.     

Short-pulse generation with broad-band tunability fromsemiconductor lasers in an external ring cavity

Short optical pulses are generated by actively mode locking semiconductor lasers in an external ring cavity with a very broad tuning range from 795 to 857 nm. The wide tunability is possible because the gain bandwidth is broadened by the use of asymmetric dual quantum wells for the semiconductor laser material. Assuming a Gaussian shape, the generated pulses have pulsewidths of 13-21 ps and spectral widths of 24.5 Å for the tuning range. The mode-locked spectrum contains almost no amplified spontaneous emission noise     

Temporal Behavior of the Pump Pulses,Residual Pump Pulses,and THz Pulses for D<Subscript>2</Subscript>O Gas Pumped by a TEA CO<Subscript>2</Subscript> Laser

Temporal behavior of the pump pulses, residual pump pulses, and THz pulses for optically pumped D₂O gas molecules was investigated by using a tunable TEA CO₂ laser as the pumping source. The pulse profiles of pump laser pulses, residual pump pulses, and the THz output pulses were measured, simultaneously, at several different gas pressures. For THz pulse, the pulse delay between the THz pulse and the pump pulse was observed and the delay time was observed to increase from 40 to 70 ns with an increase in gas pressure from 500 to 1700 Pa. Both THz pulse broadening and compression were observed, and the pulse broadening effect transformed to the compression effect with increasing the gas pressure. For the residual pump pulse, the full width at half maximum (FWHM) of the main pulse decreased with increasing gas pressure, and the main pulse disappeared at high gas pressures. The secondary pulses were observed at high gas pressure, and the time intervals of about 518 and 435 ns were observed between the THz output pulse and the secondary residual pump pulse at the pressure of 1400 Pa and 1700 Pa, from which the vibrational relaxation time constants of about 5.45 and 5.55 μs Torr were obtained.