Pulse velocities in the self-locked He--Ne laser

An experimental comparison of the pulse and group velocities in a self-pulsing ring laser is presented. It is found that the two velocities are essentially equal near laser threshold, and the group velocity exceeds the pulse velocity by an increasing amount for increasing laser excitation.     

Dynamique des lasers à fibre dopée à I’erbium

The dynamics of the erbium doped fiber laser is analysed both experimentally and theoretically. This laser operates spontaneously in self-pulsing, in sinusoidal or in CW regime. Experiments have allowed to determine the control parameters : the cavity losses, the pumping rate and the ion pairs concentration. An antiphase dynamics is observed when the laser operates simultaneously at 1.55 µn and 1.536 µm. The self-pulsing behavior is attributed to a fast energy transfer which occurs between two neighboring ions (pair induced quenching). A simple model considering the active medium as a mixture of isolated ions and ions pairs is developped and leads to a good qualitative agreement with the experimental results.     

A rate equation analysis of actively mode-locked semiconductor lasers

A rate equation has been used to analyze the actively mode-locked diode laser which is biased with a subthreshold dc current upon which a sinusoidal signal, whose frequency is equal to the mode spacing (or its multiple) of the external cavity, is superimposed. Steady-state operation of the laser enables us to find out many important parameters of the system. Based upon the experimental observations, we have established the time evolution of the injection carrier density which suggests the existence of a subpulse following the main pulse and provides the possibility of predicting the time gap between them. Meanwhile, the average output power of the laser, the threshold condition of the mode-locked oscillator, the arrival time of the main pulse at the gain medium, the temporal difference between the main pulse, and the peak of the small-signal gain have also been derived.     

Frequency locking by injection in dye lasers: Analysis of the CW and delta pulse regimes

Experimental studies of frequency locking by injection are performed using a nanosecond and a microsecond pulse duration dye laser. Either of these two lasers can be used as the master oscillator, and the experimental conditions then lead to two different injection regimes defined as the CW and the delta pulse regime. In both regimes, the locking efficiency, which is measured as a function of the injected flux of the injected wavelength and of the time delay between the two pulses, reaches a value close to unity when the injected flux present in the forced oscillator cavity is at least equal to 10 W · cm^-2. An analytical relation is derived to explain the experimental results. The use of the injection locking technique to probe the progressive narrowing of tuned dye lasers and to monitor the occurrence of the laser threshold is emphasized.     

Generation and quenching of intensity pulsations in semiconductor lasers coupled to external cavities

The behavior of self-pulsing and nonpulsing lasers coupled to external cavities is investigated experimentally and theoretically. We investigate the dependence of the pulsation characteristics on the external cavity length using a saturable absorber model for self-pulsing lasers. It was found that quenching of self-pulsation occurs only for a certain limited range of external cavity length, and the frequencies of external-cavity induced pulsations lies within a certain range determined by the coupling coefficient. Small-signal analysis allows these ranges to be derived analytically. Hitherto, complex pulsation phenomena can be explained very intuitively by interpreting the combined laser-external cavity system as a microwave oscillator with a limited gain band and discrete mode structure.     

中红外砷酸钛氧钾光参变振荡器的实验研究

为了得到高能量中红外激光输出,对电光调Q灯抽运1064nm Nd:YAG抽运复合腔砷酸钛氧钾(KTA)光学参变振荡器(OPO)作了实验研究,在工作频率1Hz时得到OPO输出单脉冲能量6mJ,信号光脉宽10ns,闲频光波长407nm,能量11mJ.在5Hz～40Hz范围单脉冲能量随重复频率增高而降低.实验中采用的复合腔抽运技术有利于提高转换效率,降低起振阈值.使用上述光源对中红外成像器件作实验,在成像系统监视器上观察到激光光斑.这一结果对中红外激光器的研究是有帮助的.     

Characteristics of mode-coupled lasers

The effects of mode-coupling in a gas laser resulting from a time-varying loss within the optical cavity or from the non-linear characteristics of the inverted population are investigated both theoretically and experimentally. The dominant effect resulting from this mode-coupling is that the laser operates as a pulse regenerative oscillator which produces a periodic train of subnanosecond width pulses. The exact repetition frequency is determined by the frequency of the time-varying loss, which must always be set close to a multiple ofc/2L, i.e., the axial mode spacing, to produce sufficient coupling. To produce pulsing without a time-varying loss, it is necessary that theQor loss of the cavity be judiciously adjusted. In this case the repetition frequency is very close to the axial mode spacing. A preliminary experimental investigation has verified the salient features of the analysis. The measured widths of the pulses from a 6328 Å He-Ne laser and from a 4880 Å Argon-Ion laser were 0.5 and 0.25 ns, respectively.     

Microwave photoconductivity and photodielectric effect in thin PbS films obtained from thiocarbamide coordination compounds

The dependences of photoresponse parameters of the microwave absorption caused by the effect of a short pulse of a nitrogen laser (337 nm, 10 ns) in micrometer-thick PbS films on the frequency of a microwave oscillator, intensity of light, and conditions of the film growth are investigated by a cavity method in the 3-cm frequency band. The films were obtained by pyrolysis of aerosol of thiocarbamide coordination compounds at a substrate temperature of 250–500°C. Using the analysis of frequency dependences of the photoresponse, the microwave photoconductivity and the photodielectric effect, which cause a variation in the cavity quality factor and a variation in its resonance frequency, respectively, are investigated separately.     

Perturbation solution of self-pulsing in semiconductor lasers witha saturable absorber

We solve the three-component rate equations for semiconductor lasers with a saturable absorber or for multi-section semiconductor lasers by using a singular perturbation method. The effects of nonlinear gain and spontaneous emission are included in the rate equations. By transforming the rate equations to the generalized coordinates, we eliminate the most rapidly varying term adiabatically for the fast saturable absorber. Then, we solve the two-component nonlinear equations to obtain analytic expressions for parametric dependence of self-pulsing amplitude and self-pulsing frequency. the self-pulsing frequency shifts from the small-signal oscillation frequency to the lower-frequency side as we increase the self-pulsing amplitude. The square of the self-pulsing frequency does not linearly depend on the injection current, in agreement with experimental observations. We also derive an optimum saturable absorber recovery time for the shortest optical pulse generation     

掺钛蓝宝石激光器的增益开关特性研究

实验研究了调QNd:YAG激光器泵浦的增益开关型掺钛蓝宝石激光器的时间特性,泵浦能量水平(泵浦能量/阈值能量)变化范围为2.1～3.8,腔长变化范围为20cm～60cm,并改变了腔的损耗。根据增益开关激光器时间特性的理论,激光脉冲的建立时间和其脉冲宽度取决于泵浦能量水平和腔长,并与腔损耗成反比,而与泵浦脉宽和波形无关,实验结果与理论分析相符。当用10ns脉宽的激光脉冲泵浦时,在20cm短腔长情况下获得了比泵浦光脉宽窄的仅4ns脉宽的激光脉冲。     

信号光脉冲比抽运光窄12倍的内腔式KTP光参量振荡器

在闪光灯抽运的非稳腔Nd∶YAG被动调Q激光器腔内,放置非临界相位匹配KTP晶体,构成内腔式单谐振KTP光参量振荡器(OPO)。研究了输出信号光的波长调谐性能,获得1.57~1.60μm可调谐激光脉冲。实验结果表明,1.57μm信号光的输出能量随着光参量振荡器腔长的增加而减少,脉冲宽度随着腔长的增加而有所变化;抽运能量较大时,转换效率随着抽运能量的增加趋于饱和然后逐渐下降;对此给予了合理的理论解释。当光参量振荡器的腔长为5 cm,1.06μm抽运光脉冲宽度为30 ns时,输出的1.57μm信号光的脉冲宽度为2.5 ns,能量为21.3 mJ。1.57μm信号光的脉冲宽度仅为1.06μm抽运光脉冲的1/12,总的电光能量转换效率为0.128%。     

The performance of X-band Gunn oscillators over the temperature range 30°C to 120°C

The output power of a cavity-controlled Gunn oscillator has been measured at a frequency of 10 GHz, as a function of bias voltage over the temperature range 30°C to 120°C. The measurements were made using 500-ns pulses to avoid significant changes in-device temperature during a pulse, and at a duty cycle of 20:1 to maintain a low mean input power. The device was operated in a coaxial cavity made of invar, and temperature control effected by operating the cavity in an oven. It has been found that ranges of bias voltages exist over which power output and efficiency is extremely sensitive to temperature changes, and that, depending on the particular conditions, power output can either increase or decrease. The effect of increasing temperature has also been found to reduce the bias voltage required to obtain maximum power output and efficiency.     

A simple model describing both self-mode locking and sustained self-pulsing in ytterbium-doped ring fiber lasers

This paper presents a model describing self-mode locking (SML) and sustained self-pulsing (SSP) in a unidirectional ring-fiber laser using only the interaction between the saturated population inversion and the optical signal circulating in the laser cavity. Gain saturation alone is used to explain SML behavior close to laser threshold and the sharp transition to an SSP regime. The model also describes self-pulsing inhibition to the profit of SML for a sufficiently high pump power. Experimental results agree with most model predictions, but the overestimation of the self-pulsing threshold suggests that the phenomenon is furthered by an effect other than gain saturation.     

Dynamical properties of a laser diode with optical feedback from anexternal high-finesse resonator

The effect of coupling optically a laser diode to a high-finesse external resonator is described. The authors take into account multiple roundtrips in the external cavity and the carrier finite life-time in the diode laser. The rate equations are studied analytically. Steady states are obtained and their stability determined. Numerical resolution of the equations leads to predicting self-pulsing modes of operation. To the authors' knowledge, this is the first numerical study of the laser diode rate equations with an infinite number of delay terms. The main result is a stabilization effect due to the high-finesse cavity; neither deterministic chaos nor complicated bifurcation schemes have been found     

外腔式KTP光学参量振荡器的实验研究

利用脉冲氙灯抽运的Nd：YAG被动调Q激光器输出的1．06μm激光脉冲泵浦KTP光学参量振荡器,获得脉宽3ns、单脉冲能量30mJ、中心波长1568nm的信号光输出。信号光脉冲宽度（3ns）比抽运光脉冲宽度（12ns）4,得多。实验表明,随着OPO腔长的增加单脉冲输出能量减小,随着抽运光能晕的增加单脉冲输出．能晕增大,...     

Active-passive mode locking of a flashlamp-pumped dye laser

A simple dye laser system for obtaining relatively high energy, synchronized, picosecond pulses is described. The novel combination of active and passive mode locking within a single flashlamp-pumped dye laser cavity produced 2.5 μJ, sub-10 ps pulses capable of being synchronized to an external event with better than 100 ps accuracy. The single pulse energy was subsequently increased to 40 μJ by using a larger twin flashlamp-pumped oscillator.     

高重频风冷声光调Q光纤激光器实验研究

为了实现功率稳定的风冷高重频脉冲光纤激光器,采用主振荡功率放大结构,对声光调Q的全光纤激光器进行了研究.振荡级采用声光调Q方案,以光纤光栅对为激光器腔镜,915nm激光二极管连续抽运,得到了中心波长1064nm、重复频率10kHz到130kHz可调的激光脉冲输出.采用两级大模场双包层光纤放大,实现了平均功率101W、脉冲宽度328.1ns、3dB光谱宽度0.6nm的激光输出.第二放大级光光转换效率69%,激光器总光光转换效率达62.7%.分析了声光调Q产生的宽种子光脉冲经放大后发生波形畸变的原因.结果表明,采用915nm抽运波长提高了激光器输出激光功率稳定性,在风冷的情况下输出功率长期稳定性优于2%.     

全光纤化自脉冲抑制的连续稳定运转掺镱光纤激光器

光纤中的非线性效应是限制高功率 光纤激光器发展的重要因素。通过抑制激光器时域的不稳定性(自 脉冲现象),可以提升非线性效应的阈值。基于全光纤化的谐振 腔引入了简单的光纤珐珀腔,使噪声抖动降至原先的1/3,并实现了自脉冲 抑制的稳定的连续激光输出。这种简单的腔结构保持了较高的 斜率效率(76.5%),实现了高功率的激光输出(48.7 W泵浦光产 生36.5 W激光)。这种腔结构中的全光纤化谐振腔不仅可以用作稳定的 连续激光运转激光器,而且还可以用作更高功率光纤放大器的种子,用于限 制非线性效应的产生。     

Active harmonic modelocking of an erbium fiber laser withintracavity Fabry-Perot filters

We present both experimental and theoretical investigations of the operation of a harmonically modelocked erbium fiber ring laser stabilized by an intracavity bit-rate etalon. Our model analyzes the effects of cavity components and operating parameters on laser stability and output pulse characteristics. The model predicts the output pulsewidth variation with laser cavity parameters such as cavity length, dispersion, and finesse of intracavity Fabry-Perot etalons. If the laser cavity length is not optimized, a maximum 50% increase in pulsewidth can occur at 5 Gb/s pulse rate. A repetition rate etalon with a finesse of 50 is sufficient to provide a side-mode suppression ratio of over 50 dB in the laser output. We also discuss how detuning from the optimal modulation frequency increases the excess noise that affects the laser stability. The theory predicts a maximum detuning range of ±100 kHz, which agrees with the experimental observations. These theoretical results can guide the design of similar lasers over a wide range of operating parameters