Detection of atomic oxygen in flames by absorption spectroscopy

The absolute concentration of atomic oxygen in an atmospheric pressure hydrogen/air flame has been measured using Intracavity Laser Spectroscopy (ICLS) based on a dye laser pumped by an argon-ion laser. Absorptions at the highly forbidden transitions at 630.030 nm and 636.380 nm were observed at an equivalent optical length of up to 10 km. The relatively low intensity of the dye laser avoids photochemical interferences that are inherent to some other methods for detecting atomic oxygen. The detection sensitivity is about 6 × 10¹⁴ atom/cm³ and can be improved with better flame and laser stabilization.     

Highly photostable laser solution and solid-state media based on mixed pyrromethene and coumarin

A substantial increase in the photostability of pyrromethene 567 laser dye solutions and in solid polymer media has been achieved by the addition of coumarin C540 laser dye. Up to five times increase in photostability of pyrromethene 567 in solid and two times in solution has been observed. The enhanced photostability is attributed to reduction in the effectiveness of in situ oxygen degradation of pyrromethene by the addition of the coumarin.     

Comparative laser performances of pyrromethene 567 and rhodamine 6G dyes in copper vapour laser pumped dye lasers

Narrowband laser performances and photochemical stability of alcoholic solutions of pyrromethene 567 and rhodamine 6G dyes, under high-repetition rate copper vapour laser (at 510 nm), as well as, high-peak intensity Nd:YAG laser (at 532 nm) excitation have been investigated. We have observed that pyrromethene 567 dye solutions offer higher efficiency, wider tuning range, but lower photochemical stability and higher lasing threshold than that of rhodamine 6G dye solutions. An addition of about 100 mM DABCO, as a singlet oxygen quencher, in pyrromethene 567 dye solutions improved its photochemical stability close to that of rhodamine 6G. The observation of higher slope efficiency, in spite of higher threshold pump energy for pyrromethene 567 dye than that of rhodamine 6G dye solutions, was explained by a predictive model on gain characteristics of both dye solutions as a function of pump energy. PACS 42.55.Mv; 42.55.Rz; 42.70.Hj; 42.70.Jk     

应用于FAGE技术测量OH自由基的激光器波长修正方法研究

研究了一种应用于气体扩张激光诱导荧光(FAGE)技术测量OH自由基的染料激光器波长修正方法。该方法采用镍铝丝热解水汽产生稳定的高浓度OH自由基,利用重复频率为8500 Hz的染料激光器输出波长约282 nm激光作为光源.激发低压腔内热解产生的高浓度高稳定性OH自由基产生荧光,由普通光电倍增管和光电二极管分别探测激发荧光和出腔激光强度。通过延时信号发生器统一触发激光器和高速数据采集卡并结合LabVIEW软件处理得到单位激光强度的荧光积分强度数据。连续两次扫描激光波长,当第二次扫描的荧光积分强度达到第一次最大值的0.95倍时,停止波长扫描,此时的激光器波长位置即为激发线位置。本文首先扫描激光波长,研究了282 nm激发机制下的OH自由基激发谱;然后在Q_1 2激发线位置探究了气体湿度、氧气含量、进气量以及抽速对荧光积分强度和寿命的影响;并分析了镍铝丝热解水的反应机理,初步认为热解中OH自由基主要来源于氧原子与水的反应。在以上荧光积分强度和寿命影响因素的研究基础上,优化了系统参数,使荧光积分强度波动小于±1.9%。连续多次进行波长修正,修正偏差为0.1pm。该方法能够满足气体扩张激光诱导荧光(FAGE)技术定量精确测量大气OH自由基对波长的要求。     

Enhanced photostability of photoluminescent dye-doped solutions and polymers with the addition of dielectric-oxide micro-particles

Organic dye molecules in both solid polymethyl methacrylate and in solution have been found to display greatly enhanced photostability with the addition of micro-particles. Micro-particle doped poly(methyl methacrylate) samples and solutions were prepared doped with the laser dye pyrromethene 567 and rhodamine 6G. Study of the composite dye material as a gain medium in a laser provided a controlled and sensitive test of the photostability. The micro-particle doped samples used as the active laser medium demonstrated a doubling in service life to 0.4 million pulses compared with undoped samples before the output intensity was reduced to one-half. Further addition of a singlet oxygen quencher (DABCO) enhanced the photostability to 0.6 million pulses. Possible explanations discussed include cavity QED effects, surface photophysical and photochemical interactions and thermo-mechanical effects. These observations are relevant to photoluminescent devices and in general to the photostability of organic molecules.     

Laser dyes III: Concepts to increase the photostability of laser dyes

Two approaches of increasing the photostability of the laser dye POPOP are reported. Desensibilisation against singlet oxygen was accomplished either by substitution with electron acceptor groups or by linking the dye molecule with a suitable quencher unit, e.g. tertiary amines. To test the efficiency of the modifications of the dye molecules the rate of their continuous UV-bleaching (λ = 366 nm) was investigated.     

Laser dye mixtures

Properties necessary to obtain efficient laser action from laser dyes are reviewed. It is concluded that the dye added (booster dye) to a laser dye (active dye) solution to increase its efficiency need not necessarily be a laser dye. This is illustrated by considering different spectral locations of a triplet-triplet absorption band present in the booster dye relative to the location of the laser action region (part of the fluorescence spectrum) of the active laser dye. Conditions required for booster dyes to form efficient dye mixtures are given. These observations are used to explain why specific well known laser dye mixtures show efficient, little, or no laser action at all.     

Temporal dynamics of high repetition rate pulsed single longitudinal mode dye laser

Theoretical and experimental studies of temporal dynamics of grazing incidence grating (GIG) cavity, single-mode dye laser pumped by high repetition rate copper vapour laser (CVL) are presented. Spectral chirp of the dye laser as they evolve in the cavity due to transient phase dynamics of the amplifier gain medium is studied. Effect of grating efficiency, focal spot size, pump power and other cavity parameters on the temporal behaviour of narrow band dye laser such as build-up time, pulse shape and pulse width is studied using the four level dye laser rate equation and photon evolution equation. These results are compared with experimental observations of GIG single-mode dye laser cavity. The effect of pulse stretching of CVL pump pulse on the temporal dynamics of the dye laser is studied.     

Undamped relaxation oscillations due to self-gain-switching of laser dye mixtures

Undamped relaxation oscillations were observed from a short, simple dye laser using a laser dye mixture which was pumped at 337 nm using ns pulses. The dye solution contained Rh101 as first laser dye, together with DTDCI in double function as saturable absorber and second laser dye. Two trains of intense laser pulses were generated near 619 and 685 nm, with pulse durations of ca. 4 and 2 times the resonator transit time, respectively. This method of short-pulse generation is related to double mode-locking of dye lasers. Model calculations are used to describe the pulse generation by self-gain-switching, and to estimate radiative and nonradiative contributions towards saturation of the absorber dye.     

Study of synchronously mode-locked and internally frequency-doubledcw dye laser

The analysis of the characteristics of a synchronously mode-locked and internally frequency-doubled dye laser is presented. Dependence of dye laser pulse characteristics on the cavity length mismatch of the pump laser and dye laser is studied. Variation of the minimum pulsewidth with intracavity bandwidth and the harmonic conversion efficiency is presented in the form of graphs.     

Generation of nearly transform-limited pulses in subnanosecond region with TEA nitrogen-laser-pumped dye laser

A dye laser is transversely pumped by a TEA nitrogen laser with 700 ps duration. The dye laser pulse has a spectral linewidth of 0.007 nm and a pulse width of ≈ 140 ps, giving a time-bandwidth product of 1.5. It is pointed out that the fluorescence lifetime of the laser dye plays an important role in generation of laser emission using a long laser cavity under subnanosecond pulse pumping.     

“波长等效激光”作用下铀原子的单色三光子共振电离谱测量

用Nd:YAG532nm激光泵浦的混合染料激光得到了在相当于铜蒸气激光器泵浦染料激光的某个波段上增强的激光输出，测得了铀原子在562-586nm波段内的单色三光子共振电离谱中140个能级，其中575.814和575.836nm两个峰很好地分开了，它们的相对强度也能测定，若用单一染料的激光是难以做到，因为目前尚无合适的染料在上述波段内能有强的激光输出。     

10 ps High Power Laser System at 248 nm

A simple 10 ps KrF laser system consisting of quenched dye laser oscillator pumped by a XeCl laser, a distributed feedback dye laser (DFDL), a three-stage dye amplifier and a two-stage KrF amplifier are described. The output of the laser system is 140 mJ with 10 ps pulse width by using polarization-multiplexing amplification. A focused output laser intensity of about 4×1015 W/cm2 is obtained. The saturation fluence for KrF laser is obtained with this laser.     

10 ps High Power Laser System at 248 nm

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染料激光放大器最佳增益长度研究

在横向泵浦脉冲染料激光器中,虑及染料激发态在激光波长处的吸收,根据稳态运转转条件,应用极值原理,给出其最佳增益与染料长度的关系式。     

染料激光放大器最佳增益长度研究

在横向泵浦脉冲染料激光器中,虑及染料激发态在激光波长处的吸收,根据稳态运转转条件,应用极值原理,给出其最佳增益与染料长度的关系式。     

New efficient laser dye for pulsed and CW operation in the UV

A new laser dye for pulsed and cw operation has been synthesized which can be tuned from 362 nm up to 412 nm. For pulsed excitation with a XeCl excimer laser an energy conversion of 18.5% has been measured at the tuning maximum of the dye; this is the highest efficiency for any known dye in the UV. For cw operation a low laser threshold and a goof efficiency have been observed. The range of tuned cw dye lasers is extended by 30 nm to shorter wavelengths. The dye shows high photochemical stability even at high pump laser power.     

YAG激光器往返损耗和泵浦效率的测量

依据染料调 Q 激光理论,通过实验测量计算染料调 Q YAG 激光器的往返损耗和泵浦效率。讨论染料调 Q YAG 激光器效率的有关问题。     

Power output coupling in a dye laser pumped by a nitrogen laser

A simple model for the operation of a pulsed dye laser, transversely pumped by a nitrogen laser, is presented. We consider the combined effect of the transmission of the laser output coupler, its distance from the dye cell and the saturated gain characteristics of the dye laser medium, on the operation of the laser. Experimental results are interpreted in terms of this model.