Frequency measurements in the 9μm spectrum of CF3Br

Carbon dioxide laser saturation spectra of CF₃ Br have been explored with a view to hyperfine spectroscopy and references for frequency standards in the 9μm band of the carbon dioxide laser. Spectra have been obtained using the laser transitions 9R(16)-9R(30). and show many saturation features in each case. Several of the stronger features have been referenced directly to CO₂ frequencies with an estimated accuracy of 25 kHz. Spacings between the hyperfine components are also reported. This work represents some of the first data relevant to 9μm locking to molecular absorptions.     

Measurement of the 1s-2s energy interval in muonium

The 1s-2s interval has been measured in the muonium (&mgr;(+)e(-)) atom by Doppler-free two-photon pulsed laser spectroscopy. The frequency separation of the states was determined to be 2 455 528 941.0(9.8) MHz, in good agreement with quantum electrodynamics. The result may be interpreted as a measurement of the muon-electron charge ratio as -1-1.1(2.1)x10(-9). We expect significantly higher accuracy at future high flux muon sources and from cw laser technology.     

Sub-part-per-billion monitoring of nitric oxide by use of wavelength modulation spectroscopy in combination with a thermoelectrically cooled, continuous-wave quantum cascade laser

We used a thermoelectrically cooled, continuous-wave, quantum cascade laser operating between 1847 and 1854 cm(-1) in combination with wavelength modulation spectroscopy for the detection of nitric oxide (NO) at the sub-part-per-billion by volume (ppbv) level. The laser emission overlaps the P7.5 doublet of NO centered around 1850.18 cm(-1). Using an astigmatic multiple-pass absorption cell with an optical path length of 76 m, we achieved a detection limit of 0.2 ppbv at 10 kPa, with a total acquisition time of 30 s. The corresponding minimal detectable absorption is 8.8 x 10(-9) cm(-1) Hz(-1/2).     

Application of a broadband blue laser diode to trace NO2 detection using off-beam quartz-enhanced photoacoustic spectroscopy

We applied for the first time, to our knowledge, broadband off-beam quartz-enhanced photoacoustic spectroscopy (BB-OB-QEPAS) to trace NO2 detection using a broadband blue laser diode centered at 450?nm. A detection limit of 18?ppbv (parts in 10(9) by volume) for NO2 in N2 at atmospheric pressure was achieved with an average laser power of 7?mW at a 1?s integration time, which corresponds to a 1?σ normalized noise equivalent absorption coefficient of 4.1×10(-9) cm(-1)?W=Hz(1=2). An Allan variance analysis was performed to investigate the long-term stability of the BB-OB-QEPAS-based NO2 sensor.     

Three-level neodymium fiber laser incorporating photonic bandgap fiber

We report a neodymium fiber laser incorporating an all-solid photonic bandgap fiber to suppress the four-level laser transition 4F(3/2)-4I(11/2). We demonstrate lasing at 907 nm on the three-level transition 4F(3/2)-4I(9/2) when pumping at 808 nm. The maximum slope efficiency obtained was 32% with a threshold pump power of 70 mW.     

X-ray spectroscopy measurements of laser compressed,argon filled shells

Argon X-ray lines have been used in the past to diagnose laser-compressed targets. We extend such measurements to: (a) very high densities (ρ ≈ 9 gcm^-3) obtained when imploding small shells with short laser pulses, and (b) lower densities but higher πR values (≈4 mg cm^-2) obtained with large DT-Ar filled shells, imploded with long laser pulses. The 24-beam OMEGA laser has been used with 4–5 TW, 100 ps pulses in (a), and 1.5–2 TW, 1 ns pulses in (b).     

Tunable far-infrared spectroscopy extended to 9.1THz

We synthesized tunable far-infrared radiation at frequencies higher than 9 THz (300 cm (-1)) by mixing CO(2) laser, (15)NH(3) laser, and microwave radiation in a W-Co metal-insulator-metal diode. We used this farinfrared radiation to accurately measure torsion-rotation transitions of CH(3)OH in the 8-9-THz region. We also measured the frequency of the aP(7, 3) (15)NH(3) laser transition.     

大气湍流对激光通信系统的影响

从分析激光在大气湍流场中的传输方程出发,忽略系统中的其它噪声,仅考虑由大气喘流引起的系统误码率,讨论了激光信号在传输过程中的振幅起伏以及强度起伏;推导出由大气湍流引起的光强起伏和系统误码率的关系,结果表明:在弱起伏条件下,对于系统误码率为10－9以下的要求,光强起伏应小于0.67;随着湍流强度C2n的增大,误码率增加很快;采用长波长的激光进行传输可以有效地降低系统误码率.     

联合双原子在组合脉冲辐照下的高次谐波发射

首先采用经典的“三步模型“理论,分析了一维普薛耳-特勒势(P-T势)模型原子在组合脉冲作用下的动力学行为,进而利用该组合脉冲辐照联合双原子模型,通过调节组合脉冲的场幅、相位以及设定原子的核间距,使原子有适当的电离和较大的复合效率,因而在截止位置远达Ip 8Up处获得了效率高达10-9的高次谐波发射.     

Accurate spectroscopic wavelength determination of pulsed lasers

We present a simple, easy, and straightforward spectroscopic approach for the determination of the wavelength of pulsed laser systems with an accuracy of ≤0.006 cm^-1 (180 MHz). This is better than currently realised by the best commercially available wavemeters for pulsed laser systems. As an example, the temperature dependence of the emitted wavelength of a pulsed Nd:YAG laser has been studied in detail. Our measurements indicate that the passively Q-switched monolithic nonplanar ring-oscillator Nd:YAG laser with a free spectral range of the resonator of about 5.8 GHz can be tuned without mode hops over a range of 3.8 GHz. The concept is generally applicable to any other wavelength regions of interest. Received: 9 April 2001 / Revised version: 9 July 2001 / Published online: 19 September 2001     

Strong-field above-threshold photoemission from sharp metal tips

We present energy-resolved measurements of electron emission from sharp metal tips driven with low energy pulses from a few-cycle laser oscillator. We observe above-threshold photoemission with a photon order of up to 9. At a laser intensity of ～ 2 × 10(11) W/cm2 the suppression of the lowest order peak occurs, indicating the onset of strong-field effects. We also observe peak shifting linearly with intensity, with a slope of around -1.0 eV/(10(12) W/cm2). We attribute the magnitude of the laser field effects to field enhancement taking place at the tip's surface.     

Characterization of a near-room-temperature, continuous-wave quantum cascade laser for long-term, unattended monitoring of nitric oxide in the atmosphere

We report on power, spectral linewidth, and mode purity for a cw 5.3 microm quantum cascade laser operated on a thermo-electric cooler. A totally noncryogenic nitric oxide monitor was constructed by integrating this laser with an astigmatic multipass cell and a thermo-electrically cooled infrared detector. The resulting instrument is capable of continuous unattended monitoring of ambient, atmospheric nitric oxide for several weeks with no operator intervention. The detection method was rapid sweep, direct absorption spectroscopy. A detection sensitivity of 0.03 parts in 10(9) is achieved with 30 s averaging time with a path length of 210 m, corresponding to an absorbance path length product of 1.5 x 10(-10) cm(-1).     

High power narrowband pulsed dye laser oscillator-amplifier-system

Construction details and operating characteristics are reported for a pulsed dye laser oscillator followed by a three-stage dye laser amplifier. The system is excited with 220 mJ of the second or120 mJ of the third harmonic radiation of a Nd-YAG laser. With Rhodamine dyes the output energy exceeds 55 mJ (9 MW peak power). Coumarin dyes provide pulses of more than 15 mJ (3 MW). Spectral narrowing to less than 260 MHz or 2.7 × 10 ^-4 nm at 565 nm is achieved by a single intracavity etalon of 37.5 GHz free spectral range. Gas pressure tuning allows a continuous linear variation of the laser frequency over more than 3.9 × 10³ GHz (4 nm at 565 nm). The frequency doubled laser output provides tunable UV light of narrow bandwidth (1.4 × 10^-4 nm) and of peak powers exceeding 3 MW.     

Diode laser spectroscopy of the ν9 band of ethyl chloride

The vibration-rotation spectrum of the ν₉ band of C₂H₅Cl was recorded using a Nicolet 7199 Fourier Transform Infrared Spectrometer; the Q-branch, R(5)-R(6) multiplets, and P(21)-P(22) multiplets were investigated using a tunable semiconductor diode laser spectrometer. Constants derived from these assignments are (cm^?1) ν₉ = 973.8379(2), A⁹ = 1.039516(3), B⁹ = 0.183081(7), C⁹ = 0.164505(8). The line which coincides with the CO₂ laser 10R(6), which has been employed in multiphoton dissociation studies, is tentatively assigned to the 20_{3 18}-21_{3 19} transition. In addition, a very strong coincidence of transitions 19_{9 11}-19_{9 10} and 19_{9 10}-19_{9 11} with the CO₂ 10R(16) line is found, which can provide a good candidate for laser chemistry and infrared double resonance spectroscopy.     

Microstructure and properties of plastic deformed martensite induced by laser shock processing

Firstly, 45# steel was quenched by the NEL-2500A rapidly axial flow CO2 laser. The experimental parameters were the laser power of 750 W, the laser beam diameter of 4 mm, the scanning velocity of 7 mm/s.The thickness of coating layer was 0.1 mm and the width was 8 mm. Secondly, the martensite induced by laser quench was shocked by Nd:YAG laser. The parameters of laser shock processing were the wavelength of 1.06 μm, the pulse duration of 23 ns, and the output energy of 16-20 J. The laser was focused on a spot of φ7 mm. K9 optical glass was used as confinement. The sample was coated with black paint 86-1 (the thickness is about 0.025 mm). By testing and analysis of samples which were treated by laser quench and laser quench+shock with transmission electron microscope (TEM), it was discovered that the surface layer of martensite was deformed plastically by laser shock processing. In the secondary hardened zones,there were a lot of slender secondary twin crystal martensites, dislocation tangles, and cellular dislocations.Compared with that of the hardened zones through laser quench only, the residual stress and mechanical properties of the secondary hardened zones were improved and increased through laser compound method.     

Design and analysis of optically pumped semiconductor VECSEL with ANECz optical control layer

Through the reversible isomerization of trans-cis-trans under the linear polarization light, the molecules of azo materials have the same tropism which is vertical to the polarization of light. This means that azo materials have photo-induced birefringence which is related to optical power and polarization angle of the light. Based on the photo-induced birefringence of azo materials, we design a new type of optically pumped semiconductor vertical external cavity surface emitting laser （OPS-VECSEL） which can control the polarization and frequency of the ejection laser. The functional molecules of azo materials are [3-azo- （4＇nitro）]- （9-ethyl）-carbazole （ANECz）.     

激光诱导金纳米棒图案化光纤SERS探针

研究了激光诱导沉积制备光纤表面增强拉曼散射(SERS)探针,并对探针的SERS性能进行检测。探讨光纤探针制备过程中金纳米棒溶液的浓度对探针灵敏度的影响。结果表明,将不同浓度的金纳米棒溶液进行激光诱导,在光纤端面会形成金纳米棒团簇和分散两种纳米结构。金纳米棒溶液的浓度、激光功率、诱导时间等因素都会对诱导沉积图案产生影响。实验利用功率为5 mW的激光进行诱导,在1.5×10^-9, 1.0×10^-9和7.5×10^-10 mol·L^-1的金纳米棒溶液中,经5 min沉积,制备出不同图案的光纤SERS探针。采用晶种法合成金纳米棒,用透射电子显微镜(TEM)观察金纳米棒形貌,并根据TEM图像分析计算了合成金纳米棒的长径比约为3.8。用扫描电子显微镜(SEM)观察金纳米棒的形貌以及激光诱导沉积后的纤维修饰端形貌,7.5×10^-10 mol·L^-1的金纳米棒溶液进行激光诱导,金纳米棒在光纤端面分布较为分散,而1.5×10^-9和1.0×10^-...     

Saturated amplification of a collisionally pumped optical-field-ionization soft X-ray laser at 41.8 nm

We report the first saturated amplification of an optical-field-ionization soft x-ray laser. The amplifying medium is generated by focusing a circularly polarized 330-mJ, 35-fs, 10-Hz Ti:sapphire laser system in a few-mm cell filled with xenon. A gain of 67 cm(-1) on the 4d(9)5p-4d(9)5d transition at 41.8 nm in Pd-like xenon and a gain-length product of 15 have been inferred at saturation. This source delivers about 5 x 10(9) photons per pulse. The influence of the pumping energy and the laser polarization on the lasing output are also presented.     

Demonstration of a Ni-like Kr optical-field-ionization collisional soft x-ray laser at 32.8 nm

We report the first experimental demonstration of a Ni-like optical-field ionization collisional soft x-ray laser. The amplifying medium is generated by focusing a circularly polarized 760 mJ, 30 fs, 10-Hz Ti:sapphire laser beam in a few mm cell filled with krypton. We have measured a gain coefficient of 78 cm(-1) on the 3d(9)4d 1S0-3d(9)4p(1)P1 transition at 32.8 nm, which is here amplified for the first time. This radiation source represents the shortest wavelength optical-field ionization collisional soft x-ray laser ever produced. The influence of the gas pressure and the pumping energy on the lasing output are also presented.     

Comparison of cw and pulsed operation with a TE-cooled quantum cascade infrared laser for detection of nitric oxide at 1900 cm-1

A quantum cascade laser operating near room temperature with thermoelectric (TE) cooling has been used in both continuous-wave (cw) mode (-9 °C) and pulsed mode (+45 °C) to detect atmospheric nitric oxide using spectral lines at 1900.07 cm^-1 (5.3 μm). The totally non-cryogenic spectrometer integrates the laser with a 69-m astigmatic multi-pass cell and a TE-cooled infrared detector to enable operation for extended time periods without operator attention. The pattern of reflections on the astigmatic cell mirrors has been designed to minimize optical interference fringes, which are substantially greater with cw mode than with pulsed operation. The detection method uses direct absorption with rapid- scan sweep integration to achieve sub-second time response. Detection precision for NO in air of 0.5 parts in 10⁹ Hz^-1/2 (1σ) is obtained in pulsed mode with an Allan variance minimum corresponding to 0.1 parts in 10⁹ after 30-s averaging time. The precision in cw mode improves to 0.1 parts in 10⁹ Hz^-1/2 and 0.03 parts in 10⁹ after 30-s averaging, corresponding to an absorbance per unit path length of 2×10^-10 cm^-1. The advantages and disadvantages of cw compared to pulsed operation are discussed. PACS 07.88.+y; 42.62.Fi; 82.80.Gk; 92.60.Sz