共查询到20条相似文献,搜索用时 15 毫秒
1.
Bimal K. Deka 《International Journal of Infrared and Millimeter Waves》1985,6(12):1285-1294
The thresholds for CO2 laser induced breakdown and their variation with pulse width have been measured at various pressures for Ar, N2 and an 8/1/1 laser mixture of He/CO2/N2 using 3–40 ns duration pulses. These measurements indicate that excited state production plays a dominant role in determining the threshold for nanosecond duration pulses. This has been confirmed by the good agreement obtained between the measured and theoretical thresholds. 相似文献
2.
Experimental and theoretical study of V–I characteristics of UV pre-ionized TEA CO2 laser has been carried out for a variety of gas mixtures emitting different optical pulse shapes suitable for various applications. Coupled differential equations have been solved to model the pulse excitation circuit using the numerically calculated values of ionization coefficient (α), attachment coefficient (β) and drift velocity (Ud) as functions of E/N (i.e. electric field to neutral particle density ratio) for chosen gas mixture. Calculated and experimental V–I characteristics for gas mixtures (CO2:N2:He::1:2:3, 1:1:4, 1:1:5 and 1:0:4.7) show a good agreement. It has been shown that gas mixture has a dominant effect on the delay between pre-ionization and main discharge; thus, determining the long-term stability of discharge. The excitation pulse duration increases with increase in molecular content of gas mixture (i.e. amount of CO2 and N2 in gas mixture). 相似文献
3.
Laser-induced voltage effects in Ca3Co4O9 thin films on tilted LaAlO3(001) substrates grown by chemical solution deposition
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Laser-induced voltage effects in c-axis oriented Ca3Co4O9 thin films have been studied with samples fabricated on 10 tilted LaAlO3(001) substrates by a simple chemical solution deposition method. An open-circuit voltage with a rise time of about 10 ns and full width at half maximum of about 28 ns is detected when the film surface is irradiated by a 308-nm laser pulse with a duration of 25 ns. Besides, open-circuit voltage signals are also observed when the film surface is irradiated separately by the laser pulses of 532 nm and 1064 nm. The results indicate that Ca3Co4O9 thin films have a great potential application in the wide range photodetctor from the ultraviolet to near infrared regions. 相似文献
4.
Thin films of hydrogenated amorphous silicon (a-Si:H) were annealed using CO2 laser radiation (λ=10.6 μm). Changes of optical properties of the treated a-Si:H were investigated using optical transmittance spectroscopy and the angular distribution of intensity of reflected radiation (ADIRR). The CO2 laser annealing influences the spectral characteristics of the real part of refractive index n and absorption coefficient α of light in a-Si:H. This treatment increases the n and α values as well as the Urbach energy of a-Si:H. Simultaneously it decreases the optical energy gap of this material. The changes of optical parameters at the interfaces of a-Si:H–glass substrate and a-Si:H–air were established. 相似文献
5.
Bingyuan Zhang Gang Li Meng Chen Guoju Wang Yonggang Wang 《Optics & Laser Technology》2007,39(5):1094-1097
We report a diode-end-pumped passively Q-switched Nd:GdVO4 laser operating at 1.06 μm with In0.25Ga0.75As being the saturable absorber as well as an output coupler. Q-switched pulses with a pulse duration of 20 ns, pulse energy 4.2 μJ and pulse repetition rate 200 kHz were produced, corresponding to peak power of 210 W. 相似文献
6.
We report on a simple and stable pulse tunable CO2 laser suitable for many investigations in the region around 10m. The pulsed discharge when combined with the passiveQ-switching technique provides pulses of 100 ns duration with a peak power of few kilowatts.Due to the interest in pulsed low-pressure CO2 lasers as useful irradiation sources, extensive investigations have been carried out. In particular, various Q-switching techniques have been developed to generate short CO2 laser pulses [1–4]. 相似文献
7.
A 0.5 cm–1 bandwidth injection-locked KrF laser pumps a rare-gas Brillouin cell to produce a reflected pulse with a leading edge risetime of 1 ns, tunable from 248.1 to 248.7 nm. Consistent with Lamb theory of laser amplifiers, subsequent excimer amplification of this pulse produces an intense 500 ps spike on the pulse leading edge. Stimulated Raman scattering then separates the spike from the parent pulse, yielding a tunable short pulse at the first Stokes (S
1) wavelength. Varying the Raman cell length results in a variable Raman threshold and an adjustable short pulse duration: 250 ps pulses at energies of 3–4 mJ at 268 nm with a 50 cm methane cell and 350 ps, 5 mJ pulses from a 100 cm cell are measured with a streak camera. First pass Raman conversion of the spike toS
1 followed by second pass backward Raman amplification, where the parent 248 nm pulse serves as the pump beam for the reflectedS
1 pulse, yields simultaneousS
1 pulses of 20–25 mJ in the 800 ps range andS
2 pulses of 550 ps at 5–6 mJ near 290 nm. This laser will avoid collision effects during laser excitation and enable quantitative, single pulse imaging of OH radicals in turbulent combustion because of its high pulse energy. 相似文献
8.
F. Chen X. Yu C. Wang R. P. Yan X. D. Li J. Gao Z. H. Zhang J. H. Yu 《Laser Physics》2010,20(6):1275-1278
A diode-end-pumped passively Q-switched 912 nm Nd:GdVO4/Cr:YAG laser is demonstrated for the first time. In a concave-piano cavity, pulsed 912 nm laser performance is investigated
using two kinds of Cr:YAG crystal with different unsaturated transmission (T
U) of 95% and 90% at 912 nm as the saturable absorbers. When the T
U = 90% Cr:YAG is used, as much as 2.6 W average output power for short pulsed 912 nm laser is achieved at an absorbed pump
power of 34.0 W, corresponding to an optical efficiency of 7.6% and a slope efficiency of 20.3%. Moreover, 10.5 ns duration
pulses and up to 2.3 kW peak power is obtained at the repetition rate around 81.6 kHz. 相似文献
9.
A tunable electrooptically Q-switched RF excited waveguide CO2 laser with two channels is presented. Q-switched pulses have been obtained from one of the channels. The peak power is 300 W and the pulse width is 140 ns. CW laser output has been obtained from the other channel, which can been tuned by a PZT. The short-term heterodyne stability can be up to 10−9. 相似文献
10.
P. T. Lang W. J. Knott I. Leipold K. F. Renk A. D. Semenov G. N. Gol'tsman 《International Journal of Infrared and Millimeter Waves》1991,12(10):1135-1142
We report on generation and detection of intense pulsed radiation with frequency tunability in the infrared and far-infrared spectral regions. Infrared radiation is generated with a transversally electrically excited high pressure CO2 laser. A laser pulse of a total duration of about 300 ns consisted, due to self mode locking, of a series of single pulses, some with pulse durations of less than 450 ps and peak powers larger than 20 MW. Using these pulses for optical pumping of a Raman D2O laser, trains of short far-infrared pulses with durations less than 400 ps were obtained. For detection a new ultrafast superconducting detector was used. 相似文献
11.
Jianhui Gu Feng Zhou Kah Tau Wan Tuan Kay Lim Siu-Chung Tam Yee Loy Lam Desheng Xu Zuhai Cheng 《Optics and Lasers in Engineering》2001,35(5)
Passive Q-switching of a diode-pumped Nd : YVO4 laser was demonstrated using GaAs as an output coupler and as a saturable absorber. When pumped with a 3-W diode laser at 809 nm, the highly compact laser produced 12-μJ pulses of 2.2 ns in duration at 1.064 μm in a single transverse mode, corresponding to a peak power of 5.6 kW. 相似文献
12.
We reported a 26 W linearly polarized single-mode Yb-doped photonic crystal fiber amplifier, working at 80 kHz repetition
rate with 4.5 ns duration, corresponding 72 kW peak power. Using a acousto-optic Q-switched Nd:YVO4 laser as the seed source, the 26 W average power of 1064 nm laser was obtained at a repetition rate of 80 kHz from a Yb-doped
photonic crystal fiber amplifier, with 4.5 ns duration, polarization extinction ratio 11 dB and M
2 < 1.2. 相似文献
13.
Fast (6250 Hz) line-of-sight measurements of infrared spectral radiation intensities (Iλ) from a luminous flame and a new deconvolution technique for the estimate of local scalar properties using inverse radiation calculations are reported. Time series data of Iλ for one diametric and nine chord-like radiation paths in a representative horizontal plane were measured. Statistical properties of Iλ, including mean, root mean square (rms), probability density function, autocorrelation coefficient, and power spectral density, were obtained from the time series data. The measured statistical properties of Iλ at two representative wavelengths, which are dominated by carbon dioxide (CO2) and soot radiation, respectively, are reported. The autocorrelation coefficient data show large negative loops with repeatable zero crossings at 20 ms and minimum values as low as −0.2 at 30–40 ms. Radial distributions of mean and rms CO2 mole fractions and temperatures were estimated using inverse calculations of mean Iλ at two different wavelengths dominated by CO2 radiation in conjunction with the relationship of these quantities to mixture fractions. Soot volume fraction distributions were also estimated using inverse calculations of mean Iλ at a wavelength dominated by continuum soot radiation. The estimated local mixture fraction distributions were in reasonably good agreement with sampling data from similar flames. The calculated mean Iλ from 1.4 to 4.8 μm other than those used in the inverse calculations matched the experimental data well. The present method provides non-intrusive measurements of major gas species and temperature statistics in turbulent soot containing flames not accessible to other optical diagnostics. 相似文献
14.
A. A. Serafetinides H. Gonis M. Makropoulou E. Agapitos N. Kavantzas C. Politopoulos D. Yova 《Il Nuovo Cimento D》1995,17(3):213-219
Summary One of the prerequisites for successful laser angioplasty is the ablation of the atherosclerotic lesions, without thermal
or shock-wave damage of the healthy tissue. In this study was evaluated the effectiveness of a TEA CO2 laser, emitting pulses of the lower TEM mode, 100 ns duration, at a repetition rate of 2.4 Hz, for the ablation of cardiovascular
tissue. Normal and atherosclerotic human arteries (post mortem) were irradiated for a range of fluences up to 10J pulse−1 cm−2. After irradiation, the samples were prepared for histologic examination. The results showed that controlled ablation of
normal and atherosclerotic coronary artery can be accomplished with the TEA CO2 laser, with minimal thermal damage. 相似文献
15.
Shu-Di Pan Ke-Zhen Han Xiu-Wei Fan Jie Liu Jing-Liang He 《Optics & Laser Technology》2007,39(5):1030-1032
A coherent UV passively Q-switched diode pumped Nd:GdVO4 laser source is proposed. During pumping of the β-BBO crystal a stable light with power 0.6 W with wavelength 532 nm and pulse duration 9 ns at frequency repetition 16 kHz was applied. The output UV light has a power about 79 mW at wavelength 266 nm during diode-pumping with 8 W incident light. 相似文献
16.
Yanning Yu Chongyi Wan Yan Lv Rongqing Tan Jinwen Zhou Shiming Liu Chong Zhao 《Optics & Laser Technology》2005,37(7):294-562
A high average power line-tunable TEA CO2 laser is described. Average output power up to 3 kW is achieved at repetition rate of 180 Hz. The maximum output power is almost equal among the four spectrum bands of CO2 laser (the P and R branches of 00°1–10°0 and 00°1–02°0 transition bands). Several special technologies including rotating spark gap switching, PCB (printed circuit board) preionization and zeroth-order grating coupling are employed. 相似文献
17.
A technique for generating short pulses of 10.6 μm radiation is presented. This technique produces pulses of 10−9−10−8 s duration of single-mode radiation with diffraction-limited divergence of the beam and good extraction efficiency of the energy stored in the cavity. 相似文献
18.
This work investigates the use of laser-induced gas breakdown for simultaneously igniting and measuring fuel-to-air ratio of CH4–air and H2–air combustible mixtures. The fuel-to-air ratio is determined using the measured spectral peak ratio Io,Hα/Io,OI. Sparks are produced using a single-mode, Q-switched Nd–YAG laser. The laser produces a beam of 6 mm in diameter at the wavelength of 1064 nm and pulse duration of 5.5 ns. The beam optics is designed to have mainly a beam splitter and a focusing lens. The beam splitter is coated to reflect the laser beam and transmit emission lines with wavelengths from 600 to 900 nm which are then collected by a fiberoptic cable and detected by an imaging spectrometer–detector assembly. The results showed a linear dependence of the spectral peak ratio on the equivalence ratio that can be generally expressed by φ=a(Io,Hα/Io,OI)+b, where a and b are the parameters that depend on the gas pressure. Using the least-square curve fitting technique to fit the experimental data, a calibration curve for calculating the equivalence ratio as a function of the ratio of (Io,Hα/Io,OI) was generated. 相似文献
19.
A model is proposed for the thermal and electrical responses of films of the high-T
c superconducting material YBa2Cu3O77−x
to current and optical pulses. Numerical calculations are compared with experimental data for current pulses of duration
100 μs and laser pulses of duration 0.1 ns; this yields improved data on the thermal conductivity of thin YBa2Cu3O77−x
films (1.5–2 W/m·K) and thermal resistance of the film-substrate contact (5×10−8m2·K/W) in the neighborhood of the superconducting transition. This model can be used for optimizing the film structure parameters
and control regimes for switching elements for pulses lasting longer than 0.1 ns.
Zh. Tekh. Fiz. 69, 77–82 (October 1999) 相似文献
20.
P. T. Lang W. J. Knott I. Leipold K. F. Renk A. D. Semenov G. N. Gol'tsman 《International Journal of Infrared and Millimeter Waves》1992,13(3):373-380
We report on generation and detection of intense pulsed radiation with frequency tunability in the infrared and far-infrared spectral regions. Infrared radiation is generated with a transversally electrically excited high pressure CO2 laser. A laser pulse of a total duration of about 300 ns consisted, due to self mode locking, of a series of single pulses, some with pulse durations of less than 450 ps and peak powers larger than 20 MW. Using these pulses for optical with durations less than 400 ps were obtained. For detection a new ultrafast superconducting detector was used. 相似文献