共查询到20条相似文献,搜索用时 46 毫秒
1.
We present a novel system design that can generate the optimized wavelength-tunable optical pulse streams from an uncooled gain-switched Fabry–Perot semiconductor laser using an optical amplifier as external light source. The timing jitter of gain-switched laser has been reduced from about 3 ps to 600 fs and the pulse width has been optimized by using our system. The stability of the system was also experimentally investigated. Our results show that an uncooled gain-switched FP laser system can feasibly produce the stable optical pulse trains with pulse width of 18 ps at the repetition frequency of 5 GHz during 7 h continuous working. We respectively proved the system feasibility under 1 GHz, 2.5 GHz and 5 GHz operation. 相似文献
2.
Spectroscopic concentration measurements of ammonia and ethylene were done with a pulsed, distributed feedback (DFB) quantum
cascade (QC) laser centered at 970 cm−1. An astigmatic Herriot cell with 150 m path length was employed, and we compare the results from experiments using inter-
and intrapulse techniques, respectively. The measurements include the detection of ammonia in breath with these methodologies.
In the interpulse technique, the laser was excited with short current pulses (5–10 ns), and the pulse amplitude was modulated
with an external current ramp resulting in a ∼0.3 cm−1 frequency scan. A standard amplitude demodulation technique was implemented for extracting the absorption line, thus avoiding
the need for a fast digitizer or a gated integrator. In the intrapulse technique, a linear frequency down-chirp is used for
sweeping across the absorption line. A 200 ns long current pulse was used for these measurements which resulted in a spectral
window of ∼1.74 cm−1 during the down-chirp. The use of a room temperature mercury-cadmium-telluride detector resulted in a completely cryogen
free spectrometer. We demonstrate detection limits of ∼3 ppb for ammonia and ∼5 ppb for ethylene with less than 10 s averaging
time with the intrapulse method and ∼4 ppb for ammonia and ∼7 ppb for ethylene with the interpulse technique with an integration
time of ∼5 s. 相似文献
3.
Femtosecond lasers together with high resolution optics have given us the ability to achieve submicron ablation spots which can play an important role in specific micromachining applications. Light emitted from the plasma at the sample surface created by a focused femtosecond laser pulse can also be used in laser induced breakdown spectroscopy (LIBS) and allows us to characterize the chemical composition of the target surface with micron-level lateral resolution. The spatial resolution using LIBS has often been defined by measuring the FWHM of the crater size. In this report, we study the application of femtosecond 266 nm laser pulses with very low energies of 10׳s of nanojoules. We have investigated spatial resolution using the detection of thin strips of chromium on silicon substrates and compared the actual width of the chromium versus the experimentally obtained width using LIBS detection. The variation of signal levels for low pulse energies is investigated on chromium surfaces. A spatial resolution of ~1 μm was obtained for detection of chromium from the emission. 相似文献
4.
R. Khare P.K. Shukla G.K. Mishra C. Mukherjee S. Talwar V.K. Dubey P. Saxena J.K. Mittal 《Optics Communications》2009,282(19):3850-3853
We present an analytical and experimental study of a novel confocal optical pulse stretcher (COPS). The simple and passive pulse stretcher consists of two concave mirrors and a scraper beam-splitter and its optical configuration ensures a perfect spatial overlapping of laser pulses at the beam-splitter. The pulse stretcher is compact and suitable for laser pulses of large divergences. The confocal optical pulse stretcher is demonstrated on a pulsed copper vapour laser to convert a 40 ns (1/e2 % points) pulse into a 55 ns with reduction of peak power by a factor of 1.375 without loss of pulse energy. 相似文献
5.
Ultrafast pulsed laser ablation has been investigated as a technique to machine CdWO4 single crystal scintillator and segment it into small blocks with the aim of fabricating a 2D high energy X-ray imaging array. Cadmium tungstate (CdWO4) is a brittle transparent scintillator used for the detection of high energy X-rays and γ-rays. A 6 W Yb:KGW Pharos-SP pulsed laser of wavelength 1028 nm was used with a tuneable pulse duration of 10 ps to 190 fs, repetition rate of up to 600 kHz and pulse energies of up to 1 mJ was employed. The effect of varying the pulse duration, pulse energy, pulse overlap and scan pattern on the laser induced damage to the crystals was investigated. A pulse duration of ≥500 fs was found to induce substantial cracking in the material. The laser induced damage was minimised using the following operating parameters: a pulse duration of 190 fs, fluence of 15.3 J cm−2 and employing a serpentine scan pattern with a normalised pulse overlap of 0.8. The surface of the ablated surfaces was studied using scanning electron microscopy, energy dispersive X-ray spectroscopy, atomic force microscopy and X-ray photoelectron spectroscopy. Ablation products were found to contain cadmium tungstate together with different cadmium and tungsten oxides. These laser ablation products could be removed using an ammonium hydroxide treatment. 相似文献
6.
N. Coppendale L. Wang P. Douglas P. F. Barker 《Applied physics. B, Lasers and optics》2011,104(3):569-576
We describe a high-energy, frequency chirped laser system designed for optical Stark deceleration of cold molecules. This
system produces two, pulse amplified beams of up to 700 mJ with flat-top temporal profiles, whose frequency and intensity
can be well controlled for durations from 20 ns–10 μs. The two beams are created by amplifying a single, rapidly tunable Nd:YVO4 microchip type laser at 1064 nm, which can be frequency chirped by up to 1 GHz over the duration of the pulse. Intensity
modulation induced by relaxation oscillations in the microchip laser during the frequency chirp are virtually eliminated by
injection locking a free running semiconductor diode laser before pulsed amplification. 相似文献
7.
H. Sakata K. Yamashita H. Takeuchi M. Tomiki 《Applied physics. B, Lasers and optics》2008,92(2):243-246
We present a diode-pumped microcavity dye laser composed of a top organic reflector and a bottom inorganic reflector. The
top organic reflector consists of alternate thin films of cellulose acetate and poly(N-vinylcarbazole) doped with coumarin
540A to construct a distributed-feedback (DFB) resonator. Pumped directly by an InGaN-based blue laser diode (LD) with a pulse
duration of 4 ns, the microcavity dye laser exhibited a single-mode oscillation at 563 nm with a threshold pump LD power of
290 mW/pulse. The emission of the microcavity dye laser was measured through an optical fiber, resulting in a peak power of
2.5 mW for a pump LD power of 320 mW.
PACS 42.55.Mv; 42.55.Sa; 42.55.Xi 相似文献
8.
Laser ablation micro-machining tests are conducted on silicon wafer, both in air and under flowing water stream, with the use of 355 nm-X AVIA laser. Effects of laser pulse frequency, power level, scan velocity and focal plane position on the associated laser spatter deposition (in air), irradiated areas (under flowing water film) and taper are investigated. It shows that low frequency, i.e. 30–40 kHz, and high peak power result in smaller spatter and irradiated areas, and the hole taper decreases with increase in pulse frequency. Increase in the laser fluence broadens both the areas and increases the hole taper. Both areas enlarge with the increase of scanning velocity of more than 3 mm s?1. The scan velocity has no effect on hole taper in air environment but inconsistent hole taper is obtained under flowing water stream. Furthermore, moving the focal plane position below the workpiece surface contributes relatively smaller areas of spatter deposition, irradiation and taper in comparison to zero focal plane position. Finally, the differences between laser ablation in air and under water are identified. The reduction in the spatter deposition and irradiated areas around the perimeter of the ablated hole and a smaller taper with the use of laser trepan drilling method in air and under water machining are investigated in this paper. 相似文献
9.
Bindesh Shrestha Peter Nemes Akos Vertes 《Applied Physics A: Materials Science & Processing》2010,101(1):121-126
Laser ablation of single cells through a sharpened optical fiber is used for the detection of metabolites by laser ablation
electrospray ionization (LAESI) mass spectrometry (MS). Ablation of the same Allium cepa epidermal cell by consecutive pulses indicates the rupture of the cell wall by the second shot. Intracellular sucrose heterogeneity
is detected by subsequent laser pulses pointing to rupturing the vacuolar membrane by the third exposure. Ion production by
bursts of laser pulses shows that the drying of ruptured A. cepa cells occurs in ∼50 s at low pulse rates (10 pulses/s bursts) and significantly faster at high pulse rates (100 pulses/s
bursts). These results point to the competing role of cytoplasm ejection and evaporative drying in diminishing the LAESI-MS
signal in ∼50 s or 100 laser pulses, whichever occurs first. 相似文献
10.
A. Matei J. Schou C. Constantinescu P. Kingshott M. Dinescu 《Applied Physics A: Materials Science & Processing》2011,105(3):629-633
Thin films of lysozyme and myoglobin grown by matrix assisted pulsed laser evaporation (MAPLE) from a water ice matrix have
been investigated. The deposition rate of these two low molecular weight proteins (lysozyme: 14307 amu and myoglobin: 17083 amu)
exhibits a maximum of about 1–2 ng/cm2 per pulse at a fluence of 1–2 J/cm2 and decreases slowly with increasing fluence. This rate is presumably determined by the matrix rather by the proteins. A significant
fraction of the proteins are intact in the film as determined by MALDI (Matrix assisted laser desorption ionization) spectrometry.
The results for lysozyme demonstrate that the fragmentation rate of the proteins during the MAPLE process is not influenced
by the pH of the water solution prior to freezing. 相似文献
11.
Output performance of a continuous-wave (CW) laser diode end-pumped passively Q-switched Tm,Ho:YLF laser is demonstrated with a Cr:ZnS crystal as the saturable absorber. We particularly investigate the influence of saturable absorber's position in the resonator when the Cr:ZnS crystal is placed close to and far from the laser beam waist. We compare the experimental results at the two different positions, and find that the laser shows unusual output characteristics when the Cr:ZnS saturable absorber is placed close to the beam waist. The pulse width and the pulse energy almost keep constant, measured about 1.25 μs and 4 μJ respectively, when the pump power is changed in the range of 1–1.9 W. Moreover, the pulse repetition frequency can be tuned between 1.3 kHz and 2.6 kHz by changing the pump power. The output wavelength of the passively Q-switched laser shifts to 2053 nm from 2067 nm in CW operation. 相似文献
12.
We use a single walled carbon nanotubes (SWCNTs) absorber to demonstrate a high power mode locking for Nd:YVO4 lasers. Under the pump power of 12 W, continuous wave mode-locked (CWML) pulse were generated with the maximum average output
power of 3.6 W and the pulse duration of 7.6 ps. The peak power and the single pulse energy of the mode-locked laser were
up to 4.9 kW and 37.5 nJ, respectively. To our knowledge, this is the highest average output power of the CWML laser with
the SWCNTs absorber reported. 相似文献
13.
Kai Jiang Chunmei Ouyang Perry Ping Shum Kan Wu Jia Haur Wong 《Optics Communications》2012,285(9):2422-2425
We experimentally demonstrate pulse energy enhancement in an all-fiber passively mode-locked laser operating in the large normal dispersion regime. By increasing the laser cavity length as well as its net cavity dispersion, the proposed laser, which is mode-locked by nonlinear polarization rotation, generates highly chirped dissipative solitons with pulse energies up to 9.4 nJ. The fundamental repetition rate is 2.3 MHz, and the pulse duration is 35 ps. Such low repetition rate as well as wide pulse width makes this mode-locked all-fiber laser a suitable oscillator to directly seed a fiber amplifier, which can be used as compact sources for high-power applications. 相似文献
14.
Peel Christopher S. Fang Xiao Ahmad S. Rafi 《Applied Physics A: Materials Science & Processing》2011,103(4):1131-1138
This paper presents an analysis of the rate of bubble expansion and an estimate of maximum bubble diameter and bubble lifetime
prior to collapse. Such data are needed for the optimization of system parameters for elemental analysis in water by laser-induced
breakdown spectroscopy (LIBS). Two techniques were used for this study: pump-probe beam deflection and high-speed photography.
Plasma in the water bulk was generated by a focussed laser pulse with energy of 140 mJ and pulse duration of 10 ns, operating
at the fundamental Nd:YAG laser wavelength (1064 nm). Reasonable agreement on the value of maximum bubble diameter was obtained
between the photographic and probe beam deflection results. Reasonable agreement for the total duration of the oscillating
cavitation bubble was also obtained for the two techniques, with a mean value of ∼800 μs. A comparison between empirical results
and predictions based on the Rayleigh equation is also presented. 相似文献
15.
A tunable single short pulse laser system with a transform–limited bandwidth pumped by a picosecond Nd:YAG laser (ca. 120 ps
pulse width) is demonstrated. With this configuration, the relaxation oscillations coming from a distributed feedback dye
laser cavity are completely removed. Because the pumping pulsewidth is shorter than the lifetime of dye molecule on the upper
laser state, the gain of the laser medium is depleted by the first pulse. The laser wavelength could be precisely tuned with
the transform-limited bandwidth (for example, a linewidth of 0.02 nm). After amplification, we obtain a single short laser
pulse energy up to 500 μJ at the pulsewidth of 8.2 ps. 相似文献
16.
We report here an experimental study of the ionic keV X-ray line emission from magnesium plasma produced by laser pulses of
three widely different pulse durations (FWHM) of 45 fs, 25 ps and 3 ns, at a constant laser fluence of ∼1.5 × 104 J cm − 2. It is observed that the X-ray yield of the resonance lines from the higher ionization states such as H- and He-like ions
decreases on decreasing the laser pulse duration, even though the peak laser intensities of 3.5 × 1017 W cm − 2 for the 45 fs pulses and 6.2 × 1014 W cm − 2 for the 25 ps pulses are much higher than 5 × 1012 W cm − 2 for the 3 ns laser pulse. The results were explained in terms of the ionization equilibrium time for different ionization
states in the heated plasma. The study can be useful to make optimum choice of the laser pulse duration to produce short pulse
intense X-ray line emission from the plasma and to get the knowledge of the degree of ionization in the plasma. 相似文献
17.
Dual-wavelength asynchronous and synchronous mode-locking operation by a Nd:CLTGG disordered crystal
J.-L. Xu S.-Y. Guo J.-L. He B.-Y. Zhang Y. Yang H. Yang S.-D. Liu 《Applied physics. B, Lasers and optics》2012,107(1):53-58
We have developed a diode-pumped passively mode-locked Nd3+:CLTGG laser operated at 1059 and 1061 nm with a semiconductor saturable absorber mirror (SESAM). The relative intensity of
the two spectrum wavelengths is adjustable, allowing asynchronous and synchronous generation of the dual-wavelength pulses.
In synchronous mode-locking regime, a total average output power of 383 mW was obtained with pulse duration of 3.5 ps and
repetition rate of 42 MHz. The two spectral bands of 1059 and 1061 nm had the same intensities and areas, indicating 1:1 for
the pulse energy ratio. It is desirable for efficiently generating a terahertz wave by difference-frequency generation. 相似文献
18.
Ayan Ray Amitava Bandyopadhyay Sankar De Biswajit Ray Pradip N. Ghosh 《Optics & Laser Technology》2007,39(2):359-367
A very simple and inexpensive tunable semiconductor diode laser controller is designed for stable operation of the diode laser. The diode laser controller is stable within +/−8 μA and +/−10 mK, respectively. The noise spectrum of the current controller is studied by FFT analysis. We have used our home-made diode laser system in a tunable diode laser absorption spectrometer (TDLAS) to probe weak overtone transitions of water vapour molecule. The diode laser wavelength is coarsely tuned by changing the operating temperature to probe (2, 1, 1)←(0, 0, 0) band overtone transitions of water vapour within 818–835 nm. To demonstrate line shape study, seven transitions are scanned by ramping the drive current of the diode laser (at constant operating temperature) under different perturber (laboratory air) pressures within the sample cell. A balanced detector and a lock-in amplifier are used for phase sensitive detection purpose. Small current modulation amplitude, balanced detection and proper adjustment of the lock-in amplifier help to obtain a S/N ratio ranging from 100 to 7 using a small sample path length of 1.5 m. Experimentally obtained derivative spectrum is numerically integrated to reveal the original line shape and fitted with a nonlinear least squares fitting program to extract air broadening coefficients and line strength parameters. The spectroscopic line parameters are compared with the results from HITRAN database. 相似文献
19.
Gang Zhang Shengzhi Zhao Guiqiu Li Dechun Li Kejian Yang Kang Cheng Chao Han Bin Zhao 《Optics Communications》2012,285(15):3289-3294
The Q-switched and mode-locked (QML) performance in a diode-pumped Nd:Lu0.2Y0.8VO4 laser with electro-optic (EO) modulator and GaAs saturaber absorber is investigated. In comparison with the solely passively QML laser with GaAs, the dual-loss-modulated QML laser with EO and GaAs can generate pulses with higher stability and shorter pulse width of Q-switched envelope, as well as higher pulse energy. At the repetition rate 1 kHz of EO, the pulse width of Q-switched pulse envelope has a compression of 89% and the pulse energy has an improvement of 24 times. The QML laser characteristics such as the pulse width, pulse peak power etc. have been measured for different small-signal transmittance (T0) of GaAs, different reflectivity (R) of output coupler and modulation frequencies of the EO modulator (fe). The highest peak power and the shortest pulse width of mode-locked pulses are obtained at fe = 1 kHz, R = 90% and T0 = 92.6%. By considering the influences of EO modulator, a developed rate equation model for the dual-loss-modulated QML laser with EO modulator and GaAs is proposed. The numerical solutions of the equations are in good agreement with the experimental results. 相似文献
20.
V.L. Kasyutich R.J. Holdsworth P.A. Martin 《Applied physics. B, Lasers and optics》2008,92(2):271-279
We describe the performance of two mid-infrared laser spectrometers for carbon monoxide, nitrous oxide and nitric oxide detection.
The first spectrometer for CO and N2O detection around 2203 cm-1 is based upon all-diode laser difference frequency generation (DFG) in a quasi-phase matched periodically-poled lithium niobate
(PPLN) crystal using two continuous-wave room-temperature distributed feedback diode lasers at 859 and 1059 nm. We also report
on the performance of a mid-infrared spectrometer for NO detection at ∼ 1900 cm-1 based upon a thermoelectrically-cooled continuous-wave distributed feedback quantum cascade laser (QCL). Both spectrometers
had a single-pass optical cell and a thermoelectrically cooled HgCdZnTe photovoltaic detector. Typical minimum detection limits
of 2.8 ppmv for CO, 0.6 ppmv for N2O and 2.7 ppmv for NO have been demonstrated for a 100 averaged spectra acquired within 1.25 s and a cell base length of 21 cm
at ∼ 100 Torr. Noise-equivalent absorptions of 10-5 and 10-4 Hz-1/2 are typically demonstrated for the QCL and the DFG based spectrometers, respectively.
PACS 42.55.Px; 42.62.Fi; 42.65.-k; 42.72.Ai; 42.68.Ca 相似文献