All solid-state flash-lamp pumped passive-active mode-locked Nd<sup>3+</sup>:YAG laser is designed and experimentally studded.
Saturation absorber Cr<sup>4+</sup>:YAG with initial transparency 25 and 47% are used as a passive Q-switcher and acousto-optical
fused quartz modulator as an active mode-locker. Efficient length of the laser cavity with fixed mirror positions (1.45 m
spaced) is droved by changes of 100% flat mirror for concave mirrors with different focus lengths. Changeable output mirrors
with transparencies of 15 and 50% are used. Driving of the cavity parameters, laser and acousto-optical modulator power
supply voltages let us to control output pulse train and single pulse parameters. As it goes from the analyses of oscillograms
fixed with pyroelectric detector (τ=0.5 ns) and 1 GHz oscilloscope, over 95% of pulse output energy has been mode-locked.
Average duration of the pulse train envelope of 5 to 50 single pulses at FWHM has been droved within 50 to 600 ns. When
this single pulse duration is controlled but did not exceed 2 ns.
In order to achieve the highest peak power of radiation pulse and highest output energy, the primary circuit parameters
are investigated to optimize the discharge circuit performance of the laser. The structure and the discharge circuit of the
laser are discussed at first. To realize synchronous discharge in two discharge channels, the conjunct electrode device for
two pairs of discharge electrodes is designed. Finally, the results of the experiments on the primary circuit parameters are
given. The discharge is most stable at a pressure of 5.33×10<sup>4</sup>Pa when the pressure of gaseous mixture CO<sub>2</sub>:N<sub>2</sub>:He=1:1:3
is changed from 2.67×10<sup>4</sup> Pa to 6.67×10<sup>4</sup> Pa. The ratio of storage capacitance to peak capacitance is chosen to be about
1.5-7/3, because residual voltage is lower on this condition and residual voltage is adverse to discharge. When the
inductance 330&mgr;H is used, the homogeneous glow discharge in a widest voltage range is obtained. The duration of when the stimuli voltage is increased in
homogeneous glow discharge condition. The discharge circuit allows
charge and discharge and the magnitude of residual voltage decrease the homogeneous glow discharge in a wide range
of pressure of gaseous mixture when these circuit parameters are used. Thus it offers reference to the improvement of
output characteristic of TEA CO<sub>2</sub> laser with two discharge channels.
Five temperature model is used to describe the process of the dynamics preferably in the transversely excited atmospheric-pressure (TEA) CO<sub>2</sub> laser. In this paper five temperature vibrational dynamics and vibrational-rotational dynamics are analyzed and calculated. All physical constants and relaxation rates related to this model are examined. The laser pulse waveform can be calculated when varied laser's parameters. The output power and energy can be obtained from calculated intensity, it can provide theoretical basis for laser design. Theoretical arithmetic shows a good agreement with the experimental result.
The wavelength of CO<sub>2</sub> laser radiation is in the spectral range of 9-11μm. So the rapidly tuning TEA CO<sub>2</sub> laser is an ideal optical source and core parts of laser differential absorption lidar (LDIAL). To expand the spectrum of TEA CO<sub>2</sub> laser and the amount of the atmospheric gases controllable by the LDIAL, laser spectrum of carbon-13 oxygen-16 isotopic species of carbon dioxide is investigated. The spectroscopic constants and wavelength of the two laser band 00011-10001 and 00011-10002 are calculated. Using the spectrum analyzer the spectrum of the TEA CO<sub>2</sub> laser in which <sup>13</sup>C<sup>16</sup>0<sub>2</sub> is used as working gas is obtained. The used laser is a rapidly tuning miniature TEA CO<sub>2</sub> laser. The cavity of the TEA CO<sub>2</sub> laser is 200 mm in diameter and 400 mm in length. The main electrodes are a pair of Chang's aluminum electrodes. Tuning mechanism consists of diffraction grating, trigger controller and high frequency stepping motor. The experimental wavelengths are in good agreement with the calculated data. Compared with common C0<sub>2</sub>, the emission line range of <sup>13</sup>C<sup>16</sup>0<sub>2</sub> is expanded toward the longer wavelength, the longest wavelength of the TEA <sup>13</sup>C<sup>16</sup>0<sub>2</sub> laser is 11.347 μm.
Mie theory is used to study the influence of organic film coatings for bubbles on optical scattering properties of ship wakes. The influence of organic film coatings on the normalized volume scattering function of single bubble is researched. Based on the fractal data of ship wakes, analysis and comparison are made on the scattering properties of clean and coated bubbles, including the normalized volume scattering function, scattering coefficient, backscattering coefficient and backscattering ratio. Organic film coatings have little influence on the critical angle scattering. Contributions of the organic film coatings to the scattering properties of ship wakes relates to the thickness and refractive index of them, in addition, the normalized volume scattering function also relates to the scattering angle. Scattering properties of ship wakes are of importance to wake homing and optical remote sensing of ocean.
In the present work, directed toward using differential absorption lidar (DIAL) for measuring concentrations of pollutant gases, a galvanometer-driven mirror to scan a fixed diffractive grating for rapidly tuning a TEA CO<sub>2</sub> laser is reported. It is well known that the ground- or air-basing DIAL is an effective tool for remote measurement of pollutant gaseous concentration of the atmosphere over large areas. It has, practically in real time, the ability to remotely detect various gas concentrations in the atmosphere, because many pollutant gases have strong absorption lines within the spectral range of CO<sub>2</sub> laser wavelength tuning. In addition, the radiation of CO<sub>2</sub> laser is safe for the human eye and is well distributed in the atmosphere, coinciding with the “transparency window” of the atmosphere. Therefore the wavelength tunable TEA CO<sub>2</sub> laser is an ideal optical source for DIAL. The tuning is performed by generating and applying appropriate signals to the galvanometer, which rotated a silver mirror in order to scan the fixed grating. The device is driven by a programmable signal generator with resolution sufficient to rotate the mirror in discrete intervals as small as 70μrad, which is more than sufficient to find the optimum position for any lasing transition.
Due to their interesting physical and chemical parameters, tunable transversely excited atmospheric-pressure(TEA) CO<sub>2</sub> lasers are widely utilized in scientific and industrial applications. The CO<sub>2</sub> differential absorption lidar (DIAL) is an effective tool for remote measurement of pollutant gaseous concentration of the atmosphere over large areas. Many pollutant gases have strong absorption lines within the spectral range of CO<sub>2</sub> laser wavelength tuning. In addition, the radiation of CO<sub>2</sub> laser is well distributed in the atmosphere, coinciding with the "transparency window" of the atmosphere. Therefore the wavelength tunable TEA CO2 laser is an ideal optical source for DIAL. Most existing instruments for measuring the laser wavelength are only suitable for the measurement of continuous wave and stable frequency output. With the attempt of measuring the wavelength of pulsed TEA CO<sub>2</sub> laser, an experimental setup is established which consists of two main portions, namely auto-scanning grating monochromator as the color dispersion system and Boxcar integrator. In the experiment of tuning TEA CO<sub>2</sub> laser, the wavelength of CO<sub>2</sub> laser is observed and measured by means of integrating method. The accuracy of measurement in the mid-infrared region attains 1nm.
As it is known well, using of frequency doubling in differential absorption CO<sub>2</sub> laser lidars increases the number of atmospheric gases under the control. Additional improvement in potential and gas analyses accuracy, technical and exploitation parameters has to be waited for with design of frequency doublers with more efficient nonlinear crystals. In this work for the first time detailed investigation results are represented on physial properties of new mixed nonlinear crystals grown in accordance with diagram HgGa<sub>2</sub>S<sub>4</sub>:CdGa<sub>2</sub>S<sub>4</sub>→Hg<sub>1-x</sub>Cd<sub>x</sub>Ga<sub>2</sub>S<sub>4</sub>, phase-matching and potential efficiencies of second harmonic generation, so as on results of experimental investigation of TEA and mini TEA CO<sub>2</sub> laser frequency doubling with it use. In spite of two time lower nonlinear susceptibility coefficients of both parent crystals in comparison with most efficient middle IR crystals high efficiency of frequency doubling is fixed in mixed crystals at room temperature. It is tree time in comparison with frequency doubling with, for example, popular ZnGeP<sub>2</sub> and 5.5 time with AgGaSe<sub>2</sub>. These advantages are reached because realization of optimal non-critical phase-matching by choose of mixing ratio x=0.5, so as 2.3 time higher damage threshold, lower phonon absorption at CO<sub>2</sub> laser wavelengths and lower meanings of refractive indexes at fundamental and second harmonic wavelengths. Exploitation parameters of mixed Hg<sub>1-x</sub>Cd<sub>x</sub>Ga<sub>2</sub>S<sub>4</sub> crystal doublers are not worse than parameters of doublers with well-known crystals.
3~5um mid-infrared laser displaying good atmospheric transmitting properties is mostly used as laser source, in many applications such as remote sensing for air pollution determining. And it is usually obtainable in Second harmonic generation (SHG) in CO<sub>2</sub> laser. In the course of investigation, a homemade nonlinear optical crystal AgGaSe<sub>2</sub>, of the size 7×8×12mm<sup>3</sup>, was used for SHG in tunable TEA CO<sub>2</sub> laser with different wavelengths. And, 12 coherent laser sources in 3~5μm from CO<sub>2</sub> spectrum region 10.6μm~9.2μm were obtained. In our results, phase-matching angles aqre in good accordance with the crystal's cutting. Theory calculating on conversion was made as well, to compare with experimental data which present changes of energy conversion under pump's rising. And in the interest of enhancing energy conversion by means of peaking pulse through cutting tail, a plasma shutter, argon charged in body under normal air pressure, was effectively arranged in experiment. As a result, about 50nS width peak pulse was generated, and up to 10% energy conversion (2mJ, 5.3μm) was achieved against 1% without shutter, both pumping in 10P(20) line.
In the present work, directed toward using differential absorption lidar (DIAL) for measuring concentrations of pollutant gases, a monolithic microprocessor-controlled tuning and triggering system for rapidly tuning a TEA C02 laser is reported. It is shown that it is possible to utilize a high frequency stepping motor and a diffraction grating to rapidly select wavelength over rotational transitions in the 9.2-10.8 jtm region of the laser spectrum. The tuning is performed by applying appropriate signals to the stepping motor, which is coupled to the grating via a precision gear box. The microprocessor controls motion of the motor which rotates the correct angle for a given wavelength together with the grating. Many of pollutants have strong absorption lines in the 9-11 im region, therefore the wavelength tunable transversely excited atmospheric-pressure (TEA) CO2 laser becomes an ideal optical source for DIAL.
Second harmonic generation of tunable TEA CO2 laser has the greatest potential for providing the coherent radiation in the wave range of 3~5µm which has many virtues. But the low conversion efficiency has restricted its wide application. In order to raise the conversion efficiency by lengthening the nonlinear effecting extent, two crystals were used which were placed in symmetrical position. In this way the beam can be compressed at the same time. In our experiment, the conversion efficiency up to I .5 times that of one crystal was achieved. Another factor that can affect the conversion efficiency was the quality of the pumping laser, so a plasma shutter was used to shape the laser pulse. Through the shutter the pulse energy was decreased but the pulse width was compressed accordingly, so the pump power was enhanced. By means of this, the conversion efficiency was improved from less than 2% to 12.9% and the highest output energy of 1 .44mJ has been achieved.
Two types of plasma shutters which can achieve pulse shaping of transversely excited atmospheric-pressure (TEA) CO2 laser are presented. We have designed two optical devices, which are plasma shutter and laser triggering spark gas (LTSG). The pulse forming network circuit used for precise triggering control is designed. In experiment, optical triggering gas free-breakdown plasma shutter and electrical triggering plasma shutter controlled via LTSG are researched for pulse shaping of the TEA CO2 laser. The collimated laser beam is focused at the center of two ZnSe lenses, producing an intensity of approximately 7x 1O'°W/cm2. In order to optimize truncated laser pulses, some operating parameters which include gas types filled in plasma shutter, gas pressure, LTSG 's voltage, and so on, are investigated via experiments. Using this technique, the nitrogen "tail" of the TEA CO2 laser pulse can be clipped, thus shortening the output laser pulse from the duration ~60ns to ~30ns.
In this paper, it is reported that diamond films have been synthesized by the Laser Assisted Chemical Vapor Deposition (LACVD) method using the mixture of acetone and hydrogen. The XeCl excimer laser with a wavelength of 308 nm has been utilized as photo-dissociation energy source for carbohydrate, and H<SUB>2</SUB> has been predissociated by hot filament at the temperature of 2000 degrees Celsius. P-type silicone was employed as substrate, which temperature was controlled at about 800 degrees Celsius. The specimens deposited by the method of LACVD were analyzed and evaluated by Raman spectroscopy and scanning electronics microscopy (SEM) accordingly. A character peak of diamond films at 1332 cm<SUP>-1</SUP> can be observed from Raman spectrum. The experimental result have shown that a high-quality diamond film can be obtained.
In our work, the design and performance of a new kind TEA CO<SUB>2</SUB> laser is reported. It was preionized by ultraviolet (UV) from surface corona discharge. A BN ceramic structure was employed as an assembly of resonators. The output energy of 143 mJ, the pulse duration of 50 ns, the transverse mode of TEM<SUB>00</SUB>, the repetition-rate of 50 Hz, the divergence of only 4 mrad was obtained. Comparing with UV bare-spark- preionized (BSP) TEA CO<SUB>2</SUB> lasers, it was found that (1) the uniform of the main electrode discharge was improved, (2) the repetition-rate was improved from 30 Hz to 50 Hz, (3) the input energy was four times lower than that of BSP TEA CO<SUB>2</SUB> laser under the same output energy, (4) the lifetime reached 10<SUP>6</SUP> pulse, (5) the stability of resonator was improved, the output energy eliminated only 14% after 3.5 hours operation. The performance was improved because the intrinsic efficiency of surface corona preionization was four times higher than that of BSP one, the corona discharge was very uniform and photodissociation processes involved in BSP were avoided. The extremely low thermal-expansion of BN minimized the misalignment, so the high reliability can be obtained.