In this paper, a novel chlorophyll measurement system based on Y-type fiber is designed, and the chlorophyll value is obtained according to the intensity ratio of laser fluorescence-Raman signal produced by laser incident into water. In the system, a 405nm semiconductor laser is used as the light source. The laser is coupled into the delivering port of Y-type fiber and then transmitted into water. The generated scattered light, water Raman light and corresponding fluorescence are received and transmitted into spectrometer through the detecting port of Y-type fiber, and the chlorophyll can be obtained by analyzing the laser fluorescence-Raman ratio of water spectra. In experiment, we detect the chlorophyll standard solutions under a range of concentrations, and establish the correlation between chlorophyll concentration and fluorescence-Raman ratio (r2=0.98). In addition, the chlorophyll of natural water sample is measured with laser spectroscopy, the results of which are consistent with chlorophyll values obtained by traditional spectrophotometry. The experimental results prove that the chlorophyll detection method proposed in this paper has the advantages of high sensitivity, high precision, high detection speed and simplicity, which can be widely used in various water areas for real-time chlorophyll detection.
Fluorescence spectroscopy has received attention in the water quality monitoring, as it is a rapid, reagentless technique that requires no sample preparation prior to analysis. It has been investigated as a monitoring tool for a range of applications including water quality and pollution monitoring in marine, rivers and lakes. The permanganate index (CODmn) can reflect the degree of water damage by organic pollutants, and is an important indicator for water environment protection and marine monitoring. In this paper, we present a compact handheld fluorescence spectrometer for water CODmn measurement. The semiconductor laser, spectroscopic unit and detection unit are integrated in the spectrometer, its actual size is about 100mm×60mm×25mm. The spectrometer covers the wavelength range of 400-760 nm, with spectral resolution of 2 nm. The semiconductor laser emitting at 405 nm is employed as the excitation source, which is controlled by the computer. The laser is incident into the water in test bottle at a certain angle in order to avoid the interference come from the bottle wall. The scattered light, water Raman light and organic matter fluorescence excited by the laser can be received by the spectrometer. The CODmn can be obtained according to the method of intensity ratio of laser Fluorescence-Raman signal proposed by us. In the experiment, water samples collected from 9 different sites of Sow River at Weihai are tested by using our designed handheld fluorescence spectrometer. The CODmn can be achieved by the computer analyzing the spectral curve. In addition, we also measured the 9 water samples by chemical method, and the obtained permanganate index compared very well to the values by using our designed spectrometer: a significant relationship (R2=0.941) is identified between the two methods. The experimental results indicate that our designed spectrometer has the advantages of small size, high sensitivity and high detection speed, which is promising for CODmn monitoring in many water areas.
A portable laser induced fluorescence (LIF) lidar system (total weight about 5 kg) was developed for real-time remote sensing oil in aquatic environment. LIF lidar consists of 405nm semiconductor laser, receiving telescope, double Amici prism spectrometer and ICCD detecting system, which can detect fluorescence signal in the spectral range of 400-750 nm. In the laboratory, the fluorescence spectra of water samples with different oil concentration were investigated. The contents of oil were calculated using the ratio between fluorescence and intensity. The LIF lidar system has the advantages of compact configuration and low cost, which is promising for monitoring water quality rapidly. The portable system can be installed on small aircrafts, unmanned aerial vehicles, ships, and shore platform for remote monitoring aquatic environments.
Laser induced breakdown spectroscopy (LIBS) is a kind of laser ablation spectrum analysis technology, which has the advantages of small sample damage, fast detection speed and simultaneous detection of multiple elements. In this paper, a LIBS system based on passive Q-switched laser is designed, which is used to carry out marine heavy metal detection research. Aiming at the two or more laser pulses that the laser may generate in a single pumping cycle, a laser pulse control module is designed in this paper to analyze and judge the number of laser pulses, and obtain good experimental results. Using this LIBS system to output single-pulse and double-pulse lasers to detect samples of seawater and shells in different regions, we can detect the presence of characteristic spectral lines of elements such as Na, Mg, Ga and other elements in seawater. At the same time, the characteristic spectra of Cu, Al and some other elements are found in the shell samples, which suggest that there are heavy metal pollution components in the shells.
In this paper, a mode-locked Ytterbium-doped fiber laser based on nonlinear optical loop mirror (NOLM) is proposed. The laser generates a wide-spectrum dissipative soliton resonance mode-locked pulse with strong stimulated Raman scattering. The fiber laser is pumped forward, and the fiber ring cavity contains double-cladding Yb-doped fiber, output coupler, polarization controller, polarization independent isolator and other elements. NOLM is connected with the ring cavity by through a 3dB beam splitter and 25m single-mode fiber. The total length of the eight-shape cavity laser is about 60meters. By adjusting the intra-cavity polarization controller, a stable dissipative soliton resonance mode-locked spike pulse can be achieved. The repetition frequency of the pulse train is 3.44MHz, which is consistent with the cavity length. The 3dB bandwidth of the spectrum reaches 70.6nm, and the 10dB bandwidth is close to 147.11nm. In this experiment, dissipative soliton resonance mode-locked pulses with wide spectrum and high pulse energy are realized by a traditional mode-locking method, which has wide application in many fields such as laser spectral detection and terahertz wave generation.
We demonstrated a multi-dark soliton train generated from self-mode-locking ultra-long ring cavity fiber laser. The fiber laser used 10m double-clad Yb-doped fiber as gain medium, and used a polarization independent isolator to ensure the light propagation in one direction. The ring cavity of the laser was designed without any intra-cavity polarization controlling component. The cavity length is 1300 meters by insetting single mode fiber. When the pump power was increased to 2.75W, the multi-dark soliton trains were obtained. The stable pulse train has a repetition rate of 153.9 kHz corresponding to the cavity length. The number of sub-pulse continues to decrease during the increase of the incident pumping power until 3.39W. Stable three peaks appear in the spectra of our fiber laser due to the absence of the polarization controller in the cavity. The maximum peak wavelength locates around 1083.9nm with the 3dB bandwidth of 1.4nm. There are two sidebands with the central wavelength of 1086.3nm and 1090.1nm with a lower intensity. The occurrence of multi-dark soliton pulses train is relevant to the self-mode-locked operation at the cavity with a large amount of normal dispersion and accumulated nonlinearity.
KEYWORDS: Imaging systems, LIDAR, Analog electronics, 3D image processing, 3D acquisition, Image processing, 3D image reconstruction, Signal processing, Control systems, Process control
A precise delay system for a streak tube imaging lidar (STIL) is developed. Two delay schemes are designed that are suitable for long- and short-distance lidar imaging. The digital scheme delay can reach 100 μs, and its precision is <6 ns; the analog scheme delay can reach 1200 ns and its precision is <1 ns. Using the STIL system, three-dimensional (3-D) imaging experiments are carried out on land targets at about 2.3-km range and underwater targets at about 25-m range. The experimental results show that the designed delay device can produce precise delay times and effectively verify the 3-D imaging quality of the STIL. This device also has the advantages of stable operation, being more compact, and requiring less power than existing instruments.
A high frame rate streak tube imaging lidar (STIL) for real-time 3D imaging of underwater targets is presented in this paper. The system uses 532nm pulse laser as the light source, the maximum repetition rate is 120Hz, and the pulse width is 8ns. LabVIEW platform is used in the system, the system control, synchronous image acquisition, 3D data processing and display are realized through PC. 3D imaging experiment of underwater target is carried out in a flume with attenuation coefficient of 0.2, and the images of different depth and different material targets are obtained, the imaging frame rate is 100Hz, and the maximum detection depth is 31m. For an underwater target with a distance of 22m, the high resolution 3D image real-time acquisition is realized with range resolution of 1cm and space resolution of 0.3cm, the spatial relationship of the targets can be clearly identified by the image. The experimental results show that STIL has a good application prospect in underwater terrain detection, underwater search and rescue, and other fields.
Laser Induce Fluorescence (LIF) is a widely used new telemetry technology. It obtains information about oil spill and oil film thickness by analyzing the characteristics of stimulated fluorescence and has an important application in the field of rapid analysis of water composition. A set of LIF detection system for marine oil pollution is designed in this paper, which uses 355nm high-energy pulsed laser as the excitation light source. A high-sensitivity image intensifier is used in the detector. The upper machine sends a digital signal through a serial port to achieve nanoseconds range-gated width control for image intensifier. The target fluorescence spectrum image is displayed on the image intensifier by adjusting the delay time and the width of the pulse signal. The spectral image is coupled to CCD by lens imaging to achieve spectral display and data analysis function by computer. The system is used to detect the surface of the floating oil film in the distance of 25m to obtain the fluorescence spectra of different oil products respectively. The fluorescence spectra of oil products are obvious. The experimental results show that the system can realize high-precision long-range fluorescence detection and reflect the fluorescence characteristics of the target accurately, with broad application prospects in marine oil pollution identification and oil film thickness detection.
Method of homogenization of CO2 laser heating by means of metal gauze is researched theoretically and experimentally. Distribution of light-field of expanded beam passing through metal gauze was numerically calculated with diffractive optical theory and the conclusion is that method is effective, with comparing the results to the situation without metal gauze. Experimentally, using the 30W DC discharge laser as source and enlarging beam by concave lens, with and without metal gauze, beam intensity distributions in thermal paper were compared, meanwhile the experiments based on thermal imager were performed. The experimental result was compatible with theoretical calculation, and all these show that the homogeneity of CO2 laser heating could be enhanced by metal gauze.
This paper presents a kind of miniature handheld laser fluorescence spectrometer, which integrates a laser emission system, a spectroscopic system, and a detection system into a volume of 100×50×20 mm3. A universal serial bus interface is connected to PC for data processing and spectrum display. The emitted laser wavelength is 405 nm. A spectral range is 400 to 760 nm and 2-nm optical resolution has been achieved. This spectrometer has the advantages of compact structure, small volume, high sensitivity, and low cost.
We present an optical receiving system for LIF lidar using a direct view spectrometer based on holographic grating prism. The proposed receiving optical system consists of receiving telescope, slit, collimating lens, holographic grating prism, objective lens and ICCD camera. The receiving optical system based on this dispersion structure can not only reduces the optical distortion to offer a high optical efficiency, but also has a more compact structure which is very suitable for spectral dispersion of remote target. The system adopted an intensifier coupled a CCD to make up an ICCD camera. Based on real-time background subtraction algorithm, 60fps fluorescence spectrum can be obtained in real time. System validation experiment uses a semiconductor laser as excitation source to illuminate oil target to radiate fluorescence at a distance of 30 m. The fluorescent signal is received by the set up LIF lidar receiving optical system, and clear spectrum image is obtained. The designed in-line, direct view configuration holographic grating prism spectrometer owns the advantages of high light throughput, less optical distortions, compact structure, small volume and easy operation, which make a practical portable receiving optical system.
In this paper, we present a prism spectrometer that exploits a double Amici prism dispersion structure. The system consists of a slit, a collimating lens, a double Amici prism, an imaging lens and a CCD. The incident light enter into slit, and then is paralleled by a collimating lens to the double Amici prism. The double Amici prism is used to realize spectral dispersion. The dispersed light is collected by an imaging lens and image on the photosensitive surface of the CCD. The dispersion resolution is theoretical analyzed from the ray tracing point of view. In addition, the imaging position on CCD element at different wavelength is presented according to nonlinear curve of dispersion. The designed prism spectrometer can obtain a high light throughput and less optical distortion spectrum in the spectral range of 370-700nm. In experiment, we measured the spectral resolution of the designed prism spectrometer at five wavelength used a grating monochromator. The designed in-line, direct view configuration prism spectrometer owns the advantages of high light throughput, less optical distortions, compact structure, small volume and easy operation, which has important role in application of laser spectral measurement especially laser remote sensing spectral detection.
A method using rotating Fabry–Perot (FP) mirror to measure CO2 laser wavelength was developed. The variation of FP transmittance changing with laser incident angle was calculated theoretically and the variation curve was given. The calculation illustrates that the variation of FP reflectance with incident angle 0 to 30 deg has little effect on the transmittance of FP. In the experiments, the CO2 laser transmittance variation of FP was measured at a wavelength of 9.27 μm. To improve the measurement precision of the laser wavelength, the method using the centrosymmetric peaks of FP transmittance curve in the range from −20 to +20 deg of laser incident angle was proposed. The precision of the measurement is about 0.01 μm. The experiment result is consistent with theoretical analysis, which demonstrates the feasibility of the laser wavelength measurement using rotating FP method.
Soliton decay and dispersive wave generation in photonic crystal fiber (PCF) are investigated. Grating-eliminated no-nonsense observation of ultrafast incident laser light e-fields technique is used to measure the temporal and spectral evolutions of soliton. Soliton decay and dispersive wave generation are clearly demonstrated. At low pump power, there is only soliton decay and no dispersive wave generated because all frequencies are in the anomalous dispersion region of the PCF, and the soliton spectrum does not touch the spectrum of linear dispersive waves. At relatively high power, a part of the soliton energy is transferred from soliton to a dispersive wave and falls on the blue side of the original carrier frequency of the incident pulse.
To provide high efficient pumping source for THz laser, we designed a new active frequency stabilized system for gain switched RF CO2 laser. According to our theoretical analysis and experimental study, the pulse setup time is varied for different output power. The pulse setup time is shortest when the output power is highest for a pulse laser. It is equivalent to stabilize the laser frequency and power if the pulse setup time is locked in the center of laser gain curve. By the method of adjusting the pulse setup time, we have stabilized a pulse rf excited CO2 laser at the center of the laser gain curve. The frequency stability is estimated to be less than 5MHz.
KEYWORDS: Solid state lasers, Solids, Near field, Near field optics, High power lasers, Thermal effects, Gas lasers, Lamps, Laser development, Solid state physics
We designed a new solid-state laser with the construction of radial slab array. Three kinds of gain
distributions are considered according to different pumping structure. The numerical calculated results show
that this kind of laser can output high beam quality laser both coherent and incoherent conditions. It is
prospective to be a new research direction for high power, high beam quality, compact and scalable solid
laser.
KEYWORDS: Solids, Near field optics, Carbon dioxide lasers, High power lasers, Near field, Semiconductor lasers, Laser applications, Thermal effects, Mirrors, Laser development
Optic field intensities of double and triple parallel slabs solid laser are numerically calculated. The results show that high beam qualities are difficult to obtain no matter coherent or incoherent output. In order to obtain high beam quality for mult-slab solid laser, we designed a new solid laser construction of radial slabs array according to the present condition for solid and RF excited radial array CO2 gas laser. The numerical calculated results show that this kind of laser can output high beam quality laser both coherent and incoherent cases. It is prospective to be a new research direction for high power, high beam quality, compact and scale solid laser.
A tunable electro-optically Q-switched rf-excited partial Z-fold CO2 waveguide laser with two channels has been designed. Q-switched pulses were obtained from the partial Z-fold channel. The peak power is 730 W, and the pulse width is 150 ns. Cw laser output was obtained from the other channel, which can be tuned by a grating. A stable pulse heterodyne waveform and its Fourier transform (frequency spectrum) were also observed.
An experimental investigation of a pulsed electrooptically Q-switched radio-frequency partial Z-fold waveguide CO2 laser with two channels is presented. The heterodyne frequency stability is analyzed in theory. Q-switched pulses are obtained from the partial Z-fold channel. The peak power is 730W and the pulse width is 150 ns. CW laser can output from the single channel. The laser output directions are opposite.
Two kinds of Q-switched RF excited waveguide CO2 lasers using Q-switching and FM crystal respectively are studied. They are used to detect laser return signal from targets of 20m distances without using telescope in experiment. The waveform of pulse laser heterodyne and its frequency spectrum of Fourier transform scattered from targets are studied. According to radar distance equation, the laser can be applied to detect targets of 5Km distances using telescope.
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