S. Byron, P. Cassady, T. Znotins, D. Quimby, S. Moody
For many applications that utilize single frequency output of pulsed CO2 lasers, the shift in frequency during the pulse must be minimized. For example, in CO2 coherent Doppler lidar backscatter measurements of atmospheric wind speeds, the intrapulse chirp must be less than 200 kHz in order to achieve a wind speed resolution of 1 m/sec.1 Experimental studies in CO2 hybrid TEA lasers show a characteristic U-shape curve of frequency versus time, first falling during the early part of the pulse and then rising throughout the remainder of the pulse. Measured values of chirp range from 0.5 to 5 MHz for 3 μsec duration pulses. Analysis and experiments by Willetts and Harris2 have shown that the early chirp is due to decay of the plasma electron density in the laser gas and the late chirp is due to the gas density decrease near the optical axis of the cavity caused by nonuniform gas heating induced by the radial intensity profile of the laser mode structure.
{"title":"Chirp Analysis for Pulsed CO2 Laser Oscillators","authors":"S. Byron, P. Cassady, T. Znotins, D. Quimby, S. Moody","doi":"10.1364/clr.1983.tud4","DOIUrl":"https://doi.org/10.1364/clr.1983.tud4","url":null,"abstract":"For many applications that utilize single frequency output of pulsed CO2 lasers, the shift in frequency during the pulse must be minimized. For example, in CO2 coherent Doppler lidar backscatter measurements of atmospheric wind speeds, the intrapulse chirp must be less than 200 kHz in order to achieve a wind speed resolution of 1 m/sec.1 Experimental studies in CO2 hybrid TEA lasers show a characteristic U-shape curve of frequency versus time, first falling during the early part of the pulse and then rising throughout the remainder of the pulse. Measured values of chirp range from 0.5 to 5 MHz for 3 μsec duration pulses. Analysis and experiments by Willetts and Harris2 have shown that the early chirp is due to decay of the plasma electron density in the laser gas and the late chirp is due to the gas density decrease near the optical axis of the cavity caused by nonuniform gas heating induced by the radial intensity profile of the laser mode structure.","PeriodicalId":408663,"journal":{"name":"2nd Topical Meeting on Coherent Laser Radar: Technology and Applications","volume":"60 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116586660","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pulsed coherent Doppler lidars operating at CO2 wavelengths have shown considerable promise for remote measurement of wind velocities. Range and data rates are limited at present by the single pulse energy and repetition rates available from current generation pulsed CO2 lasers. Recently, we have undertaken the development of a laser system for pulsed lidar application which is capable of producing 2 Joule pulses at a 50 Hz repetition rate. This laser will be installed in the NOAA ground-based Doppler lidar system.1 The laser system is designed to be tunable over a wide range of lines, including the 9 μm band of CO2, and to allow pulse length variability, which is relevant to DIAL applications. The laser system includes a cw local oscillator which is frequency locked to the transmitted pulse for use in the heterodyne receiver. Table 1 summarizes the specifications of the system under construction.
{"title":"100 Watt Average Power CO2 Laser System for Pulsed Coherent Lidar Applications","authors":"S. Moody, T. Znotins, S. Byron","doi":"10.1364/clr.1983.mc2","DOIUrl":"https://doi.org/10.1364/clr.1983.mc2","url":null,"abstract":"Pulsed coherent Doppler lidars operating at CO2 wavelengths have shown considerable promise for remote measurement of wind velocities. Range and data rates are limited at present by the single pulse energy and repetition rates available from current generation pulsed CO2 lasers. Recently, we have undertaken the development of a laser system for pulsed lidar application which is capable of producing 2 Joule pulses at a 50 Hz repetition rate. This laser will be installed in the NOAA ground-based Doppler lidar system.1 The laser system is designed to be tunable over a wide range of lines, including the 9 μm band of CO2, and to allow pulse length variability, which is relevant to DIAL applications. The laser system includes a cw local oscillator which is frequency locked to the transmitted pulse for use in the heterodyne receiver. Table 1 summarizes the specifications of the system under construction.","PeriodicalId":408663,"journal":{"name":"2nd Topical Meeting on Coherent Laser Radar: Technology and Applications","volume":"17 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124967221","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Mode selection in a TEA-CO2 laser cavity through the use of injection techniques provides high peak power single-longitudinal-mode (SLM) pulses with relatively low intensities of injected radiation. Provided the selected mode is near the center of the pressure-broadened TEA-CO2 gain transition, and the frequency proximity requirements are met, as little as 10 μW of injected power is sufficient to effectively produce a single-frequency pulse with peak power of several MW [1]. However, if tunable pulses are desired, the requirements for mode selection as the frequency of the injected radiation is tuned away from the CO2 transition center frequency become more demanding. An analytical treatment of the coupled rate equation for the molecular population densities and for the photon densities yields an expression for the "mode selection time", or the time during which the photon flux in the favored mode is a large fraction (e.g., >90%) of the total photon flux [2]. This expression is valid for values of molecular resonance detuning smaller than the pressure-broadened halfwidth (ΔνL) of the transition.
{"title":"Requirements for Tunable Mode and Line Selection by Injection in a TEA-CO2 Laser","authors":"R. Menzies, P. Flamant, M. Kavaya","doi":"10.1364/clr.1983.tud2","DOIUrl":"https://doi.org/10.1364/clr.1983.tud2","url":null,"abstract":"Mode selection in a TEA-CO2 laser cavity through the use of injection techniques provides high peak power single-longitudinal-mode (SLM) pulses with relatively low intensities of injected radiation. Provided the selected mode is near the center of the pressure-broadened TEA-CO2 gain transition, and the frequency proximity requirements are met, as little as 10 μW of injected power is sufficient to effectively produce a single-frequency pulse with peak power of several MW [1]. However, if tunable pulses are desired, the requirements for mode selection as the frequency of the injected radiation is tuned away from the CO2 transition center frequency become more demanding. An analytical treatment of the coupled rate equation for the molecular population densities and for the photon densities yields an expression for the \"mode selection time\", or the time during which the photon flux in the favored mode is a large fraction (e.g., >90%) of the total photon flux [2]. This expression is valid for values of molecular resonance detuning smaller than the pressure-broadened halfwidth (ΔνL) of the transition.","PeriodicalId":408663,"journal":{"name":"2nd Topical Meeting on Coherent Laser Radar: Technology and Applications","volume":"7 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122699107","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In order to meet societal needs for improved weather forecasts, old and new technology must be blended to provide a more detailed and spatially broader view of the atmosphere. Advancing technology, and its associated needs for efficiency, have increased demands for weather information at both short ranges (1-2 days) and extended ranges (1 week-1 month). Over the past two decades the introduction of improved mathematical techniques and electronic technology have allowed a more precise application of the laws of physics to the atmosphere, leading to significant increases in prediction accuracy. There is ample evidence that further advances in predictive ability can be achieved if inherent approximations remaining in the numerical weather prediction (NWP) system are made with more precision.
{"title":"Data Requirements for an Operational Weather Prediction System in the 1990's","authors":"J. B. Hovermale","doi":"10.1364/clr.1983.mb1","DOIUrl":"https://doi.org/10.1364/clr.1983.mb1","url":null,"abstract":"In order to meet societal needs for improved weather forecasts, old and new technology must be blended to provide a more detailed and spatially broader view of the atmosphere. Advancing technology, and its associated needs for efficiency, have increased demands for weather information at both short ranges (1-2 days) and extended ranges (1 week-1 month). Over the past two decades the introduction of improved mathematical techniques and electronic technology have allowed a more precise application of the laws of physics to the atmosphere, leading to significant increases in prediction accuracy. There is ample evidence that further advances in predictive ability can be achieved if inherent approximations remaining in the numerical weather prediction (NWP) system are made with more precision.","PeriodicalId":408663,"journal":{"name":"2nd Topical Meeting on Coherent Laser Radar: Technology and Applications","volume":"10 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127177230","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
It is well known that small quantities of stray light reflected back into a laser cavity can produce large perturbations in the laser characteristics. To the best of our knowledge, however, no one has recognized that this effect can be used as a sensitive detection process for making Doppler velocity measurements. This technique has the added featurs that the critical beamsplitter alignment requirements of conventional laser Doppler velocimetry have been eliminated by eliminating the beamsplitter. We report here a demonstration using a CO2 laser and a rotating disk target.
{"title":"Laser Doppler Velocimetry by Backscatter Modulation of the Source","authors":"J. Churnside","doi":"10.1364/clr.1983.mc5","DOIUrl":"https://doi.org/10.1364/clr.1983.mc5","url":null,"abstract":"It is well known that small quantities of stray light reflected back into a laser cavity can produce large perturbations in the laser characteristics. To the best of our knowledge, however, no one has recognized that this effect can be used as a sensitive detection process for making Doppler velocity measurements. This technique has the added featurs that the critical beamsplitter alignment requirements of conventional laser Doppler velocimetry have been eliminated by eliminating the beamsplitter. We report here a demonstration using a CO2 laser and a rotating disk target.","PeriodicalId":408663,"journal":{"name":"2nd Topical Meeting on Coherent Laser Radar: Technology and Applications","volume":"5 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128578750","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Observations of the atmosphere and its underlying surfaces (land and oceans) by space-based sensors have already made significant contributions to our understanding of atmospheric behavior. However, with one or two exceptions, these sensors have been passive in design and have therefore been subject not only to restrictive limitations in horizontal and vertical resolution, but in accuracy. Inversion schemes necessary to convert the measured radiances to a useful atmospheric parameter, a temperature profile for example, contribute to further degradation in the accuracy of the measurement.
{"title":"NASA Research Requirements for Atmospheric Observations","authors":"J. Theon","doi":"10.1364/clr.1983.mb3","DOIUrl":"https://doi.org/10.1364/clr.1983.mb3","url":null,"abstract":"Observations of the atmosphere and its underlying surfaces (land and oceans) by space-based sensors have already made significant contributions to our understanding of atmospheric behavior. However, with one or two exceptions, these sensors have been passive in design and have therefore been subject not only to restrictive limitations in horizontal and vertical resolution, but in accuracy. Inversion schemes necessary to convert the measured radiances to a useful atmospheric parameter, a temperature profile for example, contribute to further degradation in the accuracy of the measurement.","PeriodicalId":408663,"journal":{"name":"2nd Topical Meeting on Coherent Laser Radar: Technology and Applications","volume":"83 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115315439","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Traditional visible lidars are far from diffraction limited. Transmitter and receiver are not exactly matched. A diffraction limited system provides for a lower background and a return signal better suited for analysis by high resolution interferometers or even heterodyning. A diffraction limited system will in general have a range weighting different from the simple 1/z2 -dependence. Strong focusing may be encountered. They are also considered to be much more susceptible to optical refractive turbulence.
{"title":"Experimental Verification of a Diffraction Limited Lidar","authors":"L. Lading, A. S. Jensen","doi":"10.1364/clr.1983.tub6","DOIUrl":"https://doi.org/10.1364/clr.1983.tub6","url":null,"abstract":"Traditional visible lidars are far from diffraction limited. Transmitter and receiver are not exactly matched. A diffraction limited system provides for a lower background and a return signal better suited for analysis by high resolution interferometers or even heterodyning. A diffraction limited system will in general have a range weighting different from the simple 1/z2 -dependence. Strong focusing may be encountered. They are also considered to be much more susceptible to optical refractive turbulence.","PeriodicalId":408663,"journal":{"name":"2nd Topical Meeting on Coherent Laser Radar: Technology and Applications","volume":"63 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124795773","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The sensitivity advantages of coherent detection can potentially be employed to make range-resolved differential absorption lidar (DIAL) measurements of atmospheric species even when transmit pulse energies are relatively low. By operating in a shot-noise-limited mode, coherent lidars often obtain average carrier-to-noise ratios (CNR's) as much as 30 dB higher than would be measured with equivalent direct-detection systems. This apparent advantage in average CNR is at least partially offset by the characteristically large fluctuation in the instantaneous received irradiance due to target speckle effects.1 To measure mean backscattered-signal irradiance accurately, the variance due to these fluctuations must be reduced to an acceptable level by averaging.
{"title":"Coherent Lidar Measurement of Range-Resolved Tropospheric Water Vapor Concentration and Backscattered Signal Statistics","authors":"R. Hardesty","doi":"10.1364/clr.1983.tha4","DOIUrl":"https://doi.org/10.1364/clr.1983.tha4","url":null,"abstract":"The sensitivity advantages of coherent detection can potentially be employed to make range-resolved differential absorption lidar (DIAL) measurements of atmospheric species even when transmit pulse energies are relatively low. By operating in a shot-noise-limited mode, coherent lidars often obtain average carrier-to-noise ratios (CNR's) as much as 30 dB higher than would be measured with equivalent direct-detection systems. This apparent advantage in average CNR is at least partially offset by the characteristically large fluctuation in the instantaneous received irradiance due to target speckle effects.1 To measure mean backscattered-signal irradiance accurately, the variance due to these fluctuations must be reduced to an acceptable level by averaging.","PeriodicalId":408663,"journal":{"name":"2nd Topical Meeting on Coherent Laser Radar: Technology and Applications","volume":"29 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124419094","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A cw heterodyne lidar system operating at 10.6 μm, that determines the concentration of aerosols has been developed and is described with experimental data.
研制了一种工作在10.6 μm波段的连续波外差激光雷达系统，并用实验数据进行了描述。
{"title":"Heterodyne Lidar for Monitoring Aerosols","authors":"W. W. Montgomery","doi":"10.1364/clr.1983.thb7","DOIUrl":"https://doi.org/10.1364/clr.1983.thb7","url":null,"abstract":"A cw heterodyne lidar system operating at 10.6 μm, that determines the concentration of aerosols has been developed and is described with experimental data.","PeriodicalId":408663,"journal":{"name":"2nd Topical Meeting on Coherent Laser Radar: Technology and Applications","volume":"29 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126409163","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Two series of simulation experiments were conducted with the GLAS Fourth Order GCM to assess the information content of different observing systems capabilities to infer atmospheric states. In the first set of experiments, the "natural atmosphere" from which simulated observations were derived is a long integration of the model. In the second set of experiments, simulated observations were extracted from the NMC operational analysis for the FGGE Special Observing Period - 1. In both cases, the observations consisted of complete 3-dimensional fields of either winds, temperatures or surface pressure. These observations were then used to run a 12 hour analysis/forecast cycle and the ability of the observations to infer the other unobserved fields was determined from the (asymptotic) 12 hour forecast errors.
{"title":"GCM Simulation Studies on the Relative Importance of Wind Observing Systems for Numerical Weather Prediction","authors":"M. Halem","doi":"10.1364/clr.1983.tua1","DOIUrl":"https://doi.org/10.1364/clr.1983.tua1","url":null,"abstract":"Two series of simulation experiments were conducted with the GLAS Fourth Order GCM to assess the information content of different observing systems capabilities to infer atmospheric states. In the first set of experiments, the \"natural atmosphere\" from which simulated observations were derived is a long integration of the model. In the second set of experiments, simulated observations were extracted from the NMC operational analysis for the FGGE Special Observing Period - 1. In both cases, the observations consisted of complete 3-dimensional fields of either winds, temperatures or surface pressure. These observations were then used to run a 12 hour analysis/forecast cycle and the ability of the observations to infer the other unobserved fields was determined from the (asymptotic) 12 hour forecast errors.","PeriodicalId":408663,"journal":{"name":"2nd Topical Meeting on Coherent Laser Radar: Technology and Applications","volume":"3 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133709957","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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