JaLCDOI 10.18926/15722
FullText URL Mem_Sch_Eng_OU_13_181.pdf
Author Sano, Hiroya| Koga, Ryuji| Tanada, Yoshihiro| Kosaka, Megumi|
Abstract This report deals with a notion of adjoint spectrum which is applicable to air-pollution monitoring by using pulsed lasers. Both Raman and absorption spectra of multiple gas complex are linear combinations of the spectra, each of which is specific to a gas species and its magnitude is proportional to the density. An extended formulation of the method of least squares is made in terms of a new notion, adjoint spectra, which visualizes the structure of the numerical filter. Applications of the derived numerical filters to the two methods are shown and features are described about the synthesized filters.
Publication Title Memoirs of the School of Engineering, Okayama University
Published Date 1979-03-05
Volume volume13
Start Page 181
End Page 193
ISSN 0475-0071
language 英語
File Version publisher
NAID 120002307476
JaLCDOI 10.18926/15723
FullText URL Mem_Sch_Eng_OU_13_195.pdf
Author Sano, Hiroya| Koga, Ryuji| Tanada Yoshihiro| Kosaka, Megumi|
Abstract The maximally attainable accuracy of an airpollution monitoring system is investigated. The system is composed of a tunable pulsed dye laser as the light source, photodiodes as the opto-electric converter and a low noise electronic signal processor specifically designed by the authors. The extreme value of the accuracy is given in terms of the standard deviation of the attenuation. The value is 3.4×10(-4)[Nep√(pulse number)] for an averaged value for multiple laser shots. Also the wavelength reproduceability of a dye laser was examined, which resulted in that a computer should take a part in the wavelength control in order that this method should be feasible.
Publication Title Memoirs of the School of Engineering, Okayama University
Published Date 1979-03-05
Volume volume13
Start Page 195
End Page 207
ISSN 0475-0071
language 英語
File Version publisher
NAID 120002307857
JaLCDOI 10.18926/15740
FullText URL Mem_Sch_Eng_OU_14_1_55.pdf
Author Koga, Ryuji| Hirao, Keiji| Kosaka, Megumi| Sano, Hiroya|
Abstract An absorption spectrum of γ-0 band of nitric monoxide of very dilute density was taken. An experimental electronic device showed a distinguishing power of 0.01 ppm through 10 m optical pathlength. By the aid of a data processing based on a principle developed by the authors, this sensitivity does not suffer from coexisting sulfur dioxide, which shares the absorption band with the nitric monoxide.
Publication Title Memoirs of the School of Engineering, Okayama University
Published Date 1979-12-01
Volume volume14
Issue issue1
Start Page 55
End Page 60
ISSN 0475-0071
language 英語
File Version publisher
NAID 120002307855
JaLCDOI 10.18926/15741
FullText URL Mem_Sch_Eng_OU_14_2_13.pdf
Author Koga, Ryuji| Ebara, Masami| Kosaka, Megumi| Sano, Hiroya|
Abstract A switch element has been developed so that a kilovolt step voltage should be supplied to a 50Ω transmission line with a subnanosecond rise time. The element is of silicon substrate with high purity and a pair of electrodes is attached by the evaporation process. The switch action is performed by the photoconductivity produced by the laser light pulse. This paper deals with a preliminary analysis, manufacturing processes and experimental results of the optoelectronic switch. A performance of 320V output with less than 4 ns risetime was obtained with sufficient persistence for more than 2×10(5) pulse shots. This switch was successfully applied to an optical waveform monitor for laser light pulses giving a resolution less than 2 ns.
Publication Title Memoirs of the School of Engineering, Okayama University
Published Date 1980-03-01
Volume volume14
Issue issue2
Start Page 13
End Page 22
ISSN 0475-0071
language 英語
File Version publisher
NAID 120002307887
JaLCDOI 10.18926/15756
FullText URL Mem_Sch_Eng_OU_15_1_47.pdf
Author Koga, Ryuji| Nagase, Satoru| Kosaka, Megumi| Sano, Hiroya|
Abstract Basic prohlems are discussed about a local, realtime and very sensitive air-pollution monitoring using a laser diode. The method employs the second derivative spectrometry replacing the incoherent light source and mechanical choppers in a traditional method with the laser diode and a newly developed electronic system. Etalon fringes at this system becomes the dominant noise source and its statistic and dynamical features are to be understood. Numerical examination was done for the optimal width of optical frequency modulation. A very fast measurement of weak absorption spectra became possible by the development of lock-in-amplifiers with finite integration time instead of a low-pass filter. Spectra of methane in 7.6 μm region and a time-dependent spectrum of the etaIon fringe are shown.
Publication Title Memoirs of the School of Engineering, Okayama University
Published Date 1980-11-29
Volume volume15
Issue issue1
Start Page 47
End Page 60
ISSN 0475-0071
language 英語
File Version publisher
NAID 120002307627
JaLCDOI 10.18926/15776
FullText URL Mem_Sch_Eng_OU_15_2_79.pdf
Author Koga, Ryuji| Nagase, Satoru| Kosaka, Megumi| Sano, Hiroya|
Abstract A method to monitor atmospheric gas concentration employing a tunable diode laser is proposed. An apparatus was built and experiments were made. The tunable diode laser employed was of'PbSnTe with its wavenumber about 1200 cm(-1) at a temperature of 77 K. Methane concentration in laboratory atmosphere was measured on the experiments. The inquired gas-density is obtained by a hardwired microcomputer incorporating the measured absorption spectrum over a prescribed range instead of an absorption at a single wavenumber. By this, drift type noises are suppressed. After an analysis based on experimental data, an attainable sensitivity for methane was found to be 1 ppb.m. This value may increase if an etalon fringe interference exists. The natural concentration, about 1 ppm, of atmospheric methane was actually measured with a short optical path of only one meter.
Publication Title Memoirs of the School of Engineering, Okayama University
Published Date 1981-03-30
Volume volume15
Issue issue2
Start Page 79
End Page 92
ISSN 0475-0071
language 英語
File Version publisher
NAID 120002307246
JaLCDOI 10.18926/15416
FullText URL Mem_Fac_Eng_OU_26_1_43.pdf
Author Bouzidi, Moncef| Koga, Ryuji| Wada, Osami| Kagawa, Naoki| Hai Xu| Kosaka, Megumi| Sano HIroya|
Abstract A numerical technique called as "adjoint spectrum" has been proposed by the authors in a previous work. Two applications of it are presented here. It is demonstrated that by generalizing the aspect of adjoint spectrum it becomes possible to measure densities of mixed gases simultaneously. An experimental proof of this has been carried on and simultaneous measurement of densities of both methane and dinitrogen oxide was realized. On the other hand, it is also reported that frequency shifting of spectra, which is a cause of error in spectrometric measurements, can be corrected by exploiting the adjoint spectrum technique in connection with the Taylor expansion. Numerical examples showing the success of this method are reported as well.
Publication Title Memoirs of the Faculty of Engineering, Okayama University
Published Date 1991-11-30
Volume volume26
Issue issue1
Start Page 43
End Page 49
ISSN 0475-0071
language 英語
File Version publisher
NAID 120002307796
JaLCDOI 10.18926/15488
FullText URL Mem_Fac_Eng_OU_25_1_37.pdf
Author Bouzidi, Moncef| Koga, Ryuji| Wada, Osami| Kagawa, Naoki| Hai, Xu| Kosaka, Megumi| Sano, Hiroya|
Abstract Is proposed a tunable diode laser absorption spectrometer system which employs a pulsed current to drive the diode laser still implementing a second-harmonic detection methods enhancing a signal to noise up to 104 times that the case without it. This system affords the lead-salt diode laser a higher operating temperature which allows a more compact deep cooling system. A principle is based on employing a gated integrator between the preamplifier and the lock-in amplifier. Investigations are made on the optimum selection of the gating aperture time interval as determined by response time of the infrared detector and the pulse width of the laser driving current.
Publication Title Memoirs of the Faculty of Engineering, Okayama University
Published Date 1990-12-14
Volume volume25
Issue issue1
Start Page 37
End Page 50
ISSN 0475-0071
language 英語
File Version publisher
NAID 120002307549
JaLCDOI 10.18926/15774
FullText URL Mem_Sch_Eng_OU_18_1_91.pdf
Author Sano, Hiroya| Koga, Ryuji| Kosaka, Megumi| Wake, Ichiro|
Abstract This paper presents an optical-waveform synthesizer as one of the applications of optical bistable devices. This device is advantageous in terms of faster operation in which width of each pulse obtained is down to the order of subnanosecond, because this device employs both GaAs- and Si-optoelectronic switches as photodetector. Optical pulse shaping as a preliminary experiment is also described.
Publication Title Memoirs of the School of Engineering, Okayama University
Published Date 1984-03-30
Volume volume18
Issue issue1
Start Page 91
End Page 100
ISSN 0475-0071
language 英語
File Version publisher
NAID 120002307204
JaLCDOI 10.18926/15790
FullText URL Mem_Sch_Eng_OU_16_1_21.pdf
Author Koga, Ryuji| Kosaka, Megumi| Sano, Hiroya|
Abstract In a sensitive spectrometry with lead-salt diode lasers, etalon-fringe phenomena often intervene in the measured absorption spectrum. Derivative methods are employed for the purpose of high resolution where the pertaining wavelength is modulated. This paper presents results of mathematical examination on a possible improvement of immunity from the etalon-fringes by choosing the profile of the wavelength modulation.
Publication Title Memoirs of the School of Engineering, Okayama University
Published Date 1982-03-01
Volume volume16
Issue issue1
Start Page 21
End Page 30
ISSN 0475-0071
language 英語
File Version publisher
NAID 120002307691
JaLCDOI 10.18926/15794
FullText URL Mem_Sch_Eng_OU_19_2_13.pdf
Author Koga, Ryuji| Kosaka, Megumi| Sano, Hiroya|
Abstract A quasi-random method for spectral scanning is proposed to reduce an alias response to a quick change in the source abundance. A direct application is made for an atmospheric methane monitoring with a current-tunable diode laser. Only barrel shift methods are examined being found further vulnerable to drifting etalon fringes.
Publication Title Memoirs of the School of Engineering, Okayama University
Published Date 1985-02-25
Volume volume19
Issue issue2
Start Page 13
End Page 22
ISSN 0475-0071
language 英語
File Version publisher
NAID 120002308000