Pub Date : 2002-11-07DOI: 10.1109/THZ.2002.1037609
S. Nishizawa, H. Kitahara, N. Tsumura, M. Takeda, S. Kojima
A new compact instrument of terahertz time-domain spectrometry (THz-TDS) has been developed to expand the THz-TDS adaptation for far-infrared quantitative measurements on functional materials. THz-TDS enables us to measure simultaneously the spectral amplitude and phase shift in the far-infrared region between 1 and 100 cm/sup -1/ so that the real and imaginary parts of complex dielectric function can be estimated independently without the Kramers-Kronig analysis. The details of the new compact instrument of THz-TDS are introduced, and the complex dielectric function and the phonon-polariton dispersion relation of ferroelectric Li/sub 2/Ge/sub 7/O/sub 15/ at 295 K are estimated and they are elucidated in terms of the Kurosawa formula.
{"title":"Terahertz time-domain spectroscopic study of ferroelectrics","authors":"S. Nishizawa, H. Kitahara, N. Tsumura, M. Takeda, S. Kojima","doi":"10.1109/THZ.2002.1037609","DOIUrl":"https://doi.org/10.1109/THZ.2002.1037609","url":null,"abstract":"A new compact instrument of terahertz time-domain spectrometry (THz-TDS) has been developed to expand the THz-TDS adaptation for far-infrared quantitative measurements on functional materials. THz-TDS enables us to measure simultaneously the spectral amplitude and phase shift in the far-infrared region between 1 and 100 cm/sup -1/ so that the real and imaginary parts of complex dielectric function can be estimated independently without the Kramers-Kronig analysis. The details of the new compact instrument of THz-TDS are introduced, and the complex dielectric function and the phonon-polariton dispersion relation of ferroelectric Li/sub 2/Ge/sub 7/O/sub 15/ at 295 K are estimated and they are elucidated in terms of the Kurosawa formula.","PeriodicalId":143116,"journal":{"name":"Proceedings, IEEE Tenth International Conference on Terahertz Electronics","volume":"5 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-11-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114267793","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}
Pub Date : 2002-11-07DOI: 10.1109/THZ.2002.1037574
H. Willenberg, G. Scalari, G. Dohler, J. Faist
We present a microscopic model, based on a density matrix formalism, which unifies the apparently quite different gain mechanisms in intersubband transitions: the inversion gain of a quantum cascade laser and the Bloch gain in a periodic superlattice. The theory also provides an expression for the spontaneous emission in intersubband transitions, which accounts for the temperature-dependent asymmetry of measured luminescence spectra. While the luminescence profile is hardly altered, the peak gain position depends critically on the ratio of populations. Thus, the degree of population inversion is accessible by simultaneous observation of both signals. For these measurements, whispering gallery quantum cascade laser are particularly suitable as scattered laser light and luminescence are of comparable strength over a wide range of injected currents.
{"title":"Bloch gain in a quantum cascade laser","authors":"H. Willenberg, G. Scalari, G. Dohler, J. Faist","doi":"10.1109/THZ.2002.1037574","DOIUrl":"https://doi.org/10.1109/THZ.2002.1037574","url":null,"abstract":"We present a microscopic model, based on a density matrix formalism, which unifies the apparently quite different gain mechanisms in intersubband transitions: the inversion gain of a quantum cascade laser and the Bloch gain in a periodic superlattice. The theory also provides an expression for the spontaneous emission in intersubband transitions, which accounts for the temperature-dependent asymmetry of measured luminescence spectra. While the luminescence profile is hardly altered, the peak gain position depends critically on the ratio of populations. Thus, the degree of population inversion is accessible by simultaneous observation of both signals. For these measurements, whispering gallery quantum cascade laser are particularly suitable as scattered laser light and luminescence are of comparable strength over a wide range of injected currents.","PeriodicalId":143116,"journal":{"name":"Proceedings, IEEE Tenth International Conference on Terahertz Electronics","volume":"27 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-11-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129416839","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}
Pub Date : 2002-11-07DOI: 10.1109/THZ.2002.1037595
J. M. Chamberlain, N. N. Zinovev, A. Fitzgerald, E. Berry, G. Walker, J. Handley, M.A. Smith, R. Miles
This contribution attempts to answer the questions of how THz images are best processed, analyzed, presented, classified and interpreted, especially within a clinical setting. The solutions to these problems are reviewed within the context of recent imaging work on tumours and dental tissue, largely conducted by the Teravision group. It is concluded that compound images, especially those involving pulse broadening as an image parameter, are highly promising routes to visualisation. The possibility of using computer vision and data compression techniques is also discussed.
{"title":"What constitutes a useful and meaningful terahertz image?","authors":"J. M. Chamberlain, N. N. Zinovev, A. Fitzgerald, E. Berry, G. Walker, J. Handley, M.A. Smith, R. Miles","doi":"10.1109/THZ.2002.1037595","DOIUrl":"https://doi.org/10.1109/THZ.2002.1037595","url":null,"abstract":"This contribution attempts to answer the questions of how THz images are best processed, analyzed, presented, classified and interpreted, especially within a clinical setting. The solutions to these problems are reviewed within the context of recent imaging work on tumours and dental tissue, largely conducted by the Teravision group. It is concluded that compound images, especially those involving pulse broadening as an image parameter, are highly promising routes to visualisation. The possibility of using computer vision and data compression techniques is also discussed.","PeriodicalId":143116,"journal":{"name":"Proceedings, IEEE Tenth International Conference on Terahertz Electronics","volume":"28 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-11-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114794719","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}
Pub Date : 2002-11-07DOI: 10.1109/THZ.2002.1037573
R. Kohler, A. Tredicucci, F. Beltram, H. Beere, E. H. Linfield, A. Davies, D. A. Ritchie, R.C. Iotti, F. Rossi
The terahertz region (1-10 THz) of the electromagnetic spectrum offers ample opportunities in spectroscopy, free space communications, remote sensing and medical imaging. Yet, the use of THz waves in all these fields has been limited by the absence of appropriate sources. Existing solid-state emitters, in fact, lack the general requisites of compactness, integrability and portability necessary for implementation in actual devices, and suffer from low output powers, limited tunability, and/or the necessity of liquid helium cryogenics. Research on THz semiconductor lasers has received new life in the last few years thanks to the development of quantum cascade (QC) lasers of ever increasing wavelength. Yet, fundamental problems related to the transition energy being below the optical phonon resonance and to efficient confinement of the emitted radiation have seriously hampered the realization of THz QC devices. With the help of detailed theoretical modelling and the adoption of a special partially metallic waveguide, we have now demonstrated a monolithic THz heterostructure laser based on interminiband transitions in the conduction band of a GaAs/AlGaAs QC heterostructure. Single mode emission has been achieved at 4.4 THz (/spl lambda/ /spl sim/ 67 /spl mu/m) with high output powers of more than 2 mW. Although operation is presently limited to 60 K, the low threshold current density of less than 300 A/cm/sup 2/ testifies the great development potential for higher temperatures.
{"title":"Terahertz quantum cascade lasers","authors":"R. Kohler, A. Tredicucci, F. Beltram, H. Beere, E. H. Linfield, A. Davies, D. A. Ritchie, R.C. Iotti, F. Rossi","doi":"10.1109/THZ.2002.1037573","DOIUrl":"https://doi.org/10.1109/THZ.2002.1037573","url":null,"abstract":"The terahertz region (1-10 THz) of the electromagnetic spectrum offers ample opportunities in spectroscopy, free space communications, remote sensing and medical imaging. Yet, the use of THz waves in all these fields has been limited by the absence of appropriate sources. Existing solid-state emitters, in fact, lack the general requisites of compactness, integrability and portability necessary for implementation in actual devices, and suffer from low output powers, limited tunability, and/or the necessity of liquid helium cryogenics. Research on THz semiconductor lasers has received new life in the last few years thanks to the development of quantum cascade (QC) lasers of ever increasing wavelength. Yet, fundamental problems related to the transition energy being below the optical phonon resonance and to efficient confinement of the emitted radiation have seriously hampered the realization of THz QC devices. With the help of detailed theoretical modelling and the adoption of a special partially metallic waveguide, we have now demonstrated a monolithic THz heterostructure laser based on interminiband transitions in the conduction band of a GaAs/AlGaAs QC heterostructure. Single mode emission has been achieved at 4.4 THz (/spl lambda/ /spl sim/ 67 /spl mu/m) with high output powers of more than 2 mW. Although operation is presently limited to 60 K, the low threshold current density of less than 300 A/cm/sup 2/ testifies the great development potential for higher temperatures.","PeriodicalId":143116,"journal":{"name":"Proceedings, IEEE Tenth International Conference on Terahertz Electronics","volume":"24 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-11-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130062934","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}
Pub Date : 2002-11-07DOI: 10.1109/THZ.2002.1037616
H. Minamide, K. Kawase, K. Imai, H. Ito
We demonstrate THz-wave imaging using a widely tunable THz-wave parametric oscillator. Two Si-bolometer detectors were used to obtain stable measurements. The imaging system was controlled by a PC using the program Labview. The targets of the THz-wave imaging were a T-shaped piece of polyethylene and a P-shaped piece of Teflon within an envelope that was opaque for visible light. We obtained clear images at 1.6 and 1.8 THz. Moreover, a unique differential image was successfully derived from the difference between the 1.6 and 1.8 THz images.
{"title":"Differential imaging using a THz-wave parametric oscillator","authors":"H. Minamide, K. Kawase, K. Imai, H. Ito","doi":"10.1109/THZ.2002.1037616","DOIUrl":"https://doi.org/10.1109/THZ.2002.1037616","url":null,"abstract":"We demonstrate THz-wave imaging using a widely tunable THz-wave parametric oscillator. Two Si-bolometer detectors were used to obtain stable measurements. The imaging system was controlled by a PC using the program Labview. The targets of the THz-wave imaging were a T-shaped piece of polyethylene and a P-shaped piece of Teflon within an envelope that was opaque for visible light. We obtained clear images at 1.6 and 1.8 THz. Moreover, a unique differential image was successfully derived from the difference between the 1.6 and 1.8 THz images.","PeriodicalId":143116,"journal":{"name":"Proceedings, IEEE Tenth International Conference on Terahertz Electronics","volume":"34 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-11-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131645773","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}
Pub Date : 2002-11-07DOI: 10.1109/THZ.2002.1037613
A. Abo-Bakr, J. Feikes, K. Holldack, U. Schade, G. Wustefeld, H. Hubers
A new technology for generating high quality and powerful terahertz (THz) radiation is presented. Coherent THz synchrotron radiation is produced in a 'low alpha' optics mode of the synchrotron light source BESSY II. The radiated power grows with the square of the beam current. Compared to the normal, incoherent emission process the power grows up to 100,000 times in the range of 03-1.2 THz (10 cm/sup -1/-40 cm/sup -1/).
{"title":"Coherent THz synchrotron radiation at BESSY II","authors":"A. Abo-Bakr, J. Feikes, K. Holldack, U. Schade, G. Wustefeld, H. Hubers","doi":"10.1109/THZ.2002.1037613","DOIUrl":"https://doi.org/10.1109/THZ.2002.1037613","url":null,"abstract":"A new technology for generating high quality and powerful terahertz (THz) radiation is presented. Coherent THz synchrotron radiation is produced in a 'low alpha' optics mode of the synchrotron light source BESSY II. The radiated power grows with the square of the beam current. Compared to the normal, incoherent emission process the power grows up to 100,000 times in the range of 03-1.2 THz (10 cm/sup -1/-40 cm/sup -1/).","PeriodicalId":143116,"journal":{"name":"Proceedings, IEEE Tenth International Conference on Terahertz Electronics","volume":"14 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-11-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133240689","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}
Pub Date : 2002-11-07DOI: 10.1109/THZ.2002.1037577
W. Knap, Y. Deng, V. Kachorovskii, S. Rumyantsev, M. Shur
We review our recent experimental and theoretical studies of the detection of terahertz radiation in GaAs/AlGaAs heterostructure field effect transistors (FET's) in a wide range of temperatures (8-300 K) and for frequencies ranging from 0.1 THz to 0.6 THz. The resonant detection of 0.6 THz radiation by the two-dimensional electron plasma confined in 0.15 /spl mu/m gate length GaAs/AlGaAs field effect transistors is demonstrated.
{"title":"Detection of terahertz radiation by plasma waves in field effect transistors","authors":"W. Knap, Y. Deng, V. Kachorovskii, S. Rumyantsev, M. Shur","doi":"10.1109/THZ.2002.1037577","DOIUrl":"https://doi.org/10.1109/THZ.2002.1037577","url":null,"abstract":"We review our recent experimental and theoretical studies of the detection of terahertz radiation in GaAs/AlGaAs heterostructure field effect transistors (FET's) in a wide range of temperatures (8-300 K) and for frequencies ranging from 0.1 THz to 0.6 THz. The resonant detection of 0.6 THz radiation by the two-dimensional electron plasma confined in 0.15 /spl mu/m gate length GaAs/AlGaAs field effect transistors is demonstrated.","PeriodicalId":143116,"journal":{"name":"Proceedings, IEEE Tenth International Conference on Terahertz Electronics","volume":"32 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-11-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116037363","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}
Pub Date : 2002-11-07DOI: 10.1109/THZ.2002.1037603
V. Krozer, G. Loata, J. Grajal de la Fuente, P. Sanz
We discuss the limitations in power generation with Schottky diode and HBV (heterostructure barrier varactor) diode frequency multipliers. It is shown that at lower frequencies the experimental results achieved so far approach the theoretical limit of operation for the employed devices. However, at increasing frequencies the power drops with f/sup -3/ instead of the f/sup -2/ predicted by theory. In this contribution we provide an overview of state-of-the-art results. A comparison with theoretically achievable multiplier performance reveals that the devices employed at higher frequencies are operating inefficiently and the design and fabrication capabilities have not reached the maturity encountered at lower THz frequencies.
{"title":"Limitations in THz power generation with Schottky diode varactor frequency multipliers","authors":"V. Krozer, G. Loata, J. Grajal de la Fuente, P. Sanz","doi":"10.1109/THZ.2002.1037603","DOIUrl":"https://doi.org/10.1109/THZ.2002.1037603","url":null,"abstract":"We discuss the limitations in power generation with Schottky diode and HBV (heterostructure barrier varactor) diode frequency multipliers. It is shown that at lower frequencies the experimental results achieved so far approach the theoretical limit of operation for the employed devices. However, at increasing frequencies the power drops with f/sup -3/ instead of the f/sup -2/ predicted by theory. In this contribution we provide an overview of state-of-the-art results. A comparison with theoretically achievable multiplier performance reveals that the devices employed at higher frequencies are operating inefficiently and the design and fabrication capabilities have not reached the maturity encountered at lower THz frequencies.","PeriodicalId":143116,"journal":{"name":"Proceedings, IEEE Tenth International Conference on Terahertz Electronics","volume":"5 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-11-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132680745","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}
Pub Date : 2002-11-07DOI: 10.1109/THZ.2002.1037601
S. Dhillon, A. Davies, D. D. Arnone, H. Beere, D. Ritchie, E. Linfield
We report a study of a far-infrared GaAs-Al/sub 0.15/Ga/sub 0.85/As quantum cascade electro-luminescence device designed to emit via both diagonal and vertical transitions. Each type of transition was preferentially chosen by varying the applied electric field. The different transitions were identified by correlation with bandstructure calculations, electrical characteristics and the width of the peaks. Further, the importance of contact resistance on the spectra was shown.
{"title":"Diagonal and vertical far-infrared transitions from quantum cascade emitters","authors":"S. Dhillon, A. Davies, D. D. Arnone, H. Beere, D. Ritchie, E. Linfield","doi":"10.1109/THZ.2002.1037601","DOIUrl":"https://doi.org/10.1109/THZ.2002.1037601","url":null,"abstract":"We report a study of a far-infrared GaAs-Al/sub 0.15/Ga/sub 0.85/As quantum cascade electro-luminescence device designed to emit via both diagonal and vertical transitions. Each type of transition was preferentially chosen by varying the applied electric field. The different transitions were identified by correlation with bandstructure calculations, electrical characteristics and the width of the peaks. Further, the importance of contact resistance on the spectra was shown.","PeriodicalId":143116,"journal":{"name":"Proceedings, IEEE Tenth International Conference on Terahertz Electronics","volume":"43 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-11-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133145695","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}
Pub Date : 2002-11-07DOI: 10.1109/THZ.2002.1037593
B. Fischer, M. Walther, P. Jepsen
The far-infrared dielectric properties of organic acids and bases in the condensed phase are dominated by hydrogen bonding between the individual molecules. We have investigated the dielectric properties of nucleobases, nucleosides, and nucleotides. We find that at cold temperatures distinct vibrational modes are present in the frequency range 0.1-4 THz. These modes originate from ordered hydrogen bonds between the molecules.
{"title":"Far-infrared spectroscopy of hydrogen bonding in nucleobases, nucleosides, and nucleotides","authors":"B. Fischer, M. Walther, P. Jepsen","doi":"10.1109/THZ.2002.1037593","DOIUrl":"https://doi.org/10.1109/THZ.2002.1037593","url":null,"abstract":"The far-infrared dielectric properties of organic acids and bases in the condensed phase are dominated by hydrogen bonding between the individual molecules. We have investigated the dielectric properties of nucleobases, nucleosides, and nucleotides. We find that at cold temperatures distinct vibrational modes are present in the frequency range 0.1-4 THz. These modes originate from ordered hydrogen bonds between the molecules.","PeriodicalId":143116,"journal":{"name":"Proceedings, IEEE Tenth International Conference on Terahertz Electronics","volume":"76 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-11-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123282323","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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