EP2115407A2 - Système de mesure de spectre - Google Patents

Système de mesure de spectre

Info

Publication number
EP2115407A2
EP2115407A2 EP08708289A EP08708289A EP2115407A2 EP 2115407 A2 EP2115407 A2 EP 2115407A2 EP 08708289 A EP08708289 A EP 08708289A EP 08708289 A EP08708289 A EP 08708289A EP 2115407 A2 EP2115407 A2 EP 2115407A2
Authority
EP
European Patent Office
Prior art keywords
radiation
measuring system
terahertz
optical element
radiation source
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP08708289A
Other languages
German (de)
English (en)
Inventor
Urs Boegli
Philipp Bachmann
Dieter Lubkoll
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
MSA Auer GmbH
Original Assignee
MSA Auer GmbH
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from DE200710006082 external-priority patent/DE102007006082B4/de
Application filed by MSA Auer GmbH filed Critical MSA Auer GmbH
Publication of EP2115407A2 publication Critical patent/EP2115407A2/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
    • G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
    • G01N21/3581—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light using far infrared light; using Terahertz radiation
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
    • G01J3/02—Details
    • G01J3/10—Arrangements of light sources specially adapted for spectrometry or colorimetry
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
    • G01J3/28—Investigating the spectrum
    • G01J3/42—Absorption spectrometry; Double beam spectrometry; Flicker spectrometry; Reflection spectrometry
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
    • G01J3/28—Investigating the spectrum
    • G01J3/42—Absorption spectrometry; Double beam spectrometry; Flicker spectrometry; Reflection spectrometry
    • G01J3/433—Modulation spectrometry; Derivative spectrometry
    • G01J3/4338—Frequency modulated spectrometry
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
    • G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
    • G01N21/3563—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light for analysing solids; Preparation of samples therefor

Definitions

  • the invention relates to the generation and detection of coherent waves with frequencies in the terahertz range.
  • terahertz wave radiation The generation and detection of terahertz wave radiation is of interest for many applications. Particularly in detection systems in security applications, terahertz wave radiation can be used to detect biological weapons material, explosives, illicit drugs, and many other hidden objects. So far, the application is limited by the high cost, the bulky systems and the difficult operation. The invention reveals some new ideas to realize a terahertz system at a moderate cost.
  • the known terahertz systems employ ultrashort laser pulses which are rectified in non-linear crystals or photo switches and thus shift their spectrum, which is usually in the near infrared range, to a band having a central frequency of 0 Hz , This is equivalent to a spectrum of nearly zero to several Thz.
  • Nonlinear optical difference frequency generation where the nonlinear element generates continuous (cw) THz waves at the beat frequency of two lasers.
  • the terahertz radiation corresponds to electromagnetic waves in the frequency range between the high-frequency electronics and the infrared radiation.
  • This band is also referred to as "far infrared” and is in the range of 0.1 to 10 THz (3 mm to 30 ⁇ m). Molecules have absorption bands in this area. Therefore, it is possible to this band for
  • Coherence characterizes how well a wave can interfere with itself at a different time.
  • the delay over which the phase or amplitude changes by a significant amount (and thus reduces the correlation by a significant amount) is defined as the coherence time TC.
  • the bandwidth of a wave with a long coherence time is very small and vice versa.
  • Coherent waves can interfere with themselves. Therefore, it is possible to form phase-dependent measuring systems for the optical range, comparable to lock-in amplifiers at the end of the low frequencies.
  • a laser can only oscillate in a few selected modes that are very coherent. By allowing many modes with a fixed phase relationship, it is possible to generate very short radiation pulses.
  • Nonlinear optics is the optic branch that describes the behavior of light in nonlinear media, ie, media in which the polarization P nonlinearly responds to the electric field E of light. This nonlinearity will typically observed only at very high light intensities, such as provided by pulsed lasers. Different frequency mixing operations are possible, for example:
  • THz-TDS Terahertz time-domain spectroscopy
  • the THz-TDS is compatible with the well-established Fourier
  • FTS Transformation spectroscopy
  • this is a homodyne system in the frequency domain, where the laser wavelengths are shifted from the IR to the THz band and back with the help of nonlinear elements.
  • nonlinear elements are Auston switches, semiconductors or inorganic crystals such as KNO or organic crystals such as DAST.
  • the reference laser pulse is delayed to scan or scan the received radiation in a strictly synchronous manner.
  • the resulting curve may be subjected to a Fourier transform, such as an FFT, to obtain a spectrum which is the product of the spectrum of the THz source with the transfer curve of the sample to be examined.
  • a process for producing terahertz waves is known, for example, from US Pat. No. 6,144,679.
  • two radiation sources are directed to a non-linear optical element, wherein the wavelengths of the radiation sources are selected such that in the non-linear element, a third radiation is generated whose frequency is in the terahertz range.
  • the invention is therefore based on the object to provide a spectral measuring system, which allows a rapid and reliable determination of substance properties.
  • the invention is further based on the object to provide a spectral measuring system, which is additionally easy to assemble.
  • Controlling radiation sources and read in coordination with this control a sensor for detecting a radiation based on the other radiation There are two possibilities for the realization: On the one hand, at least two radiation sources can be provided, of which at least one can be set with regard to the emitted wavelength. On the other hand, more than two radiation sources can be provided, which emit fixed, mutually different wavelengths.
  • the common inventive idea of the present solutions is based on the fact that a control unit has one or more radiation sources controls and reads in coordination with this control a sensor for detecting a radiation based on the other radiation.
  • the following possibilities are available for realization:
  • at least two radiation sources can be provided, of which at least one is adjustable with respect to the emitted wavelength.
  • more than two radiation sources can be provided, which emit fixed, mutually different wavelengths.
  • the idea is pursued to use a single radiation source, which is designed to be able to emit several wavelengths to generate terahertz waves, or to emit directly terahertz waves.
  • At least one radiation source which can be set with regard to the emitted wavelength can be provided, so that the associated terahertz frequencies sweep over a small band.
  • measuring system It is therefore a measuring device that is designed to both control an input variable for an object to be examined, as well as - in temporal coordination with this control - to capture a corresponding response or output from the object to be examined.
  • This measuring device thus goes far beyond a purely passive measuring device and also goes far beyond a generating device for predetermined radiation. Therefore, the subject invention is referred to as a "measuring system”.
  • radiation having a predetermined first wavelength here refers to an electromagnetic Radiation whose spectrum has a relative maximum at the predetermined wavelength.
  • substance property refers in summary to a composition as well as specific properties of an object to be examined.
  • a substance property may be that the object contains one or more substances.
  • the object to be examined could be a bag containing one or more different explosives.
  • specific properties the object to be examined could be, for example, the surface of an opened semiconductor chip whose operation is to be monitored. The Substanzeschaft in this case would then be a different reflectivity of the semiconductor tracks in response to different operating conditions.
  • Radiation according to a main aspect of the invention comprises at least two radiation sources, of which at least the first radiation source is adjustable in terms of its wavelength.
  • at least the first radiation source is adjustable in terms of its wavelength.
  • a plurality of radiation sources are provided, for example three or more, of which several or even all are adjustable in terms of their wavelength.
  • the first radiation source emits a first radiation having a predetermined set first wavelength and the second radiation source emits a second radiation having a predetermined second wavelength different from the first wavelength.
  • the radiation sources are preferably designed as lasers, for example Nd-YAG or diode lasers.
  • the first and second radiation together form a radiation combination which, in cooperation with various optical components, is brought into interaction with an object to be examined. In cooperation with other optical components, further radiation is produced, which is ultimately based on the first and second radiation.
  • Measuring system includes a sensor that responds to this further radiation. This additional radiation is converted by the sensor into an electrical signal. Furthermore, the measuring system according to the invention comprises a control unit. The control unit is designed to control the at least two radiation sources and to set the wavelength of the at least one adjustable radiation source and to read out the sensor.
  • a terahertz radiation is generated in a sample space region in which optionally the object to be examined is located, depending on the radiation of the at least two radiation sources.
  • the wavelength of terahertz radiation depends on the wavelengths of the
  • Radiation sources from. By varying the wavelength of the adjustable radiation source and with the
  • Wavelength variation coordinated readout of the sensor the measuring system according to the invention is possible to record a terahertz spectrum of the object to be examined. Depending on the arrangement of the components to each other, this may be an absorption or a reflection spectrum. In this case, a slight detuning of the adjustable radiation source already causes a large variation in the generated terahertz range.
  • the great advantage of such a system is that many of the required elements are standard components in the field of fiber optics in telecommunications or in the near infrared region. In principle, the emitter or even the receiver could be realized in a single-chip solution or as a multi-chip module in a semiconductor package.
  • the spectral measurement system for determining substance properties using terahertz radiation has more than two radiation sources which emit radiations having mutually different specified wavelengths. Conceivable here are arrangements with three or four or more lasers with fixed wavelengths.
  • a control unit in this embodiment is designed to control this plurality of radiation sources in such a way that only exactly two of these plurality of radiation sources
  • Radiation sources on and the rest are turned off.
  • the control unit reads out the sensor, which responds to another radiation based on the combination of the two selected radiation sources.
  • N radiation sources N * (N-I) / 2 different radiation combinations can be realized.
  • a terahertz spectrum of an object to be examined can be recorded at N * (N-I) / 2 interpolation points.
  • the measuring system also has an input-output unit and a data memory, both with the control unit are connected. At least one terahertz spectrum of a known substance is stored in the data memory.
  • the control unit is designed to compare a terahertz spectrum of an object to be examined recorded as described above with the at least one stored terahertz spectrum and to output the result of the comparison to the input / output unit.
  • a known terahertz spectrum of an explosive could be stored in the data memory.
  • the control unit compares the currently measured spectrum with the stored spectrum. This comparison is made by a method known to be used to compare spectra. For example, a Euclidean distance between the measured and the stored spectrum could be calculated. If a predefinable threshold value is undershot, then a match is identified; if the threshold value is exceeded, a match is identified
  • the result of this determination is then output on the input / output unit.
  • the output may be such that in the event of a mismatch, only a text with the content "No match found" is output on a screen, while if a match occurs, an alarm signal will be output, along with the text "Alarm: Explosive A identified”. But it can also be sent via a network connection or a telecommunication connection (eg ISDN or GSM module) a warning message to predetermined persons or institutions.
  • a network connection or a telecommunication connection eg ISDN or GSM module
  • a warning message to predetermined persons or institutions.
  • a plurality of terahertz spectra of known substances can be deposited.
  • the control unit After recording the terahertz spectrum of an object to be examined, the control unit is then able to determine by comparison of the stored spectra with the recorded spectrum, which substance is in the object to be examined.
  • terahertz spectra of conventional explosives and terahertz spectra of conventional (harmless) packaging or pocket material such as leather, PE, linen, etc. could be deposited.
  • greater safety can be achieved so that a necessary alarm is not suppressed.
  • the measuring system according to the invention is able to determine also substance compositions. Pre-recorded measurement series with combinations of more than two components are also possible. In this way the reliability of the measuring system is increased. For security applications, this can be crucial. Particularly advantageous in this measurement system is that even untrained operating personnel can work with it. Thus, this system can be easily used, for example, in airports, where usually a high throughput of examinations is required.
  • the beam paths of the radiation sources are directed in the measuring system according to the invention to a reference beam splitter such that a partial beam on a first optical element falls and a second partial beam is directed to a deflection system.
  • a radiation field can then be emitted which, in addition to the irradiated wavelengths, can comprise further wavelengths.
  • a second optical element is arranged in relation to the first optical element and the deflection system such that it comprises at least part of the radiation of the
  • Radiation field can record.
  • the first optical element, the second optical element and the sample space area containing the sample may be arranged in a row one behind the other. Then the sample would be virtually illuminated, so it would be measured in transmission. This is useful when examining liquid or gaseous media.
  • the optical elements could also be arranged in relation to the sample such that it is measured in reflection. This is advantageous if, for example, the activity of a semiconductor chip is to be observed.
  • a radiation is emitted by the second optical element, which radiation can be detected by the sensor.
  • the radiation sources are designed as lasers and the first and second optical elements as non-linear optical elements.
  • the radiation sources are designed as diode lasers.
  • Diode lasers have the particular advantage of being small and relatively inexpensive.
  • the radiation combination of the radiation sources and the first nonlinear optical element cooperate in such a way that the radiation field is a radiation in the terahertz range from 0.1 terahertz to 100 terahertz. This frequency range is particularly well suited for irradiating opaque samples. While X-rays are too dangerous and conventional infrared radiation and visible light are too weak, the
  • Terahertz radiation is a convenient way to safely and safely sample samples.
  • the deflection system can be realized by mirrors, but alternatively it is also intended to use light-conducting fibers.
  • About the deflection system is the undisturbed, i. directed by the non-linear optical element, radiation combination of the radiation sources as reference radiation to the second non-linear optical element.
  • the terahertz radiation and the reference radiation then interact with one another in such a way that again easily detectable radiation is produced.
  • the radiation sources are integrated with a radiation amplifier on a semiconductor chip. This allows a particularly compact design. In addition, the manufacture and the adjustment during assembly of the measuring system according to the invention are considerably simplified.
  • the measuring system allows at least one of the radiation sources modulated sinusoidally or rectangularly becomes. In this way, the deviation of the absorption spectra can be measured.
  • the beam paths of the more than two radiation sources can be arranged such that they are directed onto the first optical element, so that a plurality of terahertz waves can be generated according to predetermined switching frequencies of the radiation sources.
  • each radiation source can be connected to a different frequency, so that the resulting terahertz waves can be modulated at different frequencies.
  • the phase matching in the first optical element is improved by different phase angles of the incident radiation. It is a well known problem in nonlinear optics that the new radiation fields generated by the nonlinear effects travel at different velocities in the nonlinear element than the originally irradiated radiation fields. This can cause phase relationships that lead to unwanted destructive interference. This problem is solved by the so-called phase-matching (index-matching, refractive indices). By appropriate use of dispersion and birefringence, as well as suitable arrangement of the radiation fields with respect to the axes of the anisotropic non-linear optical element can be set a more favorable interference behavior.
  • the radiations are the
  • Radiation sources coupled to optical fibers.
  • deflecting mirrors which need to be complicatedly adjusted first, so that the radiations fall in a predetermined manner on the first optical element.
  • the radiations of the radiation sources can be coupled to a single optical fiber. If only one fiber is present, it is particularly easy to direct the emerging radiation field onto the first optical element. This simplifies once again the manufacture of the measuring system.
  • the exit end of said fiber is arrangeable with respect to the first optical element and the second optical element such that the radiation exiting the fiber may partially fall on the first optical element and partially on the second optical element. This is achieved in that at the outlet end of the fiber, a beam splitter is arranged, whose one radiation exit surface of the first optical element and the other
  • imaging optical elements are provided.
  • optical elements may be, for example, made of polyethylene lenses. These lenses can also be designed as Fresnel lenses. At least one of the optical elements is implemented as a nonlinear optical element consisting of DAST (dimethylamino-4-N-methylstilbazolium tosylate), KDP, ADP, lithium niobate, Ba2NaNb5O15, quartz, GaAs, GaP, BaTiO3, ZnO or CdS.
  • DAST dimethylamino-4-N-methylstilbazolium tosylate
  • KDP dimethylamino-4-N-methylstilbazolium tosylate
  • ADP lithium niobate
  • Ba2NaNb5O15 quartz
  • quartz GaAs
  • GaP GaP
  • BaTiO3, ZnO or CdS This list of possible starting materials is to be considered as exemplary only. Other suitable materials may also be suitable for use.
  • control unit can be designed as an ASIC. If the control unit is designed as an ASIC, a lightweight and inexpensive mass production is possible. Alternatively, the control unit can also be designed as a DSP. This makes a particularly fast processing of the measured data possible. In this way, currently measured spectra with a large number of nodes can be quickly compared with the stored spectra, so that a rapid and very reliable indication of substance properties is possible.
  • control unit can alternatively be designed as an embedded system. This is particularly advantageous for measurement setups in the field of research. This facilitates easier reconfigurability and adaptation to changing measurement tasks.
  • the data memory can be configured by an external source. In this way, dynamically, i. even after a production and
  • the measuring system it is possible with the measuring system according to the invention to configure the data memory via a network connection, an internet connection, a telecommunication connection or an inductive connection.
  • Reconfiguring the memory may include adding more records.
  • the measuring system thus makes it possible to identify substances or substance properties, the specific features of a terahertz radiation being used.
  • the suitable control of a plurality of radiation sources results in a temporal sequence of predetermined terahertz wavelengths being produced in a first nonlinear optical element. In this way, virtually a spectrum is driven through.
  • the measurement of the resulting radiation with the aid of a further nonlinear optical element leads to spectral information of the substance or structure to be investigated.
  • the control unit compares this spectral information with spectra of already known substances or structures, which spectra are stored in the data memory.
  • control unit can determine which substance / substances / structures are present in the test object to be examined. This allows a particularly rapid identification of hazardous substances. Since the measuring system according to the invention can be operated very easily, it is highly suitable, for example, for securing in airports or for counter-terrorism.
  • the measurement system according to the invention comprises nonlinear elements, such as DAST crystals, which are operated by one or more lasers.
  • nonlinear elements such as DAST crystals
  • more than two lasers can be provided.
  • a predetermined spectral range can be detected quasi-simultaneously.
  • the detection itself can be done optically synchronously using a second non-linear element by homodyne detection.
  • N lasers so that a plurality of frequencies in the terahertz range can be generated.
  • N lasers it is possible to generate N * (NI) / 2 different terahertz wavelengths.
  • each terahertz wave can be modulated below individual frequencies if each laser is modulated with pulses at different repetition rates.
  • the pulse repetition rate of the lasers must be selected in this way be that the beat frequencies between the pulse repetition rates of all lasers are different.
  • This scheme can be used to capture each of the terahertz waves with phase-sensitive elements, such as lock-in amplifiers, at their individual frequency.
  • radiations of at least two predetermined mutually different wavelengths are emitted by the radiation source.
  • Predetermined means that it is determined by the dimensions or the control, which wavelengths are emitted. It can also be provided that at least one of the wavelengths is adjustable.
  • the laser resonator is operated so that the laser has two radiations different from each other
  • the advantage of such a laser is that it can already be manufactured as a module during manufacture, so that no further fine adjustment is required when installed in a measuring system.
  • the emitted wavelengths differ only slightly.
  • the beats resulting from the superposition of the decoupled wavelengths are directed to an optical element that converts this radiant energy into terahertz waves.
  • the two-color diode laser may be configured such that at least one of its wavelengths is adjustable during operation.
  • the two-color diode laser is based on the fact that two adjoining areas of a semiconductor have a different geometry, so that in one and the same semiconductor two different laser regions with correspondingly different wavelengths are present.
  • the resonator mirror is moved for only the one laser region.
  • the sensor responds to radiation which is based on the radiation of the radiation source.
  • the superposition of the at least two radiations results in producing a third radiation having a wavelength different from the wavelengths of the first at least two radiations.
  • This third radiation is advantageously a terahertz radiation.
  • the radiation source itself emits terahertz radiation.
  • This terahertz radiation is emitted by a first element.
  • This element may be embodied as an optical element, for example as a nonlinear optical element, or as an electrical element, for example as a photoconductive antenna.
  • an intense light pulse of short duration, about 1 ps is directed to a photoconductive antenna to which a voltage is applied. The light pulse generates free
  • the second element may be an optical or electrical element as described.
  • the radiation source in the measuring system generates a comb of terahertz radiation.
  • the generation of such a terahertz frequency comb is described, for example, in "Terahertz Comb Frequency Generation in Nonlinear Optical Devices", Proc. of SPIE, Vol. 6373 (2006).
  • Such a selection of a radiation source has the advantage that a plurality of frequencies are present simultaneously and the control of the radiation source is simplified.
  • the measuring system thus enables identification of substances or
  • Figure 1 is a schematic representation of the spectral measuring system in a first embodiment
  • Figure 2 shows three terahertz spectra of different explosives
  • Figure 3 is a schematic representation of the spectral measuring system in a second embodiment
  • FIG. 4 a shows a schematic drive diagram of the lasers in the spectral measuring system in the second embodiment
  • FIG. 4b shows an alternative schematic driving diagram of the lasers in the measuring system in the second
  • Figure 5 is a schematic representation of the spectral measuring system in a third embodiment
  • Figure 6 is a schematic representation of the spectral measuring system in a fourth embodiment
  • Figure 7 is a schematic representation of the spectral measuring system in a fifth embodiment
  • Figure 8 is a schematic representation of the spectral
  • Figure 9 is a schematic representation of the spectral
  • FIG. 10 is a schematic representation of a terahertz
  • FIG. 1 shows the first embodiment of the spectral measuring system according to the invention.
  • a first laser 10 first radiation source
  • a second laser 20 second
  • the control unit 40 is configured to turn the lasers 10 and 20 on and off.
  • the control unit 40 is further capable of adjusting the wavelength of at least one of the lasers 10, 20. This is achieved by a suitable adjustment of the temperature and the operating current of the respective laser 10, 20.
  • the wavelength of the laser 10 is set in a predetermined manner.
  • the laser 10 emits with an adjustable wavelength that is in a wavelength range of 1580 to 1600 nm while the laser 20 is fixedly set to a wavelength of 1602 nm. In this way an adjustable terahertz radiation of 0.23 to 2.6 phr can be generated by means of a non-linear optical element.
  • the exit opening of the first laser 10 is directed to an opaque mirror 11, which is arranged so that it blocks the radiation of the first laser 10 on a
  • Entrance surface of a downstream beam splitter 21 directed.
  • the outlet opening of the second laser 20 is directed onto a second entrance surface of the beam splitter 21.
  • multiple lasers may be used be provided (see below).
  • the exit surface of the first beam splitter 21 faces the entrance surface of the second beam splitter 51.
  • An exit surface of the second beam splitter 51 is an entrance surface of a first nonlinear optical
  • Element 50 for example, a DAST crystal, facing.
  • a further exit surface of the second beam splitter 51 faces a beam deflecting device 52, 53.
  • the beam deflecting device 52, 53 is made up of two mirrors 52 and 53, but it may also be designed to be particularly easy to handle as an optical fiber 52 '.
  • the exit surface of the first nonlinear optical element 50 is arranged facing the entry surface of a second nonlinear optical element 60.
  • the second nonlinear optical element 60 may also be formed from a suitably prepared DAST crystal.
  • the space R between the two nonlinear optical elements 50 and 60 is intended to be as
  • Sample area R to record the object to be examined.
  • the nonlinear optical element 60 instead of guiding a portion of the transmitter radiation S5 "as a reference to the nonlinear optical element 60, radiation can be locally generated to shift the terahertz radiation back into the infrared. Analogously, this would be a local oscillator in the radio receiver. However, a bolometer or another terahertz detector can also be used directly without the nonlinear optical element 60. The different wavelengths in the terahertz range may then be indistinguishable, but they are because they are sensitively modulated at different frequencies.
  • the exit surface of the second nonlinear optical element 60 faces the radiation-sensitive surface of a suitable sensor 90. In the present embodiment, a commercially available photodiode having an appropriate spectral sensitivity is used.
  • a liquid helium-cooled bolometer may also be provided at this point.
  • the sensor 90 is intended to convert an incident radiation into an electrical signal, which then passes via an interface 49 to the control unit 40.
  • a suitable signal amplification can be provided.
  • the control unit 40 is connected to a data memory 70 and to an input / output unit 80.
  • the input-output unit 80 may be the usual combination of a computer screen with a corresponding keyboard.
  • the data memory 70 stores terahertz spectra of known substances. In other words, in the
  • Datastore 70 terahertz spectra of various substances deposited, these terahertz spectra were previously determined with a similar or comparable system by introducing known reference samples.
  • a control unit 40 is a commercial PC in question, which is provided with suitable interfaces and suitable software.
  • the spectral data in the data memory 70 are then present in one or more files that can be accessed by another software which is specific for spectral evaluations.
  • the lasers 10 and 20 emit laser radiation S1 and S2. This combination of radiations gives the beam S5.
  • the beam splitter 51 the beam S5 is split into the beams S5 'and S5' 1 .
  • the beam S5 ' is directed to the nonlinear element 50.
  • the non-linear superimposition of the laser radiation S 1 and S 2 results in a difference wavelength whose frequency lies in the terahertz range. This frequency is particularly well suited for safe and reliable fluoroscopy of various substances.
  • the resulting terahertz radiation field T is located directly downstream of the first nonlinear optical element.
  • the second nonlinear element 60 for example a photomixer, the resulting terahertz radiation T and the reference beam S5 ' 1 modified by the object to be examined are superimposed. This creates a further radiation S9.
  • This is again a radiation in the wavelength range of the near infrared, which in turn is detected by the sensor 90.
  • the readout measured value of the sensor 90 is stored together with the wavelength settings of the two lasers 10 and 20 in a temporary memory (not shown) of the control unit 40.
  • the tunable laser 10 is slightly detuned (ie adjusted) in a predetermined manner with respect to its emitted wavelength. This is done by a suitable temperature variation of the resonator in the laser.
  • the terahertz radiation now resulting in this way has a different frequency than the previously generated terahertz radiation.
  • the corresponding wavelength and the radiation detected by the sensor 90 are now stored in the control unit 40 in the temporary memory. This step can be so frequent to be repeated as necessary.
  • absorbance values are measured at at least three different terahertz frequencies.
  • the spectral measuring system has received at least three supporting points for the terahertz absorption spectrum of the substance to be examined. Since each substance has a characteristic terahertz spectrum, it is now possible for the control unit 40, on the basis of the spectra stored in the data memory 70 with associated substances, to output an indication of the substance currently being measured by comparison with the spectrum just measured.
  • Figure 2 shows three terahertz spectra of different explosives A, B and C. These are absorption spectra, the frequency is plotted to the right and the absorption in any
  • the explosive A has a relative absorption maximum at about 1.1 THz
  • the explosive B has a relative absorption maximum at about 0.8 THz
  • the explosive B has a weak relative absorption maximum at about 1.6 THz having.
  • the laser 10 is adjusted to cause, together with the laser 20 in a predetermined sequence, the emission of four different terahertz waves with frequencies t1, t2, t3 and t4 from the first nonlinear element.
  • the frequencies t1, t2, t3 and t4 are selected to include spectral characteristics of specific explosives are. As a spectral characteristic is advantageously a relative absorption maximum in question.
  • the control unit 40 is now able to find the stored spectrum by one or more comparison operations, which has a maximum similarity to the measured spectrum based on the four nodes, has.
  • the Euclidean distance between the measured spectrum and the stored spectra can be determined.
  • the spectrum deposited in which the Euclidean distance is minimal, most likely belongs to the substance that is currently also measured. If no substance was found in this process, a normalization of all the spectra to be compared can be carried out as an additional step. There are a number of known methods that can be used to determine the most likely composition of the substance to be examined, as well as a figure of merit, indicating the quality or statistical safety of the substance.
  • FIG. 3 shows a schematic representation of the spectral measuring system in a second embodiment according to the invention.
  • the same reference numerals as in Figure 1 denote the same components with the same
  • the difference from the first embodiment lies in the fact that here three lasers 10, 20 and 30 are provided, which emit at fixedly set different wavelengths.
  • the radiation of the laser 30 is coupled via the beam splitter 31, so that the beam S5 results.
  • Embodiment here is also the reference radiation S5 ' 1 deflected via an optical fiber 52' and directed to the second non-linear optical element 60.
  • the control of the lasers 10, 20 and 30 is effected by a comparison with the first embodiment modified control unit 40 '.
  • the second embodiment according to the invention has the advantage that none of the lasers (10, 20, 30) has to be detuned in order to achieve a spectral variation. Rather, the terahertz spectrum is scanned by emitting only two lasers each while the third laser is turned off. In this way, three different terahertz frequencies can be generated offset in time, by means of which at just these three nodes the
  • FIG. 4a shows a schematic control diagram of the lasers in the spectral measuring system in the second embodiment according to the invention.
  • Ll0, L20 and L30 designate the turn-on times of the respective lasers 10, 20 and 30.
  • the control unit 40 For example, at time Tl, only lasers 10 and 20 are turned on, so that the resulting terahertz radiation has a frequency of fl THz.
  • the control unit 40 or the data memory 70 is deposited, which combination of two lasers leads to which terahertz radiation.
  • Memory 70 'deposited spectra, which substance is most likely in space R.
  • the three lasers 10, 20, 30 are modulated with a different pulse frequency
  • the result for the terahertz radiations for each wavelength fi, ⁇ 2, fs is a different modulation frequency with the periods Period 1, Period 2.
  • the amplitudes can thus be measured at the receiver at three different modulation frequencies period 1, 2, 3, and thus the radiation at the regular terahertz wavelengths can be determined.
  • this is shown for two of the three possible terahertz frequencies.
  • the combination of the lasers 20, 30 is not visible in this representation, since their periods are greater than the period shown. This can also be measured quasi-continuously.
  • the evaluation using the table below should further explain the method, the following.
  • the table includes the absorbance values of explosive A ("cloth A”), explosive B ("cloth B”) and explosive C ("cloth C”) the terahertz frequencies 0.6, 0.8, 1 and 1.1 THz. Furthermore, the table contains a column ("measurement") with a measured terahertz spectrum from an object to be examined. In the respective column “Diff” next to the respective substance spectra ("Substance A", “Substance B” or “Substance C”), the square of the difference from the currently measured absorption value to the stored respective absorption value of a substance at the corresponding frequency is entered. The bottom line contains three values (6.24, 45.37 and 47.13). These are the square roots of the sum of the respective distance squares per substance spectrum. In other words, these are the Euclidean distances from the currently measured spectrum to the respective substance spectrum.
  • the deposited substance spectrum which has a minimal Euclidean distance to the measured spectrum of the object to be examined, shows with greatest
  • the training of Meßspektren can also be performed by neural networks.
  • FIG. 5 shows a schematic representation of the spectral measuring system in a third embodiment according to the invention.
  • three lasers 110, 120 and 130 are used, which are driven by a digital signal processor (DSP) 140 with data memory 170.
  • DSP digital signal processor
  • a material sample M can optionally be introduced into the resulting terahertz radiation field T.
  • the detector 190 converts the detected light intensity into an electrical signal received from the DSP is evaluated. The result of the evaluation is output by the DSP to the I / O unit 180.
  • FIG. 6 shows a schematic representation of the spectral measuring system in a fourth invention
  • Figure 7 shows a schematic representation of the spectral measuring system in a fifth embodiment of the invention, wherein similar reference numerals similar
  • An element SOA 350 emits terahertz radiation which is radiated into the sample space by an imaging element.
  • the imaging element 355 may be a lens, such as a Fresnel lens made of polyethylene.
  • the terahertz radiation penetrates the material M to be examined, is reflected by a reflecting surface R, and finally falls on a second imaging element 365, which may also be a Fresnel lens made of polyethylene.
  • the detector 390 detects the light passing through the second imaging element passing radiation and passes a corresponding signal to the DSP 340 on.
  • the structure of the spectral measuring system according to the invention shown in FIG. 7 - with the omission of a material M - is also suitable for detecting temporally variable surface qualities of the reflecting surface R. This makes substance properties measurable. This is particularly advantageous when investigating the activity of semiconductor chips.
  • the spectral measuring system enables a rapid and reliable determination of substances or substance properties without a user needing specialist knowledge and that the invention can be implemented using inexpensive freely available components. This is achieved by applying terahertz radiation to a material to be investigated for interaction with it under a plurality of predetermined wavelengths and evaluating the resulting radiation from a control unit having an associated data memory containing spectral measurement data.
  • FIG. 8 shows the sixth embodiment of the spectral measuring system according to the invention.
  • the exit aperture of the radiation source 410 is directed to an opaque mirror 411 which is arranged to direct the radiation of the radiation source 410 onto an entrance surface of a beam splitter 451 which splits the beam S405 into the beams S405 'and S405' '.
  • An exit surface of the beam splitter 451 faces an entrance surface of a first optical element 450, for example a DAST crystal or a photoconductive antenna.
  • a further exit surface of the beam splitter 451 faces a beam deflecting device 452, 453.
  • the beam deflecting device 452, 453 is made of two mirrors 452 and 453, but it may also be designed to be particularly easy to handle as an optical fiber.
  • the exit surface of the first optical element 450 is arranged facing the entry surface of a second optical element 460.
  • the second optical element 460 may also be formed of a suitably prepared DAST crystal or a photoconductive antenna - without applied external voltage.
  • the space R located between the two optical elements 450 and 460 is intended to accommodate, as the sample space region R, optionally the object to be examined.
  • the exit surface of the second optical element 460 faces the radiation-sensitive surface of a suitable sensor 490.
  • a suitable sensor 490 In the present embodiment, a commercial photodiode used with a suitable spectral sensitivity. In systems designed for purely research purposes, however, a liquid helium-cooled bolometer may also be provided at this point.
  • the sensor 490 is designed to convert an incident radiation into an electrical signal, which then passes via an interface 449 to the control unit 440. In this case, a suitable signal amplification can be provided.
  • the control unit 440 is connected to a data memory 470 as well as to an input / output unit 480.
  • the on-output unit 480 may be the usual combination of a computer screen with a corresponding keyboard.
  • the data memory 470 stores terahertz spectra of known substances. In other words, 470 terahertz spectra of various substances are stored in the data memory, these terahertz spectra having previously been determined using a similar or comparable system by introducing known reference samples.
  • FIG. 9 shows the seventh embodiment according to the invention of the spectral measuring system according to the invention. Similar reference symbols as in the figure previously shown here mean similar components.
  • Particularly advantageous in this embodiment is the direct generation of terahertz radiation by suitable electronic components such as large area GaAs or ZnTe emitter 550.
  • suitable electronic components such as large area GaAs or ZnTe emitter 550.
  • the radiation transmitted through the sample space or reflected by the sample radiation is picked up by a suitable sensor circuit 560, S509, 590 and a form of electrical measurement signals is sent to the control unit 540.
  • FIG. 10 shows an idealized schematic representation of a terahertz frequency comb.
  • a radiation power P is plotted against a terahertz frequency. It is clear that the terahertz
  • Radiation emitted by a suitable element has power maxima at various terahertz frequencies. In this way, a simultaneous spectrum of different terahertz frequencies is provided with a fixed distance between them. It is clear that, due to suitable dimensions of the radiation source and suitable control of the radiation source during operation, considerably more maxima can be provided than shown here. Also, the frequency comb as a whole can be adjusted in operation such that the frequencies of the maxima are varied or that the distances of the maxima are varied or both. If a radiation source with such a terahertz spectrum is used, control of the radiation source for further variation of the wavelengths can be dispensed with.
  • a spectral measurement system for determining substance properties using terahertz radiation, comprising: one or more radiation sources, at least one first radiation source being adjustable or configurable in wavelength, the first radiation source emits a first radiation having a predetermined first wavelength; and is characterized by a sensor responsive to further radiation based on the radiation of the at least one radiation source; a control unit associated with the at least one
  • Radiation source and the sensor is connected; wherein the control unit is designed to control the at least one radiation source and to adjust the wavelength of the at least one adjustable radiation source and to read out the sensor.
  • the spectral measuring system according to the invention can be made compact and allows a simple construction without complicated adjusting actions.

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Abstract

L'invention concerne un système de mesure de spectre pour déterminer les propriétés d'une substance au moyen d'un rayonnement térahertz, ce système comprenant : une ou plusieurs sources de rayonnement (10; 410), dont au moins une source (10) de rayonnement est réglable ou configurable en ce qui concerne sa longueur d'onde, la première source de rayonnement (10; 10 410) envoyant un premier rayonnement (S1; S401) avec une première longueur d'onde prédéterminée. L'invention est caractérisée par un capteur (90), qui réagit à un autre rayonnement (S9; S409), lequel se base sur le rayonnement (S1; S401) de la au moins une source de rayonnement (10; 410). Le système comporte aussi une unité de commande (40; 440), qui est reliée à la au moins une source de rayonnement (10; 410) et au capteur (90; 490), l'unité de commande (40; 440) étant conçue de façon à commander au moins une source de rayonnement (10; 410) et à régler la longueur d'onde d'au moins une source de rayonnement (10; 410) réglable ainsi qu'à lire le capteur (90; 490).
EP08708289A 2007-02-02 2008-01-28 Système de mesure de spectre Withdrawn EP2115407A2 (fr)

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DE200710006082 DE102007006082B4 (de) 2007-02-02 2007-02-02 Spektrales Messsystem
DE102007057850A DE102007057850A1 (de) 2007-02-02 2007-11-29 Spektrales Messsystem
PCT/EP2008/050971 WO2008092828A2 (fr) 2007-02-02 2008-01-28 Système de mesure de spectre

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2469945A (en) * 2008-04-04 2010-11-03 Emcore Corp Terahertz frequency domain spectrometer with integrated dual laser module

Families Citing this family (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102010019134B4 (de) * 2010-04-30 2019-08-08 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. THz-Messsystem und Sensoranordnungen sowie deren Verwendung
DE102010040356A1 (de) * 2010-09-07 2012-03-08 Universität Zu Köln THz-Spektrometer und THz-Spektroskopieverfahren
PT106056B (pt) 2011-12-12 2014-08-04 Inst Superior Técnico Dispositivo formado por uma linha magnética de transmissão, para uso em circuitos integrados, para aplicações na tecnologia terahertz
US20130298652A1 (en) * 2012-05-08 2013-11-14 Logimesh IP, LLC Systems and methods for asset monitoring
JP6220128B2 (ja) * 2013-01-08 2017-10-25 アークレイ株式会社 テラヘルツ波発生装置及びテラヘルツ波測定方法
US10739196B2 (en) * 2018-07-03 2020-08-11 Electronics And Telecommunications Research Institute Spectroscopic apparatus and spectroscopic method using orthogonal code
US11099072B2 (en) 2019-08-08 2021-08-24 Apple Inc. Terahertz spectroscopy and imaging in dynamic environments with spectral response enhancements
US11555792B2 (en) 2019-08-08 2023-01-17 Apple Inc. Terahertz spectroscopy and imaging in dynamic environments with performance enhancements using ambient sensors
US11513004B2 (en) 2019-08-08 2022-11-29 Apple Inc. Terahertz spectroscopy and imaging in dynamic environments
CN111257851B (zh) * 2020-04-03 2022-04-05 厦门大学 一种基于宽谱光源的光谱测量方法和光谱扫描激光雷达

Family Cites Families (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6144679A (en) * 1999-01-15 2000-11-07 Science Applications International Corporation Method and apparatus for providing a coherent terahertz source
GB2359716B (en) * 2000-02-28 2002-06-12 Toshiba Res Europ Ltd An imaging apparatus and method
US6859283B2 (en) * 2002-06-17 2005-02-22 Lightwave Electronics Corporation Apparatus and method for measuring phase response of optical detectors using multiple-beatnote optical heterodyne
GB2399626B (en) * 2003-03-21 2006-04-05 Teraview Ltd Spectroscopy apparatus and associated technique
US7919755B2 (en) * 2006-09-27 2011-04-05 Anis Rahman Dendrimer based electro-optic sensor
GB2418337B (en) * 2004-09-17 2008-07-16 Tera View Ltd An imaging apparatus and method
DE102007006082B4 (de) 2007-02-02 2010-04-15 Msa Auer Gmbh Spektrales Messsystem

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO2008092828A2 *

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2469945A (en) * 2008-04-04 2010-11-03 Emcore Corp Terahertz frequency domain spectrometer with integrated dual laser module
GB2469944A (en) * 2008-04-04 2010-11-03 Emcore Corp Integrated dual laser module for terahertz spectroscopy measurements of a target
GB2469945B (en) * 2008-04-04 2011-05-25 Emcore Corp Terahertz frequency domain spectrometer with integrated dual laser module
GB2469944B (en) * 2008-04-04 2011-05-25 Emcore Corp Terahertz frequency domain spectrometer with integrated dual laser module

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DE102007057850A1 (de) 2009-06-04
WO2008092828A2 (fr) 2008-08-07
WO2008092828A3 (fr) 2008-11-27

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