GB2505036A - Terahertz frequency domain spectrometer - Google Patents

Abstract

An apparatus 100 for analyzing, identifying or imaging a target includes first and second tunable lasers 105, 106 producing first and second different frequency beams, phase modulator 113 receiving a first portion of the first beam to controllably modulate the phase thereof and produce a modulated third beam, first optical element BC1 coupled to the third beam and a portion of the second beam to produce a composite output fourth beam, a source 201 of CW signals in a frequency range 100GHz- 2THz including a first photoconductive switch 204 activated by the fourth beam, a radiative element 205 coupled to the source 201 for causing the CW signals to be focussed on or through the target, a second optical element BC2 coupled to a portion of the first beam and the second beam to produce a composite fifth beam, a detector 202 for acquiring spectral information from said target and coupled to the fifth beam, and generating based on this information and the fifth beam a signal representing a characteristic of the target. The detection includes a heterodyne detection system 209.

Description

REflflNCE 10 flLATILD APPLICAnONS [0001] Ibis application s a. carttinuation-intpar. of 11.5. Patez.t.Applivathm Scxiai No. 12/861451, filed August 23, 2010 wInch ni tuin is a othmat'on-m-prt of U S Patent Application SerialNo. 12/465,219, filed May 13, 2009. now US. Patent No, 7,781.736, which application claims rioSy of US. Provisional. Application 8e4W No. 61/054344 flied May 19.

2008. Each of these applications is herein incorporated by reference in its entirety..

BACIWROUNI) 011 11W INVENTiON 1. k1d ef the Invenfion [0 002] The invention relates to miciowave, nidlimeter wave and subnilulimeter wave apeefroscopy systems and ccmponents and in particalar to an apparatus and. method for modulating or adjusfin the phase oftbe optical beam directed to the source photonter used in a transceiver fbr tvrahertz spe±osc.py.

2. Description of the ReMed Art

[0003] 1'enhertz devices and systems genenilly employ vlcetrouiagnetle energy between 300 0Hz and 3 teraheth (3 111±), or wavelengths from 100 to 1000 miurnus (0.1 to IM millimeters), which is also referred to as the submi]lirneter or fhr4thared region of the electromagnetic spectrum.

0004] One neportant application of terIherbv systems is Ills spectroscopy Inalrrtz spactroscooy presents many new instrumentation and, measurement applicaon See.eertuin compotmhi iuid objects con be identied and chanctethed by a frequ icy-dependent soiption, chapersion, aad/of refledrn of emhertz Mgnda winch pass throogi or te reflected from th compound or object.

[0005] The generation of.t&ahetzrar-iatipnbyphotomhing is a znãthcd. of geaereting qriasi-optical aignals using an optical-heterodytw converter or photo xer. TioaI photh.rnbcer devices m.1udc low reipcmthre grown (I IC)) fleAs emicondutor devccs which have been used to generate coherent radiatwn at fie.inc1es up to 5 THa. The spL.ctroscopy system typeally uses two single frequeney tunable lasers, snob as. diode lasers, to generate two optical laser beaTn whith axe directed at the surface of the photomixer. By photoconductive mixing of the two beams in ftc seipi.oond.uctot mutethd, a tercherz difference fteqncy between the two optical laser frequencies is geuerate± hr particular, a first laser genente radiation at a first fiequencry and a second laser generates railiition at. a second frequency The difiereucre frequeney equal to the difference between the find and the second laser frequencies, is svept by the user from microwave through teraherta freucnoies by changing the temperature of the lasers, winch coamSy changes The frequency of one or both lasers Other types of tuning roechamsuis rctst noh as disthbuted-Bragg-rflecthr thodc lasers with multiple electrodes, gratug loaded external cavities, etc. A terahertz tn&nsatitter lochides a first photomixer that is c4tibàlly coupled to the ifïrst and the second light suuas A first unbative element or antermi is electricaLly coupled to the' tint photomixet In operation, the first antenna. radiates a teraherlz signal generated by the first phatomixer at the difièrence frequcncy. A receiver includes a second antruina positioned to efy. th thgi. from the tmget radiated by the first antenna. The second antenna generates a thre varying voltage proportiowil to the terohorts return iignat A second phptothrer is electrically cu pled to the second antenna aucfls optically coupled to the first and the second iglit source. The second photoirthier generates a liomodyna downcoaverted current si4 irs response to the time nrying v6ltage generated byth seccm& antenna. The downoonvcrtcd signal is a measurement of the absorption rs reflection of the sample mateia1 at. each tamheitz frequency Na is useful, for example, when used in conjunction with computer processing to ideutifr utowa samples by compadng measured results to a librasy of reference spectra This apparatus may also be used. to Sifacterize the fraqSndy response: (thancteflatics of passive or active companwits acid devices such as waveguides filters, amplifier; mixers, diodes, and the like designed to work at terabertz frequenc lea.

SUMMARY OF TEE INVE&TION

L Objects of flie luventk [000] It. is atu hiect of the present invexdicn tQ proyidq ati improved frequency domain terahqu spectrometer using two continuously tunbin sttuiiconduett,t lwen with the phse oft-ba optical beam spplied to the source or detection photecoSuCiive switch being eleettoulcally modulated oradSustab1e [0007] It Is another object ofthe present invention to provide aterahettz a ct-remoter for the identification oft target speefrem with high resolution and detection senMtity of ahamption bands of interest by producing C'W radiation in one or more frequency bands, and "fine luthng" the terahertz radiation in at least some of those bands to identi(y a spectral signature by phase modulationS [0008] It fs also another obleet ofthe present invention to mitigate the interferunce effect in a ftun3zy dorSia tórah*rtz üp.cthfrmfl.r *1Th fiucily.eortrollab1e phase diffetnec bcweon the nthig hiser beams by parindieatly modulating the phase.

[OOC9] It is also anothe c+jort of the preset mycoton to eliminate the sinft in mtetfereaee patLati's as a result &f movement ci the sOOxej or detector relatre to the target [0010] It is an olj cot of the present invention to provide a method for indepndentiy * tdjusting the phase ditThrence between two source lasers fomAa a composite optical beam used a frequencydpmrdnteaaherlz qmctthneter.

[0011] lit is another object of the present invention to provide a method for adjusting the phase of a laser in a tcrahertz spe&omater using photoconduptive switcbe to provide more accurate freçueucy specificity and recoil rflon by fine tuning" the terahert7 raciiation in a frequency band of interest using a phase inodulatcrr snd a reibrence osdillator f0012] it is also another object of the present invention to pxcwide a tersherjz spectrometer with adjustable resolution of the order cIa M}fr or ItYs of MHz at speeWe frequency banct or abroiplion regions of interest by phase modulation.

[0013] it is another object of the present invention to provide a method for adjusting the phase 0 a. laser in a tereherts spc*orneter usin.g photoconductive switches to provide more accurate frequency specificity and resolution, by fine tuning" the temhertz radiation in a frequency baud of interest (0014] it i still another object of the present invenfion to provide a.self-eonWntd, field portable teithert7.pecLrometei b) 4cm w a hib1y kAinipact cc ration capable of denflf3rmg or rinaging an 3bject ntt2ang a laser with an Scfrorsealty adjustable or controllitbie phase [0015] It tS also anothet obi oct & the present mvenfton to p.i ovido a teranertz spectmnMer wtth adluMabs sesolutwu yf lbt ordt of Mliv or U's f MThr at cpeethc frequeney bana, or alsorptictn rogons of htcst by adjusting the step or nc nent*az ofh frequency sweep.

[00161 it is also another object of the present invendon to provide a terahertz spectrometer with &ljustáMe signal to Oise iatio. of the ordet of' 10 dB Rzto 100 dB-Mz at specific fitquemcy bands or absorption:eglornl f.xittc± by adjustag the time t.onstaut of the lock-in ampb firm j'o0l Ti aTho another ob cot of the present rnventon to pwvide a terahc rtz spectrometer withadjuSble resnbitic,n of the order of MHz or 1.0's of MHz at peciflo tkequeucy biwdo or absorption regions of intexet by adjusting the nterferencc pattern.

(0011] it is also another obeet of the present.iiwen4ion to provIde a terabeit spectrometer with adjusffible resolution of the order of MHz or lU's of M8z at specific frequency binds or absoiptidn regIons of interest by adjtisting the time period over which the sweep takes place.

9 J also another ob1eot of the present mvennon to provide a ter4heifr spectrometer Mtb adjusiable resoithon of the order of MIL or 10 s of Mum at specifiL frequency bands o: absorption 1egions of mtzrest by peifbruuog a phase sweep at a cvmst-u fiequency.

t0020] It s l'' another oh,eot of The present 1nveuton o provide a tenthertz spertrometer with adjustable resolution of tx cider of Mliv or 10s of MHz at specthc frequency bands or absorption regions of interest by adjusting the resolution in the frequency sweep.

[9Q2.] Some hopi meatilions niay sohieve fpwer than all of the foregoing oujeots.

2. Featuret of the hwention Jp022] BSfly> and in general terrue, the uresant çflseiosure prvvidos an apparatus Thi ayzhi.g, identifying pr imaging a target, including first and cecoucl lasers having tmable fraqSncies, the rat laser lo prnduce a first output bem mid the second laser to produce a second. outpTit beam, the first cn4 t beam and. the second output beam having different optieSi frequencies; a phase modulator positioned to moeivp a first portion of the first. oulpirt beam to coutrollthly zrso$uiSe the phase of the first output beam and produdag an modulated output third rain, i tot optical element coupled to the modulated ortput thu-cl beam end to a portion of the aewnd bcau to piochice a composite output fourth beam, a sox'ree ol CW signals in a range of frequencies from 100 MIt to over 2 J.iiz including a first photoconductiw switch activated by the composite output fourth beatn a radiative element coupled to the source of CW signals fhr causing the CW sig$ls to be suhatanttally smmlbneoiisly thoused on orthrouh the target; a ,eeond optical element coupled to a portion of the first beam and to portion of the neord beam to woduta a compozute output IiLtth.beam etid g detector for ac4uiriflgSpeCtXat informrórn uiotn said target anti coupled to f5i composite output fifth hsrn. and generatiag, based on said srectral irrfbrmation and the composite output fifth beam, an electrical signal rnproarnta1ive of a characteiistic of the target (0023] Lu aiiotMr aspect, the disclosure provides an apparatus fOr waly4mig. idemtLdng cm imaging an object, including a source of CW signals with an adjustable phase in a tangO of frequencies greater than 100 MHz directed to saId object; and a detector for acquiring speetul Mthunatiou ctJ acted from or transmitted through sai4 oFjççt and pçzihrming a bete.rodyne down conversion lbr generating au ekctdcai signal inpresentative of some cbzwaeteristic of the object 10024j hi another:aspeot the discloaura providea a method for analying, identifying or imaging an dbject, tholuding enenting CW igtiis' hi. a nwge of frsqucncics lying above 100 MHz utuiiSg a phase modulater with a nf rence oscillator sac!. direetbig the CW signals to said object, end ac4umn spectral Sormahon reflected from or iranntitted through azd obmot and perfomung a heterodyne dowL conversion uscg a 1ock-ur signal flow the ceterence asefflato: for generating an tzleciueal cignal represtatative of some characteristics of the object 0O25] Li anDther aspect, the disciosuic provides a nicthod tar analyzing, rdemtifyinb ot imaging a target by providing list and secnd lasers having list and second quWnt beams respectively having ±f[bnmt frequencies; periodically phase modtñathig the first output beam to prpduc a third beam; generating a CW radiative beam using a fist photoconduelive switch in the range at flequer*exes greutar than 100 M1-12 il-on the first and thud beaw ausmg the CV! radiadve beam to be substantially simultaneously focosed on or through the target; combining the fist beam and the second beam into a composite fourth beam; acquiring a spectral wtoniauon signal from said target wi*rg a second photoconductive switch activated by saur composite fcmrth bearn and generating an electrical signal representathe of a cluiracteStic of said target uimg said spectral iShnuation signal and said oomposite fourth beam [0026] In aSther aspect, the disclosure provides a method comprising providing first and second lasers having tunable freqirnuicics for producing a first opti.eai beam and a second optical beam reapectiveiy with different frequencies; phase shiftIng or modulating the first optical hewn to produce a finely adjirstrtble hise shiftS Third optical beam; producing a composite fourth beam fitun the second and the third optical. beams; producing a composite fifth beam from, the fimt and die. scoond optical besiris; coupling the fonith optical beam. to a first photoconductive switch for producing a CW rarliutive beam Ia a range of frequencies greater than IOU MH; directing the (2W radiative beam to he th cused on or Through a target; arid detecting the radiative beam reflected from or tmnmitted through the thrget by a second photoconductive switch coupled to the composite fifth optical heam and generating an electrical signal reentative of some characteristic of the target [0027] In another aspect the disclosure provides a method fer terabcatr,eetxuscopy including sweeping. a source of CW radiative beams over a range of frequencies greater than 100 MIT; including a first photcconductitt switch aetivated by a first composite optical laser beam; direenug the radiaf Vt team to be ftx,uzed cu a target, and acquhirig spectral inThrmaton from the target by a second pbotocon,dm*ive sttch coupled to a second composite opdcal beam; and adjusting the phase difference between the first composite beam and the second cothposite optical beam by a phase modulator in the path of the first optical beams usedto generate the first composCe optical bean tin generating a&lthontd elecmcal igna1s represcntb of qome chcenstrc of the target in a wlu tee fwquency barth [0028] In another aspect, the dIsclosure pmvides a method for terahe?tz spoctroscopy inelading sweeping, both in frequency and in phase, a source of CW radiative beams in one or more predetermined frequency hsud lyIng hi. a usage of frequencies greater than 100 MI-la; aLqurmg speutral Sotmalon lion the tiget, sad processmg tee.pedml atfonnation to determine the presence, of a specific aDectral signature to ldeidil& a co:mpound of interest.

[0029] The phase moduiatormay be a lithhmi.rdobate mod.ulator [Q03.O] 11* phase moSlatitc. of the OW sigi,ais by the pbas.e modult4c*r wiy result in a consixuaive or destmctive hAtertence of t.be TFIz beam and the compoSE output Mb beaz on the detector.

[003 A signal source may ho couped to the phase mpdul.atur to allow tht first ottbexin to be swept in phase over. 360 4egrees.

[0932] The frequency of the signal source may be selectable to allow the operator to analyze ifi.od ucocy band cfhiterwt.

f0033] The signal source coupled to the phase modulator may ha swept in phase as the first output beam j*g swept in equtnpy..

[003fl A hekrodyne detection may be provided that includes a lock-in amplifier coupled to the detectors wherein the signal warce coupled to thphasemodu1ator is also coupled to the Jock-in.ampilfier [0035] The source c-f CW signals may include a first pbotoconthctfve switch activated by the compositç output fburth beam.

[0036] The first and second lasers may be disposed in a first housing sad the fjrtt photoconductiva switoh may be disposed in a second housing separate from. and spaced apart from the first housing, wherein the first housing and the second housing are coupled by an opticalfibet {0037J The first and aecond lasem may ha dispoand in a first housing, and the detector may be disposed in a third housthg separate from thid zpacd apatt from the.flS housing, wherein, the first housing and tho third bouing are coupled by an optical fiber.

[003$] A.puwer source, kcad, and dispay may he disposed in the first.housing.

[0039] A processor may he disposed in the first.houiug for detennidug a characteristic of the target based upon the absorption characteristics of the target: lix a frequency range in the 100 MTh to nv 2 TIIz frequency bad [004.0] The detector may include a second photbeonductive switch activated by a second composite optical beam from the first and second 1sezs That is offset in frequency from the first composite optical hen [0041] The first and second photoconductive switches may be inw temperature gcwt GaAs ph.otoconduotive switches.

[0042] The first and..second thennocleetric coolea may be coupled to the first and second lasers, rspeet1vely, for independently coarsely tuning each of the lasers over a wavelength range ofahett S am in intervals or step sT,es of thoOt acorn ram [0043] The first and second asc'rs may be DEB or DBR lasers toned to thfièrent frequeneià

I

(0044] The first and second lasers may beatran& cavity Sera * [0945] the first opik3il @iement may be a waveguide coupler.

[0046] The first pbotoconducthe switch may be. bIased with a constant electñcid potential.

[0047] The phase moduistor may be a Etbiwn thubatè device.

[DM81 The signal applied to the phase modulator may be aperiodic 6 kEz signal.

[0049] The lock-in amplifies may be locked to the signal applied to the phase modulator.

[ODSO] In another aspect. tee thacloqucc j>rovde E. method for analynng, Sntrnng or imoging a tatget.compnsmg generathg CW beaths ins. range off pracies lying between 100 MHz to ovcr 2 11Hz; swepiu. both in ft xcy and in phase, the CW radiative beams in one or more predeterndne4 frequexwy bands; dirstbg the ni4intive beams to the target; and acquiring spectral information reflected from or transmitted through the target [0051] Iha CW radiattve beams may be periodically swept in phase aver 30 degrees.

[0052] The acqusifipn of cçentral inmonnation way inoiudc use of a bethrodyne detection system including a luck-in amplifier that is coupled, to th detector and performing a lock4n of the detected signal to a signal applied to the phase modulatot [0053] A signal sorate periodically swept. in phase over 360 degrees may. be coupled to the lock-in ampiffiet [0054] The signal source periodically swept in phase over i60 degrees is swept at a rate at least twien as fiu3t. as the frequency sweeping rate of the laser [0055] The phase moduZtian of the CWradiative beam by a jthase modulator results in an interference Sensitivity, Lu. The detected signal is indqpaet of the distance between the source and the taget.

[0056] The phase moduladon of the CW radiative beam by a phase mbdniaior resaita in the removal of the interft'.renca pattern.

[0057] In another aspeet, the &cloaure provides a method for analyLing, .iden1i1ing or imaging a target. comprising gererating OW signals hi a. range of frequenciea lying bsten 100 MHz to over 2 THz and direothtg. then to the target; and acquiring spectral itnaiionxetkcted from or transmitted through said object and peribrrning a heterodyne down convenion ibr gertemating an. electrical signal representative cxf some chaiactenistica of the *gat.

[00MJ The first and second lasers may have diffarcat tunable frequencies. and wherein the frequency of at least rne if the Sers is swept or mined over a frequency range of at least 0O 0Hz wIth astep size of at least 2GHz so as to produce a awtptCW radiative beam ma range of frequencies lying between 100 MHZ to over 2 THz directed to the. target, and the phase of. the laser is swept at a rate at least twice as fast as the freqaenicy aweeping rate.

[0059] In another aspect, the disclosure provides a method for terabertz spectroscopy iheluding swee$ng. in frequency over a. selactaMe frequency range, a sowea of OW radiative beams in one or more predetennüMd frquenc;ilaads.lyhig in. trange of frequencies greater than MM; acquiring spectral injbrmatlon from the tsrget and piocesthig the spectral infonnation to determine the presence of a speciiic spectral signature to identlt a compowid of nterest.

[0060] In another aspect, the disclosure plovichis a method fbr teraher& spectrosc.opy including sweeping, in a selectable set ci frequencies, a source of OW ndiatise beam.in ona or more predetermined frequency hands lying in a nuage of freqnncies greater than 00 14Hz; acquiring sectxal ththrrnation from the target; and processing the spectral information to fr we of a spe-1 siwture to mdentiI& a comp mmd of interest.

[00611 hi. another atpec the dic1ostfl provides a method for thrahet pecfrosc0y including sweeping, in a frequency band with a aeiectthle step or increment size, a somue of CW radiative beams in one or more pxedetemted frequency bands iyin in a range of frequencies greater than 100 WjHz acquirhig specS information from the target sad processing the spectral mnfbnaatiqñ Ira det inc the presence of a spociiic spectral sigranture to ideotii a compound of in crest [0062] Lu another aspect, the disclosure provides a nethod thr terahertz spectroscopj including sweeping, in frequency over a selectabie time period, a source of 12W radiative beams in one.or uxare predetermined frequency bands lying in a range of frequencies greater thaa 100 MW, acqming spccfl! roftirmdion frum the tsxget and procesmg tie sptrfrdl «=nfotinatiott 10 determine the presence of z specific spectra! signature to identii a compound of interest.

[003 In another aspect, the disclosure provides a method for tenherly spectwscop including sweeping, in a frequency band with a seectablcresohiti.o; n source of 12W radiative beams ira one OL more predetermined frequency bands lyIng in a range of frequencies greatr than Mu; acquiring spectral information from the target and proce hag the spectral information to detcrnine the presence of a specific spectral signature to ideatifiya oompouufi of interest.

[0064] Lu another asptct. the disclosure provides a method tot teaheth spatrescopY utclu&g sweeping a source of CW radiative beams in one or more predetermined frequency bands lying in a range of frequencies greater than 100 M11z acquiring spectral irthrnxatthn from the target; and processing the spectral inffirmatio with a lock4n amplifier with an adjnble time constant to.determite the presence of a specific spectral signatpre to idcntifr a compound of interest [0065] k another astuict. the disclosure provides a cuthod fot teMtrtz xclroscopy including &weepmg a source of CW ndiatjve beam ir. one a more pteleteumued frequeacs bands Iing in a range of frequencies greater than 100 MUz acquiring spectral wherein information from the target; and processing the pectrth infonnation with means for adjusting tim nnerf'trence pattern to determnz the preseit. e of a specific spectral signature to dentfy a compound of interest [0066] in the sweeping process, the step size may be selected by th user to a selected vaiue as an. eampk, in some embodinients, to a value between 100 MHz to S GUz.

f0067J In the sweeping process, the number of 1±equeSes may be selected by the user to a selected value, as an example, in some emhodhnents, to a value between 100 and 20011.

[OOÔRJ In the sweeping process, the time pe1od of the sweep may be. sejected by the user to a selected value, as an exam$e; in some embodiments, to a value between 10 seconds and 1000 secourt;.

(0069] Ihthe sweeping process, the slap size, the number ofticquencies, and the time period of the sweep. may be adjusted to achieve a given resohxtiou end signal to noise ratio.

(0070] Some implerneotthions or embodinerS may incoiporate or implement fewer of the apets or featurta noted in the foregeing eururnaxias.

00711 Additional objects, dvantages, and noc'eJ feature' of the present uxeatcrn will bcwine apprectto thosa skilled in the sit from this tha.Aos it. c1udmg the thU owing detailee description as well as by practice hf the inventiort. While the invendon is described below with re*rence to preferred embodiments, it should be inderatnod. that the.inveixticn is not limIted thereto. Those of ordinaiy skill in the art having access to the teachings herS will recoize addthonal applications rnodifii thons and ernix dimeats in ohei fie'ds, which are within the scope of the invention as d!%Ioied and clidmed. herein and with rspr.ct to which the htveutiou could be of ttti1it.

BRIEF DESCRIP liON CM? E DRAWINGS [0072] These and th.er feahrra iind advantages of tb( invention will be better understood and inure.frlIy appreciated by mftrence to the following detailed descriplion when ( >wdered in cojuncthm with the accompanying drawings wherein: [0073] FIG. IA is a block diagmm of a frequency domain tershertz spectrometer acconling to the present disclosure which employs reflection from the sathple; [0074] PTCL 113 s a block diagram. of a Lteqtxeucy domain terihertz spectromeleraccording to the puisent disclosure which employs transmisiOn from the sample; [0075] FiG. 2 W a block diagram of a frcquenc7 domain tenher& spfloineter of the

present disclosure; and

[0076] FI& 3 is a block diagram of a heterod ne detection system subassembly.

[0077] The novel features and characteristics of the disclosure are set forth in the appended

F

DEl AJLLD DEsrairnoN (lB THE PRPEERBED EMBODTh&FNT [00781 Dtiis of the pmsett diattiosure will now bt describeth includrng exemplary aspects and rmbodiments thereo Refeumg to the dmwtng' and the Jbllosisig descripton like reference nurnocn erc ued o dentli like or junetmually simriai elements, and are ntended to illustrate major ththres of exemplary embodj±ne3ils hi a highly simpliüed diagramrna8c nrsnner.

Moreover, the thawing are not intended. to depict cvery feature of actual embodiments or the relative dimensions of the depI4ed elements, and are not drawn to scale.

[0079] Reference throughout tIS specification to "one ewbodhnet" or n erx3bodin6nt means that a particular feature, tiructure, or pbaracteristic described in connection with the embodiment is inekided in at least one embodiment of the present invention, Thus, the appearautea of the phrases "hr one ernbodtnent" or "in an embodiment" in various plates throughout this specification. are nest ziecessnrily 41 rtferthg to the same embodiment.

Futhiexrmre, the parttcular fethxrcs, tnctures, or chsracthc sties imy be combmed m any suitable manner in one or more embodinientL [00801 As noted aboe, u the frequency domai tcchmque c,r tei ahert7 pecAmsco1y, CW Tflz rathahon is produced through phoromixmg of the combined output of twA mgie4zequeucy diooe lasers in a low temperature growr (mA5 phatoxrtr or PCS The wavelettgth of one (or both) of the lasers is tuned by temperature adjustment of the laser to coarsely vary tire 1hz output fequaney, tch may themibre be swept over one ormore frequency hands ofinterest for characterizing the targetor ampte material.

(00811 In most frequency dc5m&n spectrometers, coherent. (homodyne) detection can be achie*d at room temperature by rni*ing the same optical radiation from the diode lasers in a detector PCS. onto which the Mnrt TTh signal is ilso mmden±. This wo-'4 similar or greater sensitivity ad fster data ac sition than. the incoherentteehthque.

[00821 In o teralttz speaometer. the terahfl radiation Ia focused or 4ircted to the target sample to be aniyzS, and a detector or detector array is atmuged to collect the sigeal propagated tbrongh or reflected from that target The two modes of iwisruiSiori, or reflection from the target aTi illustrated in flG IA and IS. The conligeration or arrangement of F1G lÀ depicts reflection, and IUG lB dej,i 3taismission thumgh the iarget o sample by apprepriate placement of the sourcc,bead or module 201 and the detector head or module 201. A housing 100 @thovm in FIG. .2) iueoiporaS the user interface and the optical smI S:trO)tic31 components associated with the coupled speotrçnxetex heads of FIG. IA sac! It Ta One &ubodimeut of the present disclosure, the modules 201 and 202 a,enplod in different housings, each cf which may be manually moved or positioned by the operator with respect to the sample under test A *flbar optic cable 117 and an electdcai edIt 217 couple the housing ICC) to the niodu Ic 201, and flbc optic oabk 118 snd an electrical cdblo 215 couple the housing 100 to the module 202 The silicon lens 205 on the exterior of the housing 201 enable's the terahertz irdiation to be focused or dutctcd to the target by the awl the tbwi1 lens 208 on the ertener of the iousng 202 is positioned by the user sa that it cd1je' ta the radiation transmitted or reflected from the target. It is noted that additional optical elements including but not limited to lenses, focusing mirrors, parabolic reflectors. sub-reflectors. bearnsn1itters/combiners, and bearnshaping optics (not shown far clarity) may also be etployed puvida focusing or thpulation of the radiated terahertz beams, as the particular measurement siku lion requires [0083] nc. In is a block diaarn of a representive spectrometer arranged to employ frensnIL4SiOn through the sampie The opeEatipn of the various tompt)uent9 are substanliafly identical to die opeiation hi PIG. IA, and need not be rcpeated here. Tht figure illustrates how lIe soutcçt and detector housings 201 and 202 may be mamially moved and posin ned by the' operator with respect to the target. Alternatively; the source and detector h.orrtgs 201 and 202 may he combined into one common boutg.

[0084] Turning to Pf C. 2, there is depicted a housing 100 incorporating the optical and eleciro'-opticai oornponcØs ai1ted fbr ase as a subassenibly in conjunction with the coupled spectrometer heMs of FIG IA anc 13 In t.ome embodimeuts, the housing is sized and desIgned to be lightweight and portable, and worn or.uppoited by the user during operation.

Laser sal saemblie-s 101 and 102 Include lasers 105 atit 106, respectively, which are preferably twO 783 n distdbtited feedback (DFB) or distributed Bragg rct)pator (PER) seadeonductor laser diodea with ahsgie4oagithdSLmode and single spatial-mode operation over the desired range of wavelengths, available from various vendors (for example, Eagleyard Photoltics OnibE of &riin Gennarm or Photodiwn, Inc. of Richardson, Texas). h some embodiments it would dsc hr. possh1e to utd ze one or mow packaged ertemrd-cavity tunable qenxconductor lasen, are Ya3lat3le fi cm Itmeore C cporaton, of Newark, CabThnua, suab as chclosed in Ii S Patent Application Serial No 1 u/722,82, tiled March 12, 2010 In one anbodiment, the output of oms laser is adjusted to 783 ran, and the output of the other laser is adjusted ft> 784 inn. The diode laser packaging 1entts ce-collimation of the laser bearu to a very high degree of precision, ant the design allows very precise frequency control of the lasers by tnmperature aztdlor etectmme tuning, earl monitoring the laser output through digital signal processing, to achieve more acenrate control. over the laser output beam fieqrencies.

[DoSs] in one embodiment, the laser diode chips 105 and 106 are mounted on iadeçendent Peliler thermoelectric coolers (IECs) 103 an4 104. The center wavelengths of the lasers are nominally 7R3 inn at 25°C. hut the. wavelengths may be coarsely ternperatnte-tune4 With a tuning coeflicicot of.aayproximatefy 0.1 nra. per *(, Therclbre, a 50 degrez C tempeninre range of operation from -10 degrees C to -40 degmes C will yield a frequency range of anpro*im.ate11 1 urn. For the purposes of fflustnttic'u only, if the DFB iSers are selected such that theft center wavelengths at 25 dcgr&es Care at 782 urn atd-74 tan, respectively, then a thermal tuning range of --40. degrees C to 4-40 degrees C on each. laser chip will pennit genezation of offiet wa ckngths 0 nat to approxunately 7 urn, eonepondmg to a range of ofihet frequencie from 0 Hz to 14 Tha The thennal mass on the controlled, surface of the TECs is such that it állo*s rapid fiequency tuning. In the ease of D3R. laser diode chips, the BraggrofIection section of each laser way he adjusted electronically to vguy the laser Wider-offSt terprerroy ranges may also be possible by employing wider temperature excuralo; or by using DBR or external cavity lasers.

[0086] The output beam f on each laser 105, 106 is collimated with an aspheric lena 120, 121 respectively mounted on a precision lena-mount with sub-miami adjustmeut capability (see, e4-U.S. Patex4 7,126,078). AThrr passin&. thEough the lens, the laser output beams are directed.

through, a. respective optical.isabdor 122 and 123, to prevent feedback into the laser, and.to cinple the output beam tg pigaii optical fibers 107 and 108, respectively.

[0087 A 50/30 waveguide coupler or beamaplitter IBSI and 1382 axe coupled to the pigtail optical fibers 1107 and log, respectively, and the output beams on fibers 107 and i08 am each split.into composite primru-y and secondary beams. 109 and 110, and 111 and 112 respectively.

[0Q81 hi the en*odixuett depicted in the present diseSure, the pthmafl' output beam 109 is directed along a Iibcxr or th'at path. to aphase control clement: such as a phase modulator 113. The phase modulator 113 may be an lithium niohate device, auth as those manufactured by Photline Teebno!ogie of Besancon, France. The phase modulator 113 alktpiwthe user to sweep the phase automatically (by pre-programxn.ed aoftwart or manually adjust the phase otthe bs* output beam 109 in a 1dbi precise manne, thereby slap adjusting the phase of the ainItted CW terähertz beam. The output of the phase modulator 13 is then coupled to awaveg'aide coupler or heameombiner BCI. In some embodiments, the signal applied to the phase modulator is a periodic. 6 kffz signal, or more generally, a periodic signal that is swept at a rate at least twice as that as the rate at which the laser frequency is swtpt [X)89) A tunable rthrencc oscillator I 14 is connected to the tbase modulator 11% tbr sweeping or. precisely incrementing or decrementing the phase by a periodic or other type of signaL f0090) The beam 111) is dlirected along a fiber or first path to a veguide coupler or beameombiner 1C2 and similtrty the beam 112 is directed along a fiber or first path to the wave-guide coupler or heameombiner)3C2. The hum bcmsp1itter BSZ. is directed along a fiber 118 er twa path o as toexit the module 100 and i subsequently directed. by fiber 118 to the deteckrhead2fl [0091) *fhE output beam 111 from bea-rusplitter 1382 is directed, along a fiber or &*t 1atb.to the be recoulbirtr ECL. the output of the phase modulator 113 is clin3cS along fiber 11.6 to the beamacombiner BCL Theomttprt of beamcomobiner BC1 is then applied to fiber 117 which exits the module 100 and is subsequenily directed to the scan-ce head 201.

[0092) The optical uropagation path downstream of the lasers and thrpughout the unit 100 may be an appropriate single-mode polath.ation-mthutainiug cptical fiber (PMF) or free space.

In the case of optical tibet consiruetion, the beanaepilflen may bç replaced With suitable optical wavcgmrle L)uplem Ai can be appreciated, the basic topology cteptcted in FIG 2 Uses tier optied implemeutation which readily iflu*ates the vañous optical paths, while fl& 4 Will illusirate frec space. implementation [0093] The beam from hearneombhier BC1 is coupled to a fiber.117 which jathen coupled to the external source head 201, as described above. In source heed 201, the composile output beam Of the two distinct laser sources is then applied to a lens 203 which focuses ffi beam to a apot of approrimately teti microns in diameter on the surface oft low temperature grown (LTG) gallium arsenide (GaAs) photcoonducive switth. (PCS) .204 The to optical bean are GOWMRe(I at 1hotoirdxed in IJ?CS Z04 Other lypes of photoconduetive switäbes.may he. used as w4l.. The.laser beam may be thoused at a gap in an efteult petterned on the surthee of the PCS, Width in some embodimeuth is binpiemented as the spiral as shown in FIG. 2, with thØ gap located at the canter of the spifal. A constant DC electrical bias coupled to the source head by cable 217 may alse be applied acnas the terminals, of the antenna on the PCS. bit nrne I; embodiments, as known in the prior art a slowly ti e-var3ng (i:t chooped") electrical bias F sIgnal may be applied across the terminals of the antenna on the PCS.

[($94j The 1eribertz variation in the irtensity of the mixing or difference 4unl betweca the two laser frequencies, often rcfenitd to as the "hettrodyne laser.aignai" produces a teraheth modulation of the contottuice} the ?CS materiaL which in turn produces. a terahegtz entreat flow in the anteatia patterned. on the b1nfäce of the 3..CS. This cutrerxt In. the antenna produces an electromagnetic field, he. tezahorbr radiation, propagating into the sunnunding spaee and having a frequency range from typreafly 100 Mb& to over 2 TilL. depending on the difference frequene of the two. laser scurcet The terabertz radiation so produpd is emitted from pcs.daitt 204 and then. coflinated and collected by a silicon kas 20S prafisnbly a hernisphencaily ahtced *uctute appro,±oatSy two to three ccotineters in diarn*r Additinnal lenses (not shown).

composed tIThFLON1M or other suitable materials may be placed downstream of the leus 205 to colihe e the RF beams into an. output terahertz beam. Beam-shaping mirrors may also be used in lieu f or in addition to silicon lens 2G5 hi the source head 201.

[0095] Th outgoing terahatz radiation beam from currently available PCS devices is relalively low power, about 1 to 10 ndcrowatts. The target auple (not shown) is tilc&1y positinned relatively close to the source and detector heads, and will absorb and transmit some ierahertz radiation, and atso reflect a portiat of the tarahertrradiation back in the direction of the source or use?, as shown by the return flfr hSn Ia FIG. IL [0096] On tb.e receiver side:f tie spectrometer, the beam from heamoombiner BC is eccipled. to a fiber 118 which is then coupled to the external detector head. .02, as desedhed above In detector head 202, the composite output beam of the two disthict. laser sowees a then applied to a lens 205 which focuses the beam to a spot of approänately ten microns in on the sutface of a low teirwexaiure grown ([TO) gaThum arseinde (GaAs) piotoconductive sWitch (CS) 207-Th.e two optical beams are combined or photomixed in the PCS 207. Other types of pbotoconducthre switches may be used as well. The laser beam. may be focused at a. gap in an antejxoa circuit patterned on the sufface of the. PCS 207. wiuicb in. trnme embodiments is impkmented as the spiral as shown in FIG. 2, with the gt located at the center of the spi.rai hi some ea bodiments the spiral axtemia on the 4ctector PCS 207 is.anpleinemui ni a clockwise direction, in confrast to the counter-clockwise direction of the spiral antenna on the source ItS

I

{0097] Ihe terabertz return siai from the ieirapl* or tsrget is cptwed by a suitably positioned second dice lens 20$ itt. the detector head ZOt, which ftnruses the return terajie.th beam to the antenna on the surface of PCS 207 which acts; as atenthertz radiation detector (0098] In the prior art embodiments, the terahertz vadalirso itt. the intzTsity ol.. the mixing or difference signal between the two laser frequencies, in combination with the teraisrtz modulation of the conductance in the PCS matethd, as a resz1t of the temhrtz eusrent.tluw in:the antenna from the received terahertz signal from the sampl; remd4 in a homodyne down conversion of the received terahertz signal to a lxwebnnd frequency equal to the "chopping" frequency, that may then ho detected by a aynchroneiis circuit stcli as a "iocic4tf' amplifier, or sImilar arrangenent 00Q9) hi embodiments ccmtemp!ateti by me Fesent ittclostre. the teiaherz sanaton in to tol.cwnty of the mixing or diffeierce zigwfl betw...en the two laser frequencies, in combination with the tenthertzmodulaUon of the conductance In the PCS material as a result of tht tet'ahertz cuineat flow in the antenna from the received terahertz igna1 lion the sample, tesu3ts in a haterodythug and dawn conversion of the received terahertz signal to a baseband frequency equ to th1 equency of the reference oscillator 114, Th &ynchrwtous detection circuit makes oscillator 114 signal applied to the phase modtor 113, and theiby to the signal applied to source PCS 204 na a refetence br the synchronous detection proc*ss [OOiC'Oj A signal resulting from this heterodyne detection system 209 may he coupled to and processed by processpr 210. The ilrom.etec may further incorptuzt. oftwae for aut,tnatically drcterrcining the identity or nomposition of the target, and other electronic elements for pthting or displaying the results s'o that the analysis, identthcabon, or image irifomiation is readily available to the neer. FIC+ 2 Hiustraie a, communicatIons. interäee (which my he a wixiess 1ff trsn'acáver far connnumcating the results. to en external user or networic element) 211, a display 212, and a keypad 214 as tauples of elements providing user or operator inteithee, A battery 213, or other self-contained power-solute, may be provided, to make the unit

field poftable

[OU1QI]* In one embodiment, the frequency of one of the lasers, aM consequentially the radiative tertherta fh4uncy, is swept or timed through a series of-frequencies, or thxuugh a sequence of distinct pzcitIc fteqaency bands The retims teraheilz signal S is collected by the detector and fraosfrrsed to processor 21(1 for data collection and analysis at each specific frequency of nwre0t In tb1 wn the absorplion or rsflectin spectrwn of the scmiple wider test can be collected with high resolution 0nd nigh signSto-noie ratio q'nee all of the terahertz energy is centered in a single tone and the luck-in amplifier lImits the noise bandwidth. This, incidentally, is a major advantage of the frequency domain technique compared to lIme-domain.

teelmiques in wi:dch the terahertz energy is spread over many frequencies. in some embodiments, the tuning and tor-abcriz.emissioti miy. he adapcd to a specific jtience or act of frequency bands having spectral absorption peeks toaesponding to the unique spectral sgcatuxe of a paxticalar material of concern. Thus, the frequency sweeping tie may be minimized if the user's application was solely the question: "Is compound X present In the sampid?", toe the processor aid software in the spectrometer may he pre-propamrncd to only genemt; sweep, record and analyze the terahfl frequency hands associated with the snectral sigesture of a pathculermaterial of ounce-rn..

[00102] FIG. 3 is an. enlarged block diagram of a heterody e detection subassembly 209 shown in nc. 2. The reference oscillator 114 provides a iefereic sigpal that may be adjosted h' the operator bctweeri.9 nd 1.0 Olt ic sejectable. step tact. üdervals ranging from 1 Hz 13 1 GB? the rgnai tom the eet"ctoi N'S' tc applied on hue 215 to a mw notse mph fir (LNA) 301, and thee. io.a synchrcnous detection eizuit 02. the downeonvated outptLt of the synchronous detection ciictht 302 is then forwarded to the pwcessor 210.

[00103] In summary, certain aspecth uf the present disclosure may pawide a compact frequency domain. rerahertz coherent apectrometer mith either confinurnis tuthng, or discrete ti3mng within certain identified frequency lxmdi greater than 100 0Hz. $ucb cowthuctiou may employ highly compact photonic integration techniques, and roorn-ternpeszbare coherent THz detecdon. Adv geously, such devices may offer rapid identification of chemical,, biological and etpIosive materiaLs in both the soi4-pbnse and tim ga&phaw at siandard atmospheric pressure. Some embodiments may atilize a highly htgrated hotothc assembly cmapoying semiconductor diode lasers employing no moving pn, . it is itherertiy rugged and we1l suited to fleiddevloyable applications. The tquencyblfled optical beams are incident on the at irce tCS er alternatively, in other embodiments, the detector PCS, or both), and provides a means to effect c:ctremeiy high-tesohttion. spectroscop. Typtesi therroal tuning resolution, and accuracy of the source lasers may perfbrm coarse tuning oS awave1engUz range tçp tU7 urn, in intervals or step sin of amer than 000I ma.

[001041 Ot..course, vedous modifications and improvements of the preseel: disclomnc may also he apparent to those of ordinary skill in the art Thus, the patticelar cornbStior& of wtth described and ifinstrafed herein is inter ded to represent only certain ombodirotrots of the preeut invention, and is not intended to sen'e as limitations of alternate devices within the spirit and scope of the invention.

[00105) it will be understood that each of the elements described abtn; or two or more together. also may find a useftil applieslion in other. lypes of conscruadorw. differing froth tht types described above In picalar, certain, configurations presented according to particular aspects of the present invention have been Shown and described us discrete elements, ie., 1asrs, spititen, combmers mirrors, lexisec, hffiers, fiber optical cable, et Those skilled m the art wth readily npprethate that many or all of these individual, discrete components may be thbricated andiDr packaged into integrated thements. By way of particular example, the use of integrated waveguides and associated structurçs is e: sioned for the described. structures and axrangemsrd& Altariativeiy, The discrete elements, is., lusors splittea,. combiners, ntizmrs, lenses, shifters, etc. may Sc be thdividuailypatikaged in modules with optical fiber nter3onnects to achieve the same topology and fimctionality.

[00106] While the present disclosure ifiusturtes and deseribes a tcrohexta segiver or spectrometer system, it is not intended to be. limited Ia the details shown, slice various inodjicatriuc and stnrcturril thauges may be made without deparbag in urry way fr&u the 5pnt cif the present tnvethon, [O0l07j Reference throughout this specification to "one embodiment' or "an embodIment" means' that a particular feature, structur; or characteristic described in connectic. . with the embodiment is ioIided in at least one embodiment of tire present invention, Thus, the apparancen of the phrases hi one er,bodiment" or "in am en$d.ment" i. various places threughout this spcitcatkw ere not necessarily all referring to the ucrue embodiment.

Furthermore, the particular fbatures, structures, or characterSes may be combined in any suitable manner in. one or more embodiments.

[00108] Th.t forqoing described embodiments dpict differen e-,mponaits cflineA within, or connected with, different other compoients. It is to be underatoM that uch depleted arrangements or architectures are merriywwmplaiy, awl that in fact many other arrangenent.z or architecthres can be finj iexnented áich achieve the same fixuofionathy. in a conceptual sense, any arartgement.01 componenS to gdieve. the axne tbndionnlity is effeothely "associated" such. that the desired flmctionelity is achieved. hence, any two components herein coabind to achieve a particular tartcbonahty can be seen as "assocntect with Sob other such that the dodrcd fim.eUonality is achieved, irrespeethe of specific slnzctote; architectores or iatemiedial compnnentb Ltwis; my two componecta so associated can also oa vecs ed a bemg oL1er>Jbly connected" or "operably corcpled" to each other to achieve the desired ftncdonallty 100109] Wbilt particular embodiments of the present ftwer.tion have been shown and described, it will be understood by those skilled in the art that, based upon the teachings hesS, changes end modtfieatic.ns may be made withcnd departing from this inverinon and its broader aspects and, tbereføt, thu appended claims are to encompass within their scope all such changes and. noditicaffons as are within the true spirit and scope of this. ix&vetifioa Furthermore, it is to be urderstood that the javention is seth. ly defined by the appn&d claims It Qvdl be,indertood h) those withm the art that, in general terms.sed herein, and especially in die apperiJed clauns (e.g., bodies of the appended claims) are generally intended as kpnn° tents (e.g., the term "including" should be bteipteS as reiiig but upt liSted to? the term "haing' should. be intezprete4 as "having at 1éSt, the term 9nclud& should be intepreted as "includes but is not limited to," Sreonjae and variathrns. thereo4 such, as, "cornptises" and compdsing" re to he ecinstuied in an open, incusive sense, that is as iuciuding, but not llrnited to," Sc.). it will he ifirther understood bt those within the art that if a specific number of air introdeced claim reettafion is intended, such. Si intent will. he expioifly recited in the claim., SId.in the thscnc of.

such recitation no such intent is present For.ctarnpla, an aid to mdetstauding, the following appended claims may contain usage of the introduøtary phrases at least on&' and one or XEIOr&' to hitwdune claim recitations. Elowevar, the use of such phrases sbeuid not hr construed to imply t$at tim intxodimtion. of a claim recitation by tfr indefinite articles a" or ant' Unit, any particular claim containing such infrodueed chuin recitation to inventions coiiSximg out' one auth ieciLaticti even wben the same claim includes the introductory phrases "or!e pr mor&' or "at least one" and indefinite attlelea such as "a!' or aif (e.g, a" sndThr "an" shou1d typically be interpreted to mean "at least on? or "tne or rnorp the same. holds true for the use of deftinta articles used to introduce claim recitation In addition, even If a apeetlic number of an infrothiced claim recitation i explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean lit Sat the recited nmnbcr.(C,g, the bare recitation two recaeuons," withou' other moditian, typically mrin' at 1cat two trntfli tq, or two or more recitations).

(00110] Withrnx{ further aLayis, from tim ioregong ohen can, by applyn'g current 1mu*ledge readily adapt tue disclosed technology for vanou appbeshans Suh adaptatons should aim are intended to be comprehended within the meaithug and range of equlvalence of the following claims.

I

Claims (5)

1. Wiat is ekdrncci 1. An apparatus for. anaiyzinj, i.dcntfyiug, ox imajng a target, said apparatus comprising: first and second lasers having tunatle frequencies, said first laser to produce a first output beam and said second laser to produce a second output beam. said first output beam and a&i second orriput beam having different frequencies; a phaM. modukitor posi1ioied to receive a first portron *u said fin* output beam to controllably modulate the phase of the first output beam and producing an modulated output third beam; argt optical element ecnrpl.ed to the modulated output third beam and to a portion of the seconi basni to produce a composite output fourth. baanr; a source of CW siguals in a range of frequencies from 100 0Hz to over 2 THz including a first photeconduclive switch activated byte composite output fouxlh beam; a rachatne element enupred to the sane of OW signals far ausmg the C'Y signals to be substantially simultaneously focused on or through the target; a second optical element' coupled to a portion of the first beam and to a portion of the send beaM to produce a composite output fifth beam; a detector fur acquiring spectral inthimafion. from said target and coupled to the composii output ftfth beam, and generating, based en said spectral infotnation and the compusita output filth beam, an olecthcal signal mtrresentativeof a tharactcrinfc of the target.
2. 2. An apoaratus as defined in tlairn 1, wherein the phase medujator is a Iitbfiwi.thabate madtiiatut..
3. 3, Au rq>paratus as defimed in cI* 1 ctherein the phase modulff on of the C:W.igols by thç phass modulator rasl.tlts in a construotive or destructive interference af the Tftz beam and the cqznppsite output fifth heath on the detector.
4. 4.An apparatus as defined in claim i thrther comprising a signal source conpied te the phase modulator to allow the first outout hasm to he swept inphase over 360 detjrees.
5. 5. An apparatus as defined in claim 4, wherein the frequency of the signal source is selectable to allow the opcrator to analyze a pebifkd frequency band of inferS, 6 An apparatus as dci9ned rn than 4, therea the szgruu,otirce coupled to the pb ese modusot in swept in phase as the first output beam M swept in freipency.7. An apparatna as defined in ilaim. 4, further cuniprisng a hetenodyne detection system including a look-in amplifier coild to the detector, wherein the signal source is coupled to the loOk-in am$ifier.g, An çparatns as defmcd in claim 1, wherein f& onrc of CW signal' includes a phutoconouctive switch athvatecl by the to nposrte ontpu fnzth l'ea 9. An. appsrata as defined in claim i, whetS the first wd second lasers are di%posM in afirat housing, and the first photoeondutkVe swith is disposed in a second housing separate from and spaced apart from the first housing, wherain the first housingod.tba seeonA bousirgare conNed by en optletd fiber.10. An apparatus as defined in ciSt 9, wherein the first and second lasers are disposed. in a first housing, and the detector is disposed in a third lions ing separate finm and spaced apart from the first housing, wherein the fint housing and the third housing e coupled by an optical. fiber.ii. An apparatus as defined in claim 9, thither eompdsing a power aource, keypad, and display disposed.ia the &s housing.12. An apparatus as defined in claim 9, thither comprising a processor disposed in the first housing for deter th g a characteristic of the target based upcrn the absoi!=on characteristics of the target in a fraqrwncy range inthe 1.00 0Hz t over 2 1Hz frequency bau.& EL Arj appntus as detined n ciaim 8 wherein tho detector inebides a second phothccrnductive switth activated by a second romposite optical beam. from the first and second lascre that is offjit itt tit.quettey from the first composite optical beara 14. An apparatus as defined in chum 13. wherein the flnlt iud. second photocondnthv.e switches arc low tcmpexntur grown GaAs photocooductive switche.15. An apparatus us defined, in claim. 3, further comprising first second thermoelectric coolers coupled to the first and second lasers, respecthay. for isleixtdently coarsely tuning each of the lasers over a wavelength range of about 5 urn in intervals or step sizes. of about 0.00 01 mu.16. An apparatus as defined in claim I, wherein the first and second lasers are DPI) or DBR lasers tuned to different frequceSs.17, Au apparatus as dethied. in claim 1, wherein the first and second lesera are external cMty 1asers 18. An apparatus as defined in claim I, wherein.the first optical eJement is a waveguide coupler.19. An çparatus as defined hi claim I * wherein the first photoconductive switch is biased with a constant electrical potentiaL 20. A method fbr analyzing, identifying or hnagIug a trget, comprising generating CW signS in a range uf frecpieucies Iyizg between 100 GFIZ to over 2 1hz and directing thea to the target; and acquiring spadral intbnaalion reflected from or iinamifted through ssid.cftcct ad perfonmng a betarodyne dowmnnversion for generaiang an e1eotnc signal repra ctattve of some clmractedstics of the target 21, A method as defined in claim 20, fbrther cornpthirg providing first and second lasers having different tunable frequencics, and cfierehi generating CW sigmils includes activating a first photowrkluctrve 4wLtch by a fS coniposde optical beam flora te first and second lasers and vryhg the phase of the first composite optical heim..22, A method as dtine& in claim 2!, thither comprising providing first and second lasers hiving different marthie frequencies, and wherein the frequttioy of at Sat one of the lasers is vçpt or timed over a frequency range of at kas4 00 Ol-r with a sttp size of at least 100 MHz so as to produce a swept CW radiative beam in a range of frequencies lying beeo. 100 MHz to oer 2.1Hz &eoted to the target and the phase of the laser is swept at a rate at least twice as last as the frWnC3T se.epirig rate.23. A method as dgtthth in cialin 22, wherein the b*1yue do c vcrr&ni iaohtdes activating a second photoconductive.jwithb by a secoud composite optical bean from the first and second lasers that i cfThet in thquency from the first optical beam.24. A method for analyzing, identifying or itnaing atarget, couwiISg: providing that and aecond lasers inMng first and second otitput beams respectively having different frequ.encis; phase mothiladng the ffist outpat beaw to produce a third beam; generating a CW radiative beam in the range of frequencies from 100 GRz to over 2 1hz flow the cond and third beams; cawing the CW radiative beam be aubstanflaib' simultaneously theused on or throngh the targcq combining the first betm an4 the second beam into a composfle feufllt btw.th; acquIring a spectral inf<irmation aigna1 from said target using a second photoconductive switch activated by said composite fourth beam; n'x elecincal sgual repnsantatve of a characteristic of said tngtt using the mtercetence pattern generated 1mm the pctra mthrmation siwal and the coniptsite fourtb beam.25. A rmthod s in dan 24. thrtber comprithag Qonirollably adistbg the phase rnodulaon of the first output beam to as tc modify the intextrea9 patten over a sele*tt&1 raege of freqowdies.oif the CW radiative beam.