GB2511242A - Terahertz frequency domain spectrometer with phase modulation of source laser beam - Google Patents

Abstract

A method and spectrometer for analyzing, identifying or imaging a target comprises generating CW signals in a range of frequencies between 100GHz to greater than 2THz and directing them to the target, acquiring spectral information from said frequencies interacting with said target and performing heterodyne down-conversion 209 for generating an electrical signal representative of some characteristics of the target. A lock-in amplifier at the CW signal modulation frequency, from phase controller 114, is used for the heterodyne detection of the terahertz signals.

Description

REFERENCE TO RELATED APPLICATIONS

[000.1] This application is a eonLinuütion-in-pafl of US Patent Application Serial No, 12861,651, flIed August 23, tO3, which 11 two is contrnuaion inpat1 of US Patert Applu.auon Srial No I2162i9, filed Mtiv 13, 009, now US Patent No 7 ?81336, ssEuth ?Iphcatk)n claims priority of US. Provisiom,i Application SedaiNo. 611054,344 filed May 19, 2008. Each. of these applications islherëin. incorporated byreferencein its:entirety..

BACKGROI.MD OF THE INVENTION

L Field of the inventioi

[Q002 Tie nnention *elate, tO nh{cIo'y\a've, ITh ilmetci WdVt and stibmiflimetw 4\'t spectroscopy s'stem, ard outponcnt, 4nd m PthUr W an appauus aud nctnoct fo modulating adiusthg the ehase of the optical beam ditected to the soutce phcto.mtxer used in a transceiver for terahertz.spcctroscopv.

I2. D1ecription øf the RWatedAtt [0003J TCrahertzdevic.es and systems generally employ electromagnetic energy between 300 0Hz and. 3 teraherz (3 THIz), or wavelengths from 1100. to 1000 micrOns (01. tol,0mii1ix ietCrs)., which is also referred to as rho stsbmillimetet or far$nflarcd egon cf the electromagnetic 5pectrtlm.

[0004] One importam application of tcrahertz systems is THz spectroscopy. Tetahertz spectroscopy presents many new instrumentation and. measurement applications. since cain compounds ate! t)hiecis çaji be ideplifled. and characterized by a ftequcncvhdependent absorption, dispersidu, and/or reflection of terahertz signals iich pass ihrougji or are reflected fton the compound or.obiect.

[O('O5 The çcreratior of tcaherU achanoii by phctoni xnig o a methoc of generating qJasl optirid sgnais using an opticai"heterodyie converter or photoutixer. T3tpical photomixer devices include iow-ternperature-gro.wn QTG) Ci aM semiconductor devices., sshieh. hae been used to gci.erate..oucrent adiauou at frequencies up to 5 1Hz The spectroscopy ysteir typically uses two smglc frequency uvahk lasers such as Jtode bscrs, to generate two optical aser &am 4iich are directed at the surface of the photomixer. By. phutcc.onductive mixh'tg of the two bSms in the sethiecnduttOt. maerh1, a terahdrtz difference frequency between the two optical laser frequencies is generated. Lu particular. a first. laser generates radiation at a first requencv and a..secon.d laser gen rates rad.tat.ion, at a second frequency, the nifference frequency, equal. to the diff'éttnc;e between the ffist and the second laser fItquencies,. is swept by the. user from microwave through terahertz frequencies by changing the temperature of the lasers., which coaniely changes the f eq.ueney of efle o botk iasers. Other types of tuning mechanisms exist, such as distributethBragg4efiector diode lasers with multiple electrodes. gradng$oaded external cavities, etc. .A. te ahertz transmitter incivde.s a trst photomixer that Is opdeally coupled to thu first and the second light. soUrce. A first radiative eietueMt or antenna is electricalLy: c.ouiicd to the first photon'ilxer. In operation the first antenna radiates a terahertz signal generated by the first photonuxer at.e dii r nee Ire upcy A teeeiver includes a second. antenna positoned to receive the sigttal front the target thdiated by the ifS antenna,. The second antenna generates a tone \ ai rng voiLgc piopo"tional to the tcrak'crz tetui n igi A second photonwkc I 15 cle.etdcaLiy couç led to the second antei.na and is optiauiiv.e.oupiied o the first and the second light source. The second photomixer generates a honiodyne downeonverted. current signal in respttise te the iJhne yaryitig vohag generated by the secoM apteorta. flie 4owncqnvefted. signal 1?3 a rncauierner1t of the Ethcorpti:on or retiectlon of the sample malerial at each tera:hertz ftequency This is useful, for example; when used in conjunction with computer procesiPg to reentlfy unkown samples by contpanng measurea tsuRs to a hhrar3 of reference spectra ths apparat3.s may ko be used to characterwe the freyency esponse eharacteristwc of passse or active components and devices such, as wavegiides, fllterc, athpiifiers, mixers dindei, and the like designed to work at ter&ttz frequencies.

SUMMARY OF TUE IN VENTION

L. Objes ofiho Invention [0006) It is an ohjeet of the present. invention to provide an improved frequency domain terahe:rtz spectrometer using, IWO contmuou&y trnahle semlcorid'uctcr lasers with the. ph. c.of the opdca. beam applind to th otice (IF dctection. photteobduite swItch hii eitctroni:càil modulated or adjustab1e [0007) Ii m another object of the present unenlion to provide a tcrahcrtz spewoneier fo the identi r.icauion of.a. target spectrum with high resolution and detection senshivity ÔE absorption bands of ihietest by producing CW radiation in one or more frequency bands, and "fine tuning" the terahertz radiation in. at least acme. of' those bands tq ldentify a spctra sigrature by phase mcbt.ion. :3

[0008j lit is also another object of the present invention to. mitigate the interlèrence effect:in. a frcque.fl:c.. dom,&n erahct speZtrome.tet jtb finely co'n'troth,Ne phase difiennce hetwen the n xing laser bean h v indically modulatng the ph&e 100091 II alSo &oihci ohj..ct of tnc prc'ern uncnUun to ehounak the,nift in mtrrft'rer'c c1 iti n e a icstut ut Wo%UTCOt uftht suun.t i decetui r]auve o the target I (P Ii is an oh1cct of thc preset rnvenoct ui provufr a method for niaependenfly adlUsting thc phas difference between. two source lasers forniing a eomposLte optical beam' used in a &eqttaicy domain terahertz ect.ronwr [0011'] It j another object of thO re.sent inhtiiti6n tO provide a method, fo* adjusting the phase.qf a ia.,er in a terahertz. spec.fomet.er using ph.otoconduotlve switches to previ.dv: more.

acdurattt. h.queney ap?cdcJty and resuhiUi'm by in*. .LU'fl1.n$' the teraberof. radiation. th a.

frequency battd O.f:hiterest. tuthg a phase modulator Mi"td a refeftnCe csciflator, j901 2] 11 is also anothu object of the peit i ivention K' ptovide a terahert spectrometer with djustahl esbIhti'On of'the thor of a MHz or 1U's of MH at spctifd fiepencv bands o absorption regions' cf interest by phase modulation, 0.i3i it Is another object of the rreent inventiot' tO ptovide a method for adjusting. thle phase of a laser hi. a terahertz. spectrometer using photo.condtctive switches to provide more aecurste frequency specificity and resolution by "tine tuning" the. terahertz radiation in a freqiency hand:01 mtei.est.

[0014] It is still another object of the iresent invention to provide a self<ontained, field portbic tc.rahertz speettonieter system in 8 couwact canfi.guratlQn eapable of idntiing or iniaihg an Object utilizing a 1&tser with an deetronically adjosuthle at controththie phase.

[0015] It is also 4nother ol:kjeet of the present invention to provide a tcriertz spcctronteter with adjustable resolution of the order of MEt or liD's of MElt at speci:Iic:&etU*tE1Cy bands or absorption regions of.interest.by adjustbg.1thestep or increment sIze Of the frequency swcep [0016] t is. also another object of the lrer.exit tnvention to provide a terahertz spectrometer v h adjustable Mgnal to noise ratio of toe order of 10 d[3-H, to 00 aB-Hz a: specific frequere bands. or bsorpd on xeion.s of interest by adjusting the. .tiiie constant nfthe lockin amçl.ilier.

[(101.7 it is also. another object of the prespi invention to provide.. terahert spectronieter with adjt.stahle tesoioUoh. of the order of Mu 0.s of MHz at sp.ectIc.ihqueney hands or absorption regions olintorest by adjusting, the nterferonc.o pattern.

[0018] ft is also another object of the. present invention to p.ro' ide: a terahertz seetrometer with adjustable resolution of the order of ME'iz. or 10's of MHZ. at specific frequency hand or atsorpt.ioo regions of interest by adiustin.e the titne period over which the sweep takes p1ce [0019] it is also. another object of the present nvennon to provide a terahert. spectorneler with adjustable: .r.nhtjon of the order of MHz or IWs of Ml fz Sat. snecific frequency hands or absoipuon regions of interest by pertorrnmg i phose sweep at a constan' frequerc [0020j. ft is also another object of the present invention to. provide a terahertz spectromcter w Ii adjustable resolution of toe order of Mil? or 10's ot Mflr at speutic treqLency hands o' aboEptioft. regions of intereät by adjusting the tesotuiion in the ftequncy sweep.

IIP.02 1] Some implementations may achieve fewer than all of the foregohigobjects.

2. Fatures of the invention [0.02: Briefly., and' In genil terms. the presenl discc:sar proyides an a.ppass for an&y7thg idernf)mg or imaging a target, mcludmg thst nd second hius havmg moable frequencies the first tase to produce a titst outp t beam and the second aser to procuce a wcar4 outpt. beam, the $rst o.tput beam and tic eecond output bear' hang chffere3 * optical equencics; a phase modulator positioned to receive a finn portion of the. thst output beam. to con.thillably modulate the phase' of the fiSt output beam and producing an modulated output third.bam.;a first optical elcm:ent:cmqte4 to the: mochUated cwtput third beam:and to. a portion of second beam to produce a. composite outntfourh. bean); a sonrcc:ot C'W signals in wrang of frequencies thm 1 00: Mi-k to over 2 Tl-Iz including a first photoconducEive switch activated by'ftw c'mposi:utptt fpunb beam; a radhWye element oou led to the sourc.pf CW signals for causing The CW signals to he a stantwlly sumd*aneow4y ocuccd on or through the target, second optical c'ement couplel to a portion of the first bean and to a portion of the seco id bean' to produce a composite output filth beam, and a detector fat acquiring spectral mformation from said target and coupled to the composite output fifth beam and generating, based on so.id spectral infOrmation and the composite output fIfth "beam, an electrical ign& reprcentativc of a chaiactertsflc of thc auct [0023] In' another aspect; the disclosure provides an apparatus 11w analyzing, ickmtifying or imagiog ai objet, including a' ourcr of (W,signal with an, adjustábk phase in, a range' of tiequencies greater than 1 00 MHz, d fte:cted to said object; and. a detector. for aci ring spectral ininiation reflected from or transa itted through said object and performing a heterodyne down POT. VCES$on fo.r generating an ekctrk& Signal teprs.entative of some characteristics of the abject.

[0C24 Ir arother aspect, the disclosure provides a method for aa4hzIng rdentTymg or in obect mcluthng genctatino. CW &gnas in a 1ange of frequencies tying above 100 MHz bti:lizing a phute modulator with it refinertoc osefliator and directing the CIW signals to said.

object, and acquiring spectral information teflected. titoni Or trattsnfitted. through said. object and peift.tming a..heterodyne:dow3i cnve.rsion. us.ipg a Iock4n:sign& from the. reference oscillator for geherating an ekctrk.al signal represtmtaUve oio.me characteristics otthc object.

[.0025] In another Lspect, the disclosure, provides a. method for analyzing, identifying or imaging a target by providing fi and, second lasers having lirsr and second output beams respectively haing different reouencies enodieafly uhae modulating the flrst output beam to produce a thlrd.beam; generating a CW'radiative beam using a first photoconductive sWitch in th range of frequencies griater than 100 MRrz front the first and thIrd beauts; cawing the CW tadiative teom to IDe subtan(iaI y simultatieousxv tocused on or through the target combining the first' beam and the. second beam into a composite fourth. beam; acquiring a spectral m.fO.U1-LLIOTI vga.l fron rud target using a scund photeconducu swteh 4ctlvated by said composite fourth beam; and.generadrqz: aP electrkal Signal representative 0f a characterisvk of said target using said specitht information. .ignal: and said composite fourth beam..

[0026 li' another aspect the Sacksuie rO\ ides a method rripusmg pmvidirg first and second lasers having tunable frequencies for prududing a first optical beam and a second optica' beam:rqspcctivciy with different frequencies; phae shflhiag or moth.iaUug the first o.ptc& beam to produce a finely adjustable phase sMiled thIrd aptcal beam. producing a conposite fourth beam.fhmi the second and the third optical beams; producing a composite fifth beam from the flst. and the secnn4 optical beams; criupdng the I nirth opdc&. beam to a first nhptoeepdl4ctive switch fur prodtu ng. CW raC thve beam tinge of ftequuies gedttn than I0 NIHL directing the CW radiative beam to be Ibeused onor through a target;. and detecting the radiative beam. reflected from or transmitS through the target by a second photoconductive switch coupled. tb the compt site fifth optical beam.; atd enerating an electrical signal fepresent4itive:of some characteristicof the tarabt.

[0027] In another pect Ia thscios.ure provides a nmd tbr teraherU. speciroscopr :inclodidg sweeping a source. of CW radlative beams cver a lange of frequencies greater than 100 MHz, including a first photoconductive switch activated by a first composite optical Easer beam; directing the radiative beam to be focused on.a target; and., acquiring spectra! Information from the target by a second photoconducuve switch coupled. to.a second eompobtc..optical beam; and adjusting the phase difference between the first cornoosite beam and the second composite optical beam by a.phase modu!atct in thpath of the first.ootie& beams used toge.iterate the first composite optical. beam, for generating. addi. tion.at. electrical signals representative of some characteristic ofthe target In a selectedfrequency band.

[O.028J in another aspect, the: disclosure provides a method. for terahertz speetmscopy including. s.weepn.ig,.hot in. frequency and in phase.,. a source of CW radiative beams in one or mere predetermined frequency bands Eying in tt range of frquenciea greater thai.i 100 MHz; acqumog spErotral w.tormanon. from the target;. and processing the spectral irifo.rm.ition to determine the presence of a specific spectral si:gnahire to identify a comporud of itterest i00»=91 The phase moddiator may bea lithium niob Ic modu1ator.

S

[00301 The phase modulation of the. CW signals by the phase modulator may resuit.in consttuctrve or destruefive interfernn cc oflhe:Tl-frhanj and the comrosi.tc outr.ut fifUi. beam on the detecthr.

[0031] A. signal source maybe coupkd to the phase modulator to aflow the.[irst owputbe:am to be swept in phaseover. 360 degrees.

[0fl32j rf he frequency of the signal source may be seiectahk toallow the operator to nayze a.specified frequency hand of interest..

:[C033) .Ehe signal.:ce coupled to the phase modulator may he swept in. phase tie ±hst output beam is swept in frequency..

[0034) hèterone detection ya#em may he provided that inchides a rock-in amplifier coupled to..the:dSctot, wherein the.sidal.OUrce eo0 jied. to the ph4se moduJgtor is also coupled to the lock-rn.arnp1i±ier :10035) The nurce OICWSignaIS may hteinde a tltst photooonduotlvø st1tch aetivated by the com.po.sttc output fourth beam.

[003.61 *fli first apd second lasers. may be disposed first. bouing; art.d the first photoeonductive switch may he disposed. n a second housing separate horn and. spaced apart from the. first housing wherein the first housing and the second housing are coupled by an optical fiber [0037J The first and second Sees may be disposed in a first housing, and the detector may he disposed itl athird housing separate Learn sM. .spaed apatt frcm the tltsthousing,:wher.eir& the first housing and the third housing arc coupled by art optical fiber.

[003] A povcr cource, key pid, nd diplay ma tic thspo,ed in the fipt housing [0039] A presser thay be disposed in th BrsthoUsing for dettmining a ciiaraetetstic of Uie target. based upon the abscrptioi characteristics of the.ta.rget in a frequency range in the.100 Mitin.cter2 THz frequency band.

f0U40J The cktettor ntay Include a second photoeonducdve switch nelivated by a second composac optical beau horn the first and seconc lasers that is offe in frequenc\ prom the first composite.opUenibeam.

[3041] itt first and eeond phetocortductwe sv itches tray bs. Iov temperature ron GaAs photocondutive switches, [0042] The first and e.copd.thErrnoeledtric coo1eri ma be coUpled to the flëst Uiid second lasers. respectively, for indecrdcnt1y coarsely tuning each of the lasers over:a.wawlength range of abQut S PI ir interyais.øt $tep sie of t 000Q1 ttt, [0043] The first and second lasers may be DEB or DBR lasers tuned to differert. freqtiendes.

(0044 the fIrst and second iasernnay b.c xterna1 cavity lasers,.

[0.0451 The.flrst opticlal. element may he..a wave.guide coupler.

[0046] The first phoiqconduaiye switch may he biased with, a constart electricai.potenti&.

[0047] The phase moduitor may be a lithium nibate. device.

[0048] be si.nal applitd to the phast. niod&4o may DC a penoWc o ki i sguel [0049f ibe ock-m acnphfiei may ho locked to the sgnal app1icd o the phsc modulatcu [0050] Tn another aspect, the disclosure provides *a method for analythtg, idwfli34g r inkzgmg a tage ompnsing geneuting CW beams m a ldngc ot ticqueneics lyu betcen 100 MHz tO vet. 2 THc sweepIng, both in.&ecueney dOd. in phase, the CW radiative beams. in Ohe or more predetermined frequency. bands; directing the radiative beams. tp the tt'ge arad acqomag spectral information reflected from or transmitted. through..thetarget [0051] The. CW dath'a.beaj.ftiS! beperiadically swe,ptin phase ovcr 360 degrees.

[0052] The acquisitkm of spcetra inth.rrnation may include use of a Teterodync detection syteth ilu ding a loek4n amplifier that is coupled. to the detector, and peribrm.ing. i lock-in of the detected signal to a signal appfledto the phase modulator.

[0053] A sigra sowce penodtcally SVCi in phast over 360 dogn.cs may he coupled to the look-in amplifier..

[p054] The.signal source periodically swe-t in phase over 360 degrees is swept at. a rate at least twicø as fast..as the trt4uoncy $weepihg rate of the laser.

[0055] The phase mod.Wdtion of the CW radiative beam by a phase modulator resuks in an i.uterftrence insensitlvity L.e. the deSted. signal is indepeadent al th clistante. between the acurce and the target. :1.

[00561 The phase modulation.o;f the CW radiative beam by a.phrse modulator results in the renioval of th uiterte:rence pttem.

[U057 in anuther aspect. the thsclostue provices a aiothod for araty'oig dentifyrng o imaghg a targec onpri.ing. generating CW signals in annge of frequencies lying between 1:00 M1Ek to over?. fHz and diiwing thopito tk target; and acquiring spectra! from or transmitted through said.obect. and performing a hetorodyne down conversion for geneaUng an etectnc& signal representatse of some diarateristcs of the target [0058] The firt apd seend iasOrZ may hy different tunable fr4çuencks, sd whercjn the frequency of at least one of the Lasers is swept or tuned over a frequency range. of at least ROIl GEL with asteg sizea.17 a ew&2 GHrso as to produce a swep.t UW radiative hewn n a range of frequencies lyifig between 100 MHz. t thëi 2 1Hz.. dli ted to the target, and th.ha p the laser is swept.ai a rate at least twice:as thst as thetequency sweeping rate.

0059] In another aspe$ the d closure prosde a method tor terabertz spectrocop ui tiding sweeping, in freqt ciii" over a selenabe treque'c) range, 4 soon e of CW radiative beams in one' or mere predetermined frequency bands lying itt a range of frequencies greaterthan MHz, acqu'nng spectial information from the taiget a'd process ng the speetiaL i iforiianon to determine the preset cc of a pccific spectral signoture to Locntlfy s compound of interest [0060] In another aspect, the disclosure provides a method fer eraheriz.apectrp$cvpy including sweepin& in a..seledtahle et off equencies. a soIrcë of C\V tadi.atlive beams in one or more predetermined frequency bands lying in a range of frequencies greater than 100 MHZ; acquing spectral mfornation from the Large and processing the spectra mferr'ation to determine the piesence ofa specific speetnJ c?rature to dcnnfy a compouwl of riterest 12.

[00611 in another aspect, the disclosure provides.a method for terahertz speotroscopy inc udnig sweep ng ir a frequency hand ith a seIectahe step o' increment size, i' source of C\S iadutw& beams in one or inure predeteiminen trequei:y bands tytng in i range of frequet eics grether than 100 MHz; &qu. ring spectral ihformation from the target; and processing:thespectral thfbrmation to detetthihe the presence ala speciic spettai signature te.idnti1i a conipound of interest.

[00] in. another aspect the 4isciostrre providq a method for tcrahertz SPeCtrO.SCQr.Y including swCeping, h froqaenej..o.vcr: a adileetahie time peiiod, a source ofGW radiative bruns in one or more predetermined frequency bands lying in a range of frequencies greater than.100 Mhz; acquiring.spectr1 infbrmation rpm:the target;. and processing the..spectrai inf rination: to detennine:the.prateo ala speeftie pectrai:dgnature to ktentifya compound, of interest [00631 In another aspect, the disdosure pr.osdds a method fir terahettz.spectroscopy i.n.eiuditig sweeping. i'T e.. frequency land with, a setectabip resolution, a source ol CW raditLve beams re one or more predeterm ied frequency banu l ing in a iange of freoucaucs griatci than MHz; ac.quirihg'speetral information.'from the target; and processing the spectral informaiion to determne the. presence Io:f a \pecif e spectral signattite to identi.fi a compound of' intresL [0064] 1 another aspect., the. disclosure pmvide.s ti method for teraheitz spectroscopy nclud ng sweeping source of I W radiative beams 19 OflC at more pred termmed UCUe1IL bands ying. in a rangt of frequencies greater' mu Mkz acquiring spectral inth.rinatlon. fron.i the' target; and processing the spectral information iLh a lock-In.. arnpuifidr with an adjustdbk time constant to.dctenrdne th. presence of a specific spectral signature to idthtify a comp'ound of interest, j:3 [0065] In another aspect, the disclosure provides a method tbr terahertz spectroscopy includin.g sweeping 5 scyerc4 of CIW.r.thtatv beams in one or. Piore jtedetennined freqttency bands lying, in a ranp of frequencies.grcatr than 00 MI fri; ecqtiitiitg pectrai wherein itiformtion fro the target; and processingthe specttai:thfhrmation with means for adjusting the Int&ference paueth to dé.terthine the presence of spedtic *ett1al igp4We to identit compound of interest.

10066 In the sweepi ig process the step szc may be selected by the se to a selected value is an ennipie, in sonic.em.hndinnts tn:a valua.hetwccn.100 IMHz:th 5 GHZ.

[0067] In the weepiflg process, flit number of frequencies may be seketed by theuser a :se!eetedvalue,as an example; hi some: embodimentsjc 5 between 100 and.2000.

[0068 n the sweeping process, the tin e peilod of the sweep ma be sdertd by the wcr Lu 4 selected value, as an example, in smije embodiments, tO a value between 10 seconds and 1000 ecoridS [00691 in the sweeping process, thestep siz; the juthber of frequeacie.s, and the tin eperiod of the swep, maybe adjustt4 to achieves given resolution and signai to no.iseratio.

[00701 Some implementalions or embodirn ots may neo.rporatc o:iftplenjent fewer of the aspects. or featuresnofedin the foregoing summaries.

[00711 Additional ohjct, adVantages, and ovel fiatures. of the present invePtion Will become apparent to those sk lieu in the art from. this disclosure, including the toflowing detailed description as well, as by practice qf.bc invenhiQn. While the inventit is dès.cdbed.bnlow with.

reference j preferred embodiments, it Should be understood that thC invention IS not [limited thereto. Those f o:rtRnary skifi in the art having access to the teachings herein, will recognie additiona.l applications modi.flcaticrns and embodiments 1±1. other.fteid, whkh are within the scope of the Invention as dielosed and claimed herein and with repeot1 to Which the iirVefltibn could be of utility.

BRIEF DESCRIPTION OF THtDRA WINGS

[00721. These n4 other fetitures and advanages of this invention wIfl be bctter tmderstood and ntOre ftdI 4precitited by reference to t.hetbllowing. detailed descrIption when consi ered. in conjunction with the accompanying drawings wherein: (0073] FIG IA i a bkck. diagram of 5 frequency domain terahertz sbectrometer øccording tothe present disclosure which employs.reflection from the sample; (00741 FiGs lB is a block diagram qf a fteqqepcy darwin teraherrz spectrometer accordth,g to the pesrnt disOihn:re *hich Cniploys tranñiissioti from the ariiple; (0015 rrc;. 2 is a block diagram of a frequency domaid. ter&iertz spedrometer of the prosnrdisclosw'e; and [00761 PlC 31s a block diagram of:a hctcrodync detection system. subassembly.

[(077] The novel featcten. and characteristi cs of the disclosure are set. forth in the:43p0t1d claims,

LET4ILED DESCRIPTION OF THE.PREFERE1J. MI3ODI.MENT

10078] DeEa.iI. of the present. diseiuure will now he described, including eNempiary aspects atid &mbodhntots theteof RefefflrLg to the dtawid.g and the MiPsViit ducription, like reference numbers are used to idcntfyUke. or.functionallv similar elements, and.are intended to 0 qstr4te major features oiexeniplary emhuI ments in a.highi' shnptifl.d. .dingrairmnaic manner, Mthcover the dthwings are not intended to depict.ecery feature of actual embodiments or the relative dimensions of the4epicted l.emeiits and are no draoi. to scale.

[0072] Reference throughout this spedtieatibon "one enbdin nt" at kan emhirttt' means that a particular feature. structure, cr characteristic, described in connection with the embodiment is included j at least one enibodiment of the present invention. fhus the apparahces. of the phrases cj:flg embodinient' Or in an embodiment" in Varioq places throughout this speCification are nOt necesatiiy SI referring, to the same embodiment Ftnhermore, the particular, features, Structures, or characteristics. irlay he eombned fti any suitable macmerlin one.or mote emhodiments.

[0080] As noted above. in the frequency domain technique fbr terahertz.spetroscopy, CW ti-fr radiation is produced through phtnmixing of the: combined output of two.sngio-frequencv diode asers ni a low tcn'perature gioun GaAs photom"cer or PC S the wavekngth of one (as both) of the lasers j5: tuned by temperature adjui,tmen of the laser to coarsely vary the I}Iz output frequency shch may therefore b swupt over one or more fruquem> bands of ulurcst for IcharaCierizing the tatgdt or npk matc-riai.

[00.1] In most frequency domain.spectro.meterr. c'oherent (hornet yn) detection can' he a.e.hievd t room temperature by thi'citig the SatuC. opttcai. radiation.&oiii the diode lasers. in a :dethetot PCS onto: which the rcflirn THz signal is also incident. This. prcvide similar or greater sensitivity and faster data acqUisition than the ncoherent: techniqUe.

ltxTh'21 in a terahettz spectrometer, the ic ahe z radiation is focused or directed to the target sample to be arudyze& and a detecuw:01 detector array is arranged to collect the signal pro$gated thrtiugh or.teTheLt-Sd.fron that tatge.1. tWy triodes of fran:sm.iscior or refleetioi.i from the target are iiltistratqd in FiG, IA and ill.. The configuration or arrangement.of FIG. IA dep:icts. refle kin, land Ft:G: lB. depicts transmission. thrnuh. th target ir SMPIC by appropriat placement of the soutcC head ot module:201 and th.e.detector head. or ttrOdok 202. A housing:100 (shown i IG 2) meocporates the use" mtertsce and the optiea and &cctroopucal components associated h the coupled apctrcnneterhad.s of FIG. A and tWin one embodiment of the 1resent diaclosute, the tnoduics 201 and 202. arc enclosed in diffctcnt. hcusings, each of Which may he ma iu$h mosed 0! posuiunect by the opeatoi wfl.h respect to the sarpk under test & fiber dptit àbie 117 and an electriCal cable 212 couple the hOusing 100 t the.it&Lde.201L ani Then optIc. cable 118 and an electrical. cable 215 couple the housing 100th the module. 202. The silicon lens 205 on the.. ..ext:erir of the housing.201 enables the terahertz radjaflon to be focused or óirected told tatget by the uet, and the silicoh lens 208 oh the dxtetior of the hoUsihg 202 is positioned by th user sq that it. coflects the radi tionrnsmit d or r cci rom the target; It. is noted: that additional optical elements including hut not linflied Lu lenses, EbcusIng: mirrors parabOlic reflectors, sub-reflectors, bearnsphtters/coiriblnets, and beath--.haping optics (not shown for clarity) may also be employed to provide focusing or manipulation of the radiated terahert:. beams, as the particular mesutethent situatiot, requires.

[00831 FIG. 18 is a block diagram of a representative spectrometer arranged 1oentilo transmission: through the sarnple The operation of the varjcius components are substantially identical to the operation in FIG. IA,. and need. nut he repeated her* The figure illustrates how the ouree and deluctot housings 20 and.202 may be manu&y moved and pos4tion.ed hy the operator with respect to the tar.et. Alternatively; the soureC and detector hotwmgs 201 and 202 may be combined into one eomnwn hmsing [00E41 Turning to Ff0. 2,: there is depicted a housing 100 mcorporatmg the optica.l and eieetrcoptica1 components suited fbr use as a subassembly in conjunction with the coupled spectrometer heads of IG. IA and 1W In sonic. .embodimenis, the housing: is sized and dSgned to. he lighuveight and portahk, and worn or supported by the ir during operation.

Lascr.subnssemblies 10 and 102 include lasers: 105 and 106, respective, which are preferthiy tv,o 78 nm distnbuted feedback (l)}'B) or dstnbutcd Bragg reflector (DEE) emiconducwr laser diodes w di sing e4onitudinat-mode:and. single spatial-mode opernuon over the. desired range. of wavelengths,. available. 1mm various. vcndcrs (for cxamØc, Eagicyard. Photcoics. (injbf]I cf BCr.ljn, Gertthuiy, or PhOtodigth, 1nc. of Riehard1somTexa). lit some embodiments it would also be possible to utdb..e one or.ore packaged ektetnalcavity tunable emieonducto iastN such as are.availabie from Emeore Corporation, ot Newark; .Caljfijniia such as disciosed 4 US.

PatenLApplication Setlal No. I7Z2.gt5 tied Mtwóh 12, 20.10. in one ethhodjment. the output of' one laser is adjusted to 78 nut, and the output of the other laser is acflusted to 784 rim. The diode laser packaging p.enpi.ts co"cofl.in.mtion of the laser beams to a very high degree of 1recisiofl, and the design allows vet.y:Prise ftequeney ohtro] Of the.iaser4 by temhtrdturC and/or electronic turüng, and monitoring the laser output through digital signal processing, to achieve:mre accurate control over thejaser.output.hesm frequencies.

[00851 in. one embodiment, the flaer diode chips 195 and 106. mouhted on independeht Peitier iherrnueiectdc coolers. (TEQ) 103 and 104 iiie center wav&engths oP the lasers are nominalit 783 riTual 25°C, hut the wavelengths may he coarsely temperaturo1uned with a tuning coethceni.&: apprhxitntet ft.i nm per °C. Therefore. a 50 degree.C temperature, range of operation from $0 degrees C to 44} d'grees C will yield a frequency range of apjiroidthately S rim. For' the purposes of illustration only, lithe' 1MB lasers are selected such that their center wavelengths at 25 degrees C arC at 782 ntn.snd 784 not resneethely, then a thermal tunjn.g range of ul.0 degrees.C to +40 degrees C on each laser chip will permit. generation of offset wavelengths C urn to appmxim.ately 7 urn, corresponding to a range of offset frequencies from 0 E-I'z tO 3.4 THz, The theimal mass on the cOnti'Oiled surface: of the ThC'** iS udi that it alloys rapid frequency tuning. [ the ease of DBR laser:d'i&e chips,. the. Brag.greflection:secticn of each laser may he:adj:'u'stc.d ieetrnniciIly to vary.the: laser frequency. Wider offset frequtncy ranges tha. also be pohibl,'by tioloying widei ththper4ure excut5i,on: us.ib.g [>13k or exlerta1eavily lasers.

[Q186] Ih.e.o40v1 beam. from oath laser 105, 106 is collimated with an. aspherie lens 120, 121 respeetre1, n'ounted on a ret sg'n kremount with uh mtcror adpictment eaph'ky ccc, e,g. tLS. Patent 7i 2.6,078>. \ft.er passing through the. lens, the laser output beams are directed through,a rep0ttivC eptitht isolator 122 and 123. to pryent [edbapk into the. inset, atø to couple the output beam to pigtail optical flbers 107 and 108, respectively.

[008/] A 50 50 iavegnde cou+ler or heamsphtter 11Sf and B82 are coupled to P-ic pigtail opuL<il Ohrs I 0' and 108 rccpectrvt I, and the outpu huams on Iiber\ 107 and 108 are cat h pft into compc.site primary and secondary beams 10.9 and 110, and 1111 and 11.2 respectiveiy [0088] En the.em'bodiinen't'denibted.in the prese.ntdi.s.dosur.e, the primary output beam I 09 i.s directed. along a..nber or first path to a phase.cootrc.t element such as a phase modulator 11.3. The: phase modulator 113 may be an lithium niohate device, such as those manufactured by Phothne Technoioti.us ofBeancon, France Tho pb.as odUlazor ii 3 al ows. the user to wep the phase automati:caliy (by preproray1nnvt sofiwaru) or manually ad3ust the phase of the S& output beam. I 09 in a highly precise. manner, thereby So adjusting tie phase of the emitted CW tørahertz bean. The out ut ot the phase modulator ti is then coupled to a wavguide.cOupiet oP beamuombiner HO. ha some embodiments, the signal applied, to the phase modulator is.a.

pe"iodic 6 kHz signal or mare generally, a pertoà signal that is swept at a tate at least t4ice as fbst as th rate at which the luser frequency Ia. awept.

[0089: A tunable reference oscillator 114 is. connected to the phase.rnodtdator 1 13 for swiepn.g or precisely hmretnenting or deoretneniing the phase. by e p.eri.odIie or other tyne cf signal.

[0090] The beam HO is directed along a fiber or first path to a i. avegu.ide coupler or :he4mcombiner BCZ nd similarly the beam 112 i dllrected. aloPg a fiber or. first p@h to the wave.guide co.uiet ut' beameombinur BC, Thu output beam. from besnsp1iue BS2 Ia directed aiong:.a flher 118 or first path so as to exit. the module 100 and is subseeuently directed by ber ifS to the detector beid. 202..

[Q091.] Thc output bean. lii. from hearnp.lFt;er DS2 is d.wected rdong a. fiier r first path to the beanicotrduii,ner lit!. The output of the phase modulator 113. is directed along fiber 116 to jti beanicom.biner. BCi. The output of beameombitier BCZ is then applied to fiber 117 which exits the module 100 and s subsequently directed to the source heao 201 [0092.] The uptic4l ptopalgation. path donstream of the laera and througheut the unit 109 may be an appropriate singlemode po.ianiz.ationrnaintai.ning optical fiber PMF) or free space. 20.

In the case ot opt cal 9ber constrt enon, the beamsLtters ma' be replaced nq su4tihle opticai wavegaide coupier. As can he. gppreciate4 the basic tMpology depieled Th: FV.2 uses fibor opocal implementation which readihr iflastrates the various optictl paths while FIt 4 will iilnstratc.a freo space implementation.

[ØQ93]. The, bam tIom bc:aincombir*er. IKI is. coupled to a fiber 1 f7wh kTh is.ilen.c.otpie.d the external source head 201, as described above.. In source head 201.,. the composde output beam of the. two distinct laser sources is then applied to a lens 203 fich focuses the beam to a spot of appru?irn4ely ten microns in diani-ecr cm the surface of a low temperature grown (LTG) gallium arsenide (GaAs) photocond.ucthe switch (PCS) 04 The two optical beams. are combined or photomixed. in the PUS 204.. Other types of photoconductive switches may be used as well. The las&beam n-lay. ft)cused at a gap in anthnna.circui.tp:attamcd on the suriàcc of the. ICS, xhkh in some embodiments is in.p.kmented as the Sf}tF& as shoWfl..n FIG, .2, with the gap located at the center of the spiral. A constant..DC tkc-trital bias coupled toThe source head b cable 217 ma also cc pplicd across the term nas of the antenna or dir PCS in some embodiments, a. known in the ptior arc, a slowly timer-varying (i.e.,, ith0pptd>): electrical bias signal may be applied across the terminals of the antennacn the PCS..

[11094] The terahertz variation hi the intensity of the mixing or difference signal betwee.r.. the two laser frequencies, often referred to as the "heterodyne laser sigudi", produces a tdrahertz modulation of the e luctace in the. Pç.s material, which in to. produces.a:tctahurti cuueiu f.(w in the.attenna patterned.on.the surfaof the PUS.. This current in theanteima produces an eiectronia.gndic field, he. terahertz radiation, propagating into the surrounding space and having a frequency range front typIcally 100 MHz *b.over 2 1Hz, denendin. on the difference freqitency of the tvo laser sources. The tetuherh.. radiation so prodUced IS t -Itted frum. PC.S device 204 and theti collim ed and coflected by a silicon tens 205,. preferably a hemispherioaIl shaped structure. approimatey two to three centimeters th. diameter. .AdditicnalI lenses (not. bown., con, posed of'TEFLONTM or other suitable.rnatedal; may be placed downstream of the kms 20S to. Coilj.tC the RF beams into an output teraflertz beam; Beam-shaping. mirrors may also be used in lieu, of or in additidti to the i1idorr ins 205 hi the sourCe head 201.

[OO95 The outgoing terahertz radiation beam from currently available PC S devices is relatively ow power, about I to 10 mierwaits The. rget sample (not sbQwn} is typilcatly positioned' relatively close to the \ç)tIrce ni.d cieectot heads, and. WIt! absorb nod ttanstrlit srn terahertz radiatiom and. also retkct. a portion of the terahertzradiation back iii the direction of the source or tiser, as shown by the return THz.hear. . tFlG1A [00%] (hi the receiver side of the speetrométbr, the beam from beathoonthiner 110 is coupled th a fiber 11 g whIch is' then coopted to the external detector head 202 as described above., In deteewi head 2:02, the. cotnpesitcoutput beam of th two. dhtinct laser soutcçs. is lb. applied to a tens 206 which foci.ses the beam to a spot of approximately teP thictons.diaiDe:1 on the st rface of a lo temperature grown (1 1 G gailiur' arsanide (GaAs) photoconductivt switch.(PCS) 207 The two optical beams are combined. ox pbotomixe.d in the ivc:s 207. Other types of photoco ductrve sv tcnes may hc used as wall The laser beam ma be focused at a ga in an antenna circuit nattenled on the surface of the PCS 207. whIch in some. embodIments is implemented as.the spiral as shown in F [0... 2.., with. the gap located, at. the.. center of the spiral.. In.

some embodiments the spiral antenna on the. dotector'PCS.207 is implemented in a clockwise direction, in contrast, to the: ceunterctockwis'e: direction of the spiral:Sntetlna on the soot e 204.

[0097] The terahe.rtz return signal from: the sample or target IS captured by a suitably positioned second silicon lens 08 in the detector head 2G2., whkh focuses the return terajierta bCarn to theantenr1a On. the surface of PC'S 207 which acts as a terahertz radiation deteotcr.

[.OO8I lo the prior art:cmbodimcnta, the tcra1rcriz variation in the intenity of the nthcingor di.ftrence signal between the: two laser frequeneies. in. ooitibinai.ion with the terahertz modulation of the coaduotance in the PC'S naterial,as A result of the terahertz.currcnttlow hi the antenna: n the i.eceiyed. terSrtz. signal torn. the sample, reuJt jn a: hotrodynç down coi.wersion. *17 the tecelved terahertz signal a> a basehand frequency equal the: ctiopping' frequency that may then be detected byn synchronous citcuit such as a "Jocldif' aniphfier:, or sirn las anangctneifl.

00991 in embodiments contemplated by the presect disclosure the teral'er? anation it the intensity of the mixing or difference signal between the two laser frequencies, in combination wwi the tcrihe t moduaition of the curicluctercc in the PC'S watcjia as a. resu + of nc current flow in the anienna ifrorn the received terahenz signal from the sample, results hi a heterodyning and. down conversion, of the received terabertz signal a baseband frequency equal to the frequency of the reference oscillator 11 4 Tue synchronous deteetion circuit makes use of the:reference oscillator 114 signal applied to the phase niodulatot 113, and thereby signal applied, to source PC'S 2t4. as a reference for the syndbronous detection process.

[00 lOG] A signal resalting fiom this heterocyne dctcetio stern 209 may he coupled to and processed by processor 210 The spectrometer may further incorporate software fOr automatIcally determining the identity or c,cmpps.ition of the target, and other electronic element for printing or displayhig the.resuhs so that the analysis, kkntiflcation, o.r.hnage information is 2) readily availahk te. the user.;. FlG 2 illustrates.a communications interface which may be a wireless. RE transceiver for co:rrtmunicatiag the results to an. external user. ør network element) 211, a disp1y 212,. and a keypad 214 as eiathØ[es of ekthents j.roviditig User Ot operator interfaxe. .A battery 21 3, or other selfcentained power source, may be provided to make the unit

fiei.4 portable.

[00.1011 ifl one embodImetit the frequency of one of the lasers, and cOnsequentially the radiative terahetir frequrmcv, is swept or iunedt rough a series of frequcuei.es. or through a sequence. of distinctspecitik> frequency bandS. The returh tenthertz sigmil S, is.collected h' the detector and transferred to processor 210 for data collection and analys:M at each specific frequettcy of interest in this: way,. the absorption ortetlection sp.ecfrum of thø sp1eundei. Lest.

can he collected. with h.ih. resolution and high s gnai.tonoi1at ratio since all.of the terahertz energy is centered in a siegie tone and ifie lock4n amplifier limits the flOSC: bandwidth. This, incidentálly,ts a major advantage of the frequency domain tethrtique compared to time-domain.

techmq rca n aucn ftc teh*ertz ererg s spreac oter many frequenue\ In sonw eivnoumwnt, the tuning mid terahertz: emission. may he adapted t.o a specific sequence or set. of frequency hhds having specttal aiSorrhO.p pedEs: orre$,fld,irg to the Lmique spectral sigitatur of a particular material of concern. Thus. the frequency sweeping time may be minimized if the user's ap itcaticu was solely the question:. "Is.compoigd;X present in the sampIe?" since, the processor and sottware w the spectrc rieter may 1e prep'ograrnmed to ons generate seep record and analyze the tetanertz frequency banls ascothated wth the spectral signature ol a pcticular mater al olconcern 1001021 FIG 3 s.n enlarged bled' hegram of a heterodyne detection system subassembly 20$ .showxj ju FIG. 2. The reference oscillator H 4 provides a reference signal that. may be adjusted by the operator between 0 and 10 0Hz in selectable step sizes or intervals: ra.nghlg from 1 E±t.o 1. t]flz. The sigPal..ftom the d$ector PC is applied onlIne: 21.5 to a low noise atupifier (LNA} 301, and then to a synchronous detection circuit 302. The downconvthed output of The synchronous det&tiott circuit.02 is then thrwar&d to the processor 211, [00103] In suimnaty cett.aih aspects af The present dSiosuft niiy provkle a. compact frequency domain terahertz coherent spectrom.ter with either continuous tunhig, or discrete uning within cerizin identified. tltqueiey bands greater than 1 (iC 6Hz. S'4ch co.nstrucliqn may employ hIghly contpaet phoionic i.ntegrathn techniques nnd roomaornperacure coherent THz detection, Advantageously, such devices may offir rapid identificatien of chemical, bidlogiddI and explosIve nsterials n both the. solid-phase and the gasnhase at standard atmospheric preSsute. Sonic enihodirnehis tidy tUthze a. highly integrated.photonk. tssttnb.ly employhig enieonductor diode lasers employing no. moving, parts., so that it is inherently rugged and welk su tea to hed deployable applications The trequerey shthec optical beams are incideat on the source P08 (or aitethativeIy in other ethbodirnehts, the detector PCS. or both), and. provides a.

ineau to eftec exhemel) hig'i.iusoLttion spectiosuip' I yçtcal theimal iumng iesolution and accuracy of the source asers may petform coarse tunine oet a %saveiength range up to 7 nm, m nurvals or step ies of smaller man COO mn lOU 104.].: Of course. varipus niodilleations and item of the present dfseiosttre tay ahs. he. apparent. hi those. ol ordmwy sidl.l imthe art, Thus, the particrd.ar combination of patts ddscribed and illusi.rated herein is intended to represent nub' certain eniboditnents of the present inventhn, and is not 1. ended to serve as. iimitation of alternate deviecs within the spirit and scope of the inventIor, IOO 05] U wi]J be undtobd that ac.h of the eLants described above. or two or more togethe.r. nlso may find, a. useful aipikation in. other: types of ccsnsttucUons differing, from the.

types described atove, In particular, certain configorations presented aceotding to Mrticult aspeCts of the' resent invention have been shown and described as discrete elements. Le, iaser, splitters, .conibiners mirtOrs, ldn.Eis, shifters, fiber optical cable, etc.. Thc&skilied i.o:the.ati Will.

readily appteeiate. that many or all of thce indiyidui. discrete.coniponSts may he fabricated an:d/or packaged into integrated' elements By way of: particpiar example, lb. use 0! wiegrated waveguides and associated structures i cmi skrie4 for the. described truetUres and arrangements. .:iternati.yely, the discrete elements, i.e., iasers splitters, combiners., mirrors, lenses, shiheis etc may also be mdividuaily packagea in moJule w4h opLcal fiber interconnects to achieve the same topology and fUndtotiälity [0UI05] While the. piesent disclosure illustrates, and describes a tcrahertz transceiver or spectrornetef y5tetn, it.a, riot intended to ht lithited. the details shown, since various mqdifica.ttpns and tructural changes. may be made withota departing in any way from the spirit.

of the pres.nt. invention.

100101] Rcercnce throughout this sne A non in out ewbodirnent" or an cmbodm eat means dat a pani.cular feature, structure, or characteristic described in connection with thefl emhodirnerit,is. included in: at least One embodiment of the present inveniien. Thus:, tr!e appearances of the. phrase's in one embothmentY or "in an embodimenV in. various places throuehout this spec'ticati'on are: nut. neceasa'rih all referring to die same embodiment, the. partcuiar features, structw'es, or characteristics. may be combined in any suitable maimer in one or'.rnore embodiments.

[00108] the foregoing described embodiments depictdifferent components comained within, or cohuected with., diftèrnt..th.er cOmponents.. ft is to be understood that audi depicted arrangementS or arthitcotures are merely esstnplary, ajidthat in fact many other aiththgeinents or architectures can be. implemented which achieve the same thncticnahtv. In a conceptual sense, any iThngtheht of c:omppfleiitS to achiove the same functionality is effetiyeiy ssocited" such that.the.dsired functionality is achieved. Hence, any two components hereib con. timed to achIeve: a particular functionality Can be.: seen as assocdatdd with' each. other such that the desired functionality iS achi'Cd, irrSptcth'e of specific svruturOa, .arehitetUres or interjne4iai.

componen.ts Likewis; any two components so associated can also be viewed as being "operably cormectéd" or "dperabiycoiqIied" to each ether io:aebi..vc the desired Iductionality..

j00109] Whiie particuhit embodiments of the. present:thy.oitkm base been shown.. and described, it will be understood hythose skilled In the an.. that, based upon the: teachings herein.

changes and modifications may be made without departing from. this mv ition and its broader aspects and, thcrethrc the appended claim are to rcompacs wtbrn then,cope a'l sud' chngec nd modthaaons as are stthrn thc nue spirit and scopc of Ui s on cotion m urthonnoic, it is o be understoo.d that the ttwendøn i solely defined by the appendiad elain: It wi he tSrstood by thost wnnn the art that ir genera tcrtis used herein and especalis in the appendeo chums bodte of the eppendtd danns) ate genetaHy intended as opeit" teuns Ke g the tincludirmn thouid be inttpteted aS "mnc:ludln:g but tat. limited tOa" the ter.th "havutig" Should. he irterpreted as. "having at. least;" the term "ihcftides" should he interpreted as "includes but is not hruted to " "cnrpse" and sanatwns thereo such as. "compr ses" and "compnsri.g" are to be ennatrued. in an. open, inclusive sense, that is as "including, but not limited to ete).. It will be further understood by those within the that li a specific number of an introduced claim r&oitation is intekd, such an intent will he explicitly recited in the claim, and in the absence of sod, recitatidn..no such intent is j*esent. For example, as an aid to. understanding,. the Riflowftig appended daun may contain usagc of the intrcducton phrases "il least one l sac "onc Oi nlnr& to nitroduce chum recitations I fowever, the use of sad phrases should not tic construed to mply that the introductiOh of a clain ieitation by the ihdefinite altiCies "a" Or "$1," limits any pa:ic4r claim containing: such introduced claim, recitation to. .invehtions containing only one sudh tecitation, even when the same e]a.in-i includes thc:intouctory phrases "one or more" or "at least one and ndefThite atticles such:as ta" Or "atf" a" andkr "Øn" hoqld typfcafl.y be inrpeted to mean "at least.on&' or "one or more"); the same holds true for the use of definite.

arucles used to u',tleduLe chum reutauons hi add non e've i if a spcuf on nber of n introduced o[itim.tecithion expiioitl recited, these skilled, in the art wifi tcOgnizc that such recitation should typjçaily be interpreted to mean: at least the recited number (e.g, the hare recitation. of "two recitations," ythout other.modifi ra,. typ?Jly means at least two rec1tatior5.

or two Or recitations), OQ1 ii)] Without further a:na1ysis: from the foregoing. others can, by. app'ying current.

knowledge, readily adap tile disclosed technouog for arious applications SLch adaptations should and a e m'en&ct in be (omp'ehended w1thin the me'umng and rane of eqi iw ence ct the following claims.

Claims (6)

1. Whatis claimed k: I.. Amethod for analyzing, identifying or ntaging a target, othprishig generating CW sigSs in a. range of frequencies I1ing between 100 GH± to over 2 17Hz and ci ireetin them to the tar.t: and acquiring spectral information reflected from. or transmitted through said obj.edt and perforn.thtg a heterodyne d.owncotweathn for.gcneratpg.an eect.ricaJ signal rcpresentatiye. f some ehatatteritics of the target.
2. 2. A pietbod.as:detined hi claim I, .tuftht eomprisiflg proyidThg. .1 rst and scoud lasers having different tunsbe *equencies, add itherdin generating CW ignais includes acthti.ng a first photoeonductivc witJi by a fltst cc11peite ept al beam from: the first. awl second 1aser; and varying: the phase of the first composite. optieal beam.
3. 3. A mpt od aS efthed a ca 2 further comprising providing first and second lasers having different tunable frequencies. and wher&n the.freqwncy of at least end O:fthe lasers i. Swept Or tuned over a frequency range of at least GIlz with a si.ep sue of a. least 1.00 MI-li produce. swept CW padiative beam lb a range of freqcncies lyibg between 1 00.Mft to over 2 11Hz directed to the target. and.the phase of the laser is swept at a rate at. least twice as fast as the fecuency segphig rate.
4. 4 A method as defined in ciahr. 3, wherein the heterodyne doimconversion includes acu'vaUnga second. photeconductive.switch by a spcon.d composite oica beam from the first and second lasera thu is of sctitt frequency from the first ojni di beam.
5. A method for anazuig dernifyirrg)fl nnug. Urgct comprismg genctatthg a fitst composite laser beam comprising a first laser beam at.a flrs.t frequency and a second laser boaw. at a second frequency; generating a CW radiadve beam in the nnge of trcquencws from 100 0Hz t..o ycr 21Hz from the firsteomposite taser beam using a first photocondncrive switch; causing the.CWradiative bean, to. be. substantially simultaneouslyTocused oi or through the tafgdt; generating a second co.npos te. iaser beam. comprising the first laser beam and the second laser bean, acquiring Et speWa] inftwnjatielt$igfll fro said ttcget utg. a secone photoconduetive switch activated by the second: composite laser beam; $wcepui.gthc. frequency ofthe.CW radiative ben over a selected range of frequencies by varying the difference between the first irequncy and the second. frequency; and generating an electrical signal re.preser.itadve of a characte.ritie of said target using the.spectral,nlormuon srgnal atqu rea during the sweepmg of the C' radwtivc beam o er the selected range of frequencies;.wherein the. spectral information signal comprises, a component corresponding to: mcduiation. at a modu:atton frequency; and the electrical signal representativeof a characteristic.of said target.is generated by a iock..in asnplifieratthe modulation frequency.
6. 6. A method. according to eiaim 5, wherein the frequency fthe.CW radiative beam is sele table to allow the oØettor to wlyOa. specified frequency hand of ntcrest / kmetticd ccordrngvi c aimS ot 6, wherein said modulat on ts phase trodulanon A method according to any oieluir.ns 5to 7, wherein the. lock4n amplifierlis arranged to.temoc'a an intarfex:encc rsattetn..9. *A tcrchertz speclrometer comprisitig flltid and seeo.i:d lasers..navjng tunabLe frequencies said first.aset to prqthcc a first outpu.t beam: anti s&d second lasenop.redice asecond cwtp.th: hewn, said tics output beam and said second output beam having different frequencies; a moduLator pc sitioned to receive a first portion of said 11r4 output beam to eonttoUably modulate the phase oldie first output beas.nand producmg a mOduhfled output third bcarn; a fin;Loin1oa teniept coupled. to the modulated output third beam arid..to'a portion of th aecond beam to produce' a composite output ft urth beam; a souive including a firtphotoco.nductive switch aetiyateci by. the composite output fourth beani to toduce CW s.gnais iii a, range of fttquencic Itom 100 G}i. to ovçr 21Hz in d.epentene on the.freqency diffetcflce Of the first and second ournu1 beams a rridiathi'e eknietit coupltd to the sOutte of tW signals fit causing the CW signals to be suhstarthaliy irnultaneousiy:ocused 011 01 through the target, a. second optical eiemehteotqled to a portion oithc first b:nm and to a portion of the second beam to produce a coMposite Output fiftb.beam; a detector for acquidng pec.tral information from said target and. coupled j the composite output 11Th beam, and generating,, based on said. spectral. information. and the cartpositc output: filth beam, elec&i.cal sign& representative of a charpeteriMie ot':the target.; and a tockjn ainpiifierfo.r detecting a component in the electrical iigmd correnondinq to modulation introduced by a signal source, 3 J 10. Alerahertz spectrometer: wcordingto claim 9, wherein the signal source is operahleto modulate the phase ditifferenee between the CW signal and a.ecmponeDt ofcopppfte:pitptt fifth beam 32.