High-Resolution Mode-Locked Laser Rangefinder With Harmonic Downconversion

1536 IEEE TRANSACTIONS ON INSTRUMENTATION AND MEASUREMENT, VOL. 61, NO. 5, MAY 2012

High-Resolution Mode-Locked Laser RangefinderWith Harmonic Downconversion

Alessandro Pesatori, Member, IEEE, Michele Norgia, Senior Member, IEEE, Cesare Svelto, Senior Member, IEEE,Massimo Zucco, Michal Stupka, and Andrea De Marchi

Abstract—The development of new pulsed optical sources withhigh pulse stability allows the improvement of common contact-less measurement techniques. A new two-way optical rangefinder,employing a femtosecond laser, is presented here from design toimplementation. The system is based on the evaluation of thephase delay of the returning optical pulse train with respect tothe outgoing one. The main idea is to expand the time intervalcorresponding to the phase delay by harmonic heterodyne down-conversion of a high harmonic of the pulse repetition rate (upto 10 GHz), which is applied symmetrically to the two channels.The system has shown 10 μm repeatability with a resolution thatimproves proportionally to the number of the employed harmonic.

Index Terms—Displacement measurement, distance measure-ment, optical components, optical distance measurements, opticalsignal detection.

I. INTRODUCTION

THE INDUSTRY request for absolute length measure-ments over long distances has been growing in recent

years, and accuracy, resolution, and measurement speed spec-ifications become increasingly more stringent [1]. Applicationfields range from aerospace industry, requiring for example 3-Dcharacterization of wing structures up to 100 m, or real-timecontrol of satellites dynamics, to earth science, e.g., in geodesicmonitoring, earthquake prediction, or critical decisions on toxicwaste storage sites.

Although, for absolute length measurements in air [2], theultimate accuracy limit is in any case the uncertainty on theaverage air refraction index along the optical path, the vari-ous existing techniques differ in resolution, speed, amount ofa priori knowledge needed for an absolute measurement, com-plexity, cost, and, most importantly, environmental robustness.

In general, two types of techniques can be identified: 1) time-of-flight (TOF) methods [3]–[5], where the length is obtainedby measuring the time taken by light to cover the distance to bemeasured, usually in round trip; and 2) interferometric methods[6], where the length is obtained by measuring the phase dif-

Manuscript received June 21, 2011; revised November 30, 2011; acceptedDecember 1, 2011. Date of publication February 14, 2012; date of currentversion April 6, 2012. The Associate Editor coordinating the review processfor this paper was Dr. George Xiao.

A. Pesatori, M. Norgia, and C. Svelto are with the Dipartimento di Elet-tronica e Informazione, Politecnico di Milano, 20133 Milan, Italy (e-mail:[email protected]).

M. Zucco and M. Stupka are with National Institute of Metrological Re-search, 10135 Turin, Italy (e-mail: [email protected]).

A. De Marchi is with the Dipartimento di Elettronica e Telecomunicazioni,Politecnico di Torino, 10129 Turin, Italy (e-mail: [email protected]).

Color versions of one or more of the figures in this paper are available onlineat http://ieeexplore.ieee.org.

Digital Object Identifier 10.1109/TIM.2012.2183437

ference accumulated by the optical wave as it propagates alongit or along a reference base line. The main difference betweenthe two is that the latter methods are based on phase velocity ofthe light wave, whereas the former are based on group velocity.As a result, a phase coherent source, a quiet environment,and uninterrupted incremental fringe counting are necessary toget absolute length measurements from the latter, whereas theformer can be employed in rougher environments and in turbu-lent air to obtain in principle an absolute measurement with asource, which does not need to be equally phase coherent. How-ever, while the latter can offer fractional wavelength resolutionwhenever interference fringes can be obtained, the former istypically limited to very low spatial resolutions by the highvalue of the speed of light as an already hard time resolution of10 ps is needed in a two-way system to achieve a length reso-lution of only 1.5 mm (1.5 10−5 on a range of 100 m).

A number of techniques were devised to overcome someof the shortcomings of either approach, mainly based on thesynthetic wave method [7], [8], which aims at relaxing thefringe counting burden in interferometry, or on averaging alarge number of measures, which aims at improving resolutionin TOF systems. An example of the latter is the rangefindingtechnique based on phase-shift measurement of RF sine-waveamplitude modulation of a CW laser [9], [10]. This techniqueachieves much better resolution than basic single-pulse TOFsystems but is much slower due to the heavy averaging pro-cedure. In some extreme cases, the two types of techniques endup being relatively close in conception, depending on the angleview under which they are considered. This is, for example,the case of systems using a femtosecond comb as an amplitudemodulated source [8], which can be considered as an extremecase of a synthetic wavelength design.

The distance measurement technique proposed in this pa-per embodies advantages of both kinds of a distance mea-surement technique, with the aim of providing fast absolutemeasurements with better resolution limits than the simplisticTOF rangefinder, of which it shares the basic measurementprinciple. Such improved resolution can be obtained with alimited amount of averaging, and the desired “absolute” qualitycan be obtained with a limited amount of a priori knowl-edge. A preliminary introduction of the instrument idea isreported in [10].

The system is based on the idea of calculating the phase delaybetween returning and outgoing pulse trains by measuring anexpanded version of the corresponding time interval, which canbe done by downconversion to a suitable beat-note frequency ina dual-channel heterodyne system. Because phase relationships

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PESATORI et al.: HIGH-RESOLUTION MODE-LOCKED LASER RANGEFINDER WITH HARMONIC DOWNCONVERSION 1537

Fig. 1. Schematic setup of the TOF rangefinder.

are maintained in such an operation, the time delay is expandedby the ratio of input to output frequency realized by the mixers.In this way, the time-interval measurement resolution obtainedwith a time-interval counter can be improved by the same factor.Of course, the back side of the coin here is the fact that ittakes longer to acquire a measure because it can take up to onefull period of the beat note. A tradeoff is then to be made be-tween measurement resolution and speed. For example, a time-interval expansion by a factor of 106 (such as that which wouldbe obtained by downconverting to 100 Hz from 100 MHz)offers improved resolution by six orders of magnitude but alsoimplies a measurement time that is six orders of magnitudelonger than what is needed to measure delay at the inputfrequency. Although such inverse proportionality of resolutionlimit to measurement time is by itself an improvement withrespect to the inverse square-root relationship existing in sys-tems based on heavy averaging, a dramatic reduction of neededmeasurement time for a given resolution can be obtained bystarting the downconversion from a much higher frequency,such as a high harmonic of the pulse repetition rate. In fact,the output downconverted beat frequency would also get thatmuch higher in this way, and the measurement time reduced bythe same amount. The net result on obtained resolution is tomove left the sigma–tau plot by a factor equal to the harmonicnumber, which is the same as moving it down by the samefactor, because of the −1 logarithmic slope.

An apparent price that is hidden in this trick is the reductionof the ambiguity range, which imposes either comparativelybetter a priori knowledge or additional provisions to remove theambiguity if a claim of accuracy of an absolute measurement issought for this kind of system. However, it is assumed here thatsuch ambiguity can be removed pretty much the same way itused to be done in old-fashioned heterodyne counters for thehigh frequency range, where a small frequency modulation wasimposed to the reference frequency and the number of the usedharmonic was calculated from the modulation transferred onresults. No further mention will then be made of this problemin this paper.

In the research prototype that was developed, the pulse-train repetition rate is 250 MHz, and harmonics up to 10 GHz(limited only by photodiode bandwidth) can be downconvertedto frequencies in the range of 100 Hz–100 kHz, dependingon the chosen tradeoff between resolution and measurementspeed. This prototype is described and discussed to somewhatgreater theoretical detail in Section II, whereas in Section III,some preliminary experimental results are given, which indicatesupport for the analysis offered in Section II.

II. MEASUREMENT PRINCIPLE AND SYSTEM SETUP

The ideal laser source choice for the realization of arangefinder based on the concepts presented in the introductionseems to be a mode-locked femtosecond laser because of thehigh-harmonic content of its frequency comb spectrum andbecause of the well-defined shape of its hyperbolic secantoptical pulses. In fact, the first feature allows the use of veryhigh harmonics by just choosing the desired one within thefrequency comb spectrum, and the second guarantees a stablephase relationship between the chosen harmonic and the funda-mental repetition rate frequency, which is basically importantfor the validity of the whole theory behind this idea. For exam-ple, the choice of a Q-switched laser as a source would not offerthe same guarantees because of the unknown pulse shape anduncertain delay between electronic command and pulse release.For the prototype that was realized, therefore, the source ofchoice was a mode-locked fiber laser at 1560 nm (M–CombFemtosecond Oscillator, MenloSystems, average power ≈10 mW), with a pulsewidth of less than 150 fs and a repetitionrate of 250 MHz. The system setup is described in Fig. 1.

The optical output of the fiber laser is collimated on thecorner cube target, which is moved by a mechanical translator(Standa 8MT-175) with a resolution of 2.5 μm. A fraction ofthe emitted light is directed onto a reference photodiode (PD1)by means of a beam splitter, and the light reflected by the targetis collected by another photodiode (PD2). Both photodetectorsare InGaAs Electro-Optics Technology, Inc. photodiodes with


Fig. 2. Stability of the repetition rate of the mode-locked laser and therubidium frequency reference, which is evaluated in terms of the square rootof the Allan variance at different sampling times.

Fig. 3. Square root of the Allan variance of the repetition rate of the frequencysynthesizer free and locked to the rubidium frequency reference, and comparedwith the rubidium oscillator.

a bandwidth of 10 GHz. The target distance is evaluated by atime delay measurement, which is made on a high harmonicof the laser repetition rate, which is downconverted to a low-frequency beat note by means of a pair of mixers.

The frequency instabilities of the mode-locked laser repeti-tion rate and the microwave synthesizer should not in principledisturb the measurement as they are in common mode for thetwo channels, at least for any averaging time longer than theexpanded time delay for sure, but were studied in some detail(see Figs. 2 and 3) if only to make sure that they would not beexceedingly large, in which case, an imperfect common modecould make troubles. As it turned out, such instabilities werevery acceptable for the free-running synthesizer and laser atthe millisecond averaging time. It was not expected that suchinstabilities would affect measurement uncertainties, and it wastherefore judged that no additional frequency stabilization wasneeded.

The optical alignment of the system needs great care becausethe laser beam shows a different spectrum as a function ofspatial position. Figs. 4 and 5 show two examples of such spec-trum, as revealed by the photodiode in two different positions. Itis shown that the low-frequency component maximum (below1 GHz) does not correspond to a maximum in the high-frequency components. We explained this effect with the pres-

Fig. 4. Pulsed laser signal revealed by the photodiode analyzed on a spectrumanalyzer.

Fig. 5. Pulsed laser signal revealed by the photodiode on a different spatialposition.

Fig. 6. Harmonics at 1 GHz downconverted to 10 kHz.

ence of a sort of a pedestal to the very narrow optical pulse(150 fs), maybe due to some fiber cladding modes of themode-locked laser. To obtain the best SNR on the detector, thephotodiodes must be aligned maximizing the high-frequencycomponents of the signal, therefore looking at the global RFspectrum, and not only at the mean power at low frequency.

To obtain higher accuracy of measurement compared witha traditional TOF rangefinder, the time lag is measured at ahigher harmonic (e.g., 10 GHz, the 40th harmonic of 250 MHz)in a detection given by the heterodyne beat with a synthesizerfrequency, which is slightly shifted compared with a higherharmonic pulse (e.g., 10.0001 GHz). By measuring the phasegap between the two sine waves at low frequencies (e.g.,


Fig. 7. (a) Impulse train from two photodiodes recorded on the oscilloscope. (b) Zoom image of the impulse train from two photodiodes recorded on oscilloscopefor a distance ΔL = 3 cm.

100 kHz), it is possible to calculate the distance to be measured.In particular, the measurement is done by calculating the phasedelay between the two isofrequential revealed harmonics usingthe following simple formula:

ΔL =1

2 · nr

c

2π· Δϕ

m · fr(1)

where c is the velocity of the light, fr is the laser repetition rate(250 MHz), m is the harmonic index (e.g., 40 for a heterodyneconversion at 10 GHz), nr is the group refractive index in airfor the laser beam with a wavelength of 1.5 μm, and Δϕ isthe phase difference between the two detected signals. Thisdifference can be calculated as Δϕ = 2πfbΔTb, where fb isthe frequency shift chosen on the synthesizer, which is typically100 or 10 kHz in our experiments, and ΔTb is the time delaybetween the optical pulses amplified by the frequency down-conversion. The factor 2 at the denominator of (1) is relatedto the fact that the optical path in this configuration double fordisplacement ΔL because the laser reflects on a corner cubeand then returns on the second photodiode. Detected signalsare fed into two double-balanced mixers with the signal comingfrom a synthesizer at different frequencies, from 1 to 10 GHz(the limit of bandwidth of photodiodes) with a small shift ofabout 10 or 100 kHz and then low-pass filtered to downconvertthe signal to this frequency, where the phase is measured withmore precision than at high frequencies. The phase and thesubsequent calculation of distance measurement is done bymeans of custom LabVIEW software calculating the phase shiftbetween the harmonics of measurement (see Fig. 6).

The price of this resolution improvement is the reduction ofthe nonambiguity range of the measurement as follows:

LNA =c

2mfr. (2)

The nonambiguity range is thus diminished of the m factorproportional to the harmonics that are locked.

The absolute distance measurement is performed first bycalculating a rough measurement working on first-harmonicphase delay; thus, to increase the accuracy of the measurement,phase delay will be measured on the downconverted higherharmonics. The lower frequency of the downconverted harmon-ics makes possible to achieve better accuracy of the phase de-lay measurement. The absolute distance measurement without

ambiguity can also be improved by using an analog network,which is trained on a telemeter signal, as described in [11].

Absolute distance measurement is calculated from the phasedelay measurement or as the temporal delay measurement ΔTb

at frequency of beating fb as follows:

ΔTb =2c· mfr

fb· ΔL. (3)

In this way, theoretically, it is possible to increase the reso-lution from some millimeters to tens of micrometers. The gainin resolution, compared with a normal rangefinder continuouswave, is equal to mfr/fb. The TOF interval is “amplified” dueto the ratio between the pulse harmonic used and the frequencyof mixing.

III. EXPERIMENTAL RESULTS

In Fig. 7, the first measurements obtained by recording thepulses measured downstream of the photodiodes for a distancepath of 3 cm (acquired by an oscilloscope with a bandwidth of500 MHz) are shown, which are useful to test the quality andconfiguration of the optical source used.

From these signals, it is possible to measure the length of theoptical path with a resolution of some millimeters limited bythe width and velocity of the pulses. To overcome these limits,the harmonics contained in these impulses are used, throughtwo mixers, to generate two downconverted sinusoids at lowfrequencies (see Fig. 6), typically 10 kHz or lower, where it ispossible to do a more accurate measurement of the phase delayand thus of the optical distance covered by the laser pulses.

The phase and the subsequent calculation of distance mea-surement, in the first part of the study, is done by means ofan electronic counter in time-interval configuration and thencommunicated and elaborated by LabVIEW software (beat fre-quency fb 10 MHz). Figs. 8–10 show some measurements per-formed in this way by locking at three different laser harmonics,respectively, i.e., 1, 2, and 3 GHz. The measured slopes (0.325,0.757, and 1.09 ns/mm) are very close to the calculated ones(0.33, 0.66, and 0.99 ns/mm), and they are proportional to theselected harmonic, as predicted by the theory. The experimentswere done until 3 GHz because the passive circuitry utilized inthis experiment (RF cables and mixers) could not work over thisfrequency.


Fig. 8. Measurement done with a 1-GHz harmonic and fb = 10 MHz. Themeasured slope is 0.325 ns/mm versus the calculated value of 0.33 ns/mm.



Phase measurement was successively calculated with a digi-tal acquisition by custom LabVIEW software (beat frequencyfb 1–100 kHz). The realized software, after a regression onthe sample points of the sinusoids, calculates the phase delaybetween the downconverted signals and, thus, the distance.Successively, to improve the measurement speed, a simpleanalog phase meter was realized through an EXOR circuit.In Figs. 11–13, some measurements obtained by this circuitare shown. The measured slopes are very similar from thetheoretical one of 6.67 × 10−4 ms/mm, confirming the goodworking of the proposed TOF rangefinder.

Fig. 11. Displacement with a step of 100 μm and fb = 10 kHz. The measuredslope is 0.65 μs/mm versus the calculated value of 0.66 μs/mm.



To choose a beat frequency that would allow a good measure-ment speed, together with a good statistical uncertainty, manymeasurements were performed at different beat frequencieswith different averaging times. The standard deviation wascalculated on 100 measurements obtained from the phase delaycalculations, performed on ten periods of the downconvertedsinusoids at 10 kHz. The calculation showed these values ofstandard deviation: 35 μm at 0.25 GHz, 18 μm at 0.5 GHz,10 μm at 1 GHz, and 12 μm at 2 GHz. This values show thetendency of the standard deviation to diminish increasing thefrequency. Above the 2-GHz harmonic, it is difficult to measurea better resolution due to the lack of SNR due to the em-ployed passive circuitry. The results are shown in Fig. 14. It isclear that increasing the frequency of beating is possible todiminish the measurement time and the uncertainty of the singlemeasurement. From 10 kHz, the uncertainty related to the mea-surement increases, and it is no longer convenient to increasethe frequency. As a matter of fact, in this paper, we propose themeasurements obtained at 1 kHz. From these measurements, it


Fig. 14. Tradeoff between uncentainty and time to perform a measurement atdifferent frequency of beating.

Fig. 15. Photo of the system setup realized for the first tests.

is possible to provide a system resolution of about 10 μm, avery good achievement for a TOF rangefinder [1].

IV. CONCLUSION

We have designed and tested a high-resolution TOFrangefinder (see Fig. 15) utilizing the phase delay measurementof the downconverted beat notes from high harmonics of afemtosecond mode-locked pulse train. A first metrological ver-ification of this new kind of a rangefinder allows measurementof absolute distance with a resolution of 10 μm and stability ofless than 100 μm, which are completely new performances for aTOF rangefinder that will permit to use it in many and differentapplications.

ACKNOWLEDGMENT

The authors would like to thank Eng. S. Bonacina,Eng. L. Pallotta, and Dr. Felice Periale for the profuse effortduring the realization of the range finder and experimental test-ing. While this paper was being finalized, we became aware ofresults obtained with a similar approach, which were publishedin Meas. Sci. Technol. 21 (2010) 15302, by N. R. Doloca,K. Meiners-Hagen, M. Wedde, F. Pollinger, and A. Abou-Zeid.The active reduction of phase errors locally generated in the

receiver is used in that work, while the ongoing development inour group aims at solving this problem with passive temperaturestabilization.

REFERENCES

[1] S. Donati, Electro-Optical Instrumentation—Sensing and Measuring WithLasers. Upper Saddle River, NJ: Prentice-Hall, 2004.

[2] G. Bönsch and E. Potulski, “Measurement of the refractive index of airand comparison with modified Edlén’s formulae,” Metrologia, vol. 35,no. 2, pp. 133–139, Apr. 1998.

[3] J. Rueger, Electronic Distance Measurement. New York: Springer-Verlag, 1990.

[4] A. Kilpelä, R. Pennala, and J. Kostamovaara, “Precise pulsed time-of-flight laser range finder for industrial distance measurements,” Rev. Sci.Instrum., vol. 72, no. 4, pp. 2197–2202, Apr. 2001.

[5] T. Araki, “Optical distance meter using a short pulse width laser diode anda fast avalanche photodiode,” Rev. Sci. Instrum., vol. 66, no. 1, pp. 43–47,Jan. 1995.

[6] J. Ye, “Absolute measurement of a long, arbitrary distance to less than anoptical fringe,” Opt. Lett., vol. 29, no. 10, pp. 1153–1155, May 2004.

[7] C. Yin, Z. Chao, D. Lin, Y. Xu, and J. Xu, “Absolute length measurementusing changeable synthetic wavelength chain,” Opt. Eng., vol. 41, no. 4,pp. 746–750, Apr. 2002.

[8] L. Rovati, U. Minoni, M. Bonardi, and F. Docchio, “Absolute distancemeasurement using comb-spectrum interferometry,” J. Opt., vol. 29, no. 3,pp. 121–127, Jun. 1998.

[9] K. Minoshima and H. Matsumoto, “High-accuracy measurement of240-m distance in an optical tunnel by use of a compact femtosecondlaser,” Appl. Opt., vol. 39, no. 30, pp. 5512–5517, Oct. 2000.

[10] M. Norgia, A. Pesatori, C. Svelto, A. De Marchi, M. Zucco, andM. Stupka, “Time of flight telemeter with picosecond modelockedlaser,” in Proc. IEEE I2MTC, Hangzhou, China, May 10–12, 2011,pp. 1066–1069.

[11] L. Gatet and H. Tap-Béteille, “Measurement range increase of a phase-shift laser rangefinder using a CMOS analog neural network,” IEEETrans. Instrum. Meas., vol. 58, no. 6, pp. 1911–1918, Jun. 2009.

Alessandro Pesatori (S’06–M’09) was born inMilan, Italy, in 1979. He received the M.Sc. degreein biomedical engineering and the Ph.D. degree ininformation engineering from Politecnico di Milano,Milan, in 2004 and 2008, respectively.

Since 2008, he has been an Assistant Professor inelectric and electronic measurements with Politec-nico di Milano. He is the author of about 50 paperspublished in international journals or internationalconference proceedings. His main research interestsinclude optical and electronic measurements with

biomedical applications, laser spectroscopy, methods of 2-D and 3-D analysesof biomedical images, and advanced automation systems.

Dr. Pesatori is a member of the Italian Association “Group of Electrical andElectronic Measurements.”

Michele Norgia (S’99–M’01–SM’09) was born inOmegna, Italy, in 1972. He received the M.S. de-gree (with honors) in electronics engineering andthe Ph.D. degree in electronics engineering from theUniversity of Pavia, Pavia, Italy, in 1996 and 2000,respectively.

Until 2004, he worked as a Postdoctoral Re-searcher with the Optoelectronics Group, Universityof Pavia. In 2006, he joined the Department ofElectronic and Information Science, Politecnico diMilano, as an Assistant Professor in electronic mea-

surements. He is the author of more than 120 papers published in internationaljournals or international conference proceedings. His main research interestsinclude optical and electronic measurements, interferometry, chaos in lasers,optical frequency standards, microelectromechanical sensors, biomedical mea-surements, and instrumentation.

Dr. Norgia is a member of the Italian Association “Group of Electrical andElectronic Measurements.”


Cesare Svelto (S’94–M’97–SM’07) was born inBari, Italy, in 1968. He received the M.S. degreein electronic engineering (cum laude) from the Uni-versity of Pavia, Pavia, Italy, in 1993 and the Ph.D.degree from the Politecnico di Milano, Milan, Italy,in 1997.

In 1996, he joined the Department of Electronicand Information Science, Politecnico di Milano, asan Assistant Professor of electronic measurementswhere, since 2002, he has been an Associate Profes-sor of electronic measurements. Since 2006, he has

been a Full Professor of electronic measurements. His main research interestsinclude the fields of optical frequency standards, phase noise measurementsand frequency stabilization of laser and electronic oscillators, biomedicalmeasurements, fluid-dynamical velocimetry, and electrooptical instrumentationand measurements.

Dr. Svelto is a Senior Member of IEEE Instrumentation and MeasurementSociety and member of the Italian Association “Group of Electrical andElectronic Measurements.” He was the recipient of the Philip Morris Prize in1997 for his Ph.D. thesis on the absolute frequency stabilization of solid-statelasers.

Massimo Zucco was born in Turin, Italy, in 1964. Hereceived the degree in physics from the University ofTurin, Turin, in 1990 and the Ph.D degree from thePolitecnico di Torino, Turin, in 1995.

From 1991 to 1996, he worked with Istituto diMetrologia Gustavo Colonnetti-Consiglio Nazionaledelle Ricerche (IMGC-CNR) [currently National In-stitute of Metrological Research (INRIM)] on laserstandards for the realization of the meter. From 1996to 1997, He worked with the National Physical Labo-ratory, Teddington, U.K., as a Research Fellow on the

realization of the caesium fountain and the Raman velocity selection apparatus.From 1998 to 2002, he worked with IMGC-CNR to carry out concentrationand spectroscopic parameter measurements. From 2002 to 2006, he workedwith the Bureau International des Poids et Mesures (BIPM), Sevres, France, onabsolute optical frequency measurements using femtosecond comb techniquesand on laser metrology. Since 2006, he has had a permanent position withthe INRIM, where he has been working on laser standards for the realizationof the definition of the meter, on femtosecond laser application to absoluteinterferometry and absolute frequency measurements, and on hyperspectralimaging.

Michal Stupka was born in Prague, Czech Republic,in 1966. He received the M.S. degree in optics andoptoelectronics from Charles University of Prague,Prague, in 1991; the DESS diploma from J. MoulinUniversity, Lyon, France, in 1996; and the Ph.D.degree from Midi-Pyrenees Observatory, Toulouse,France, in 2002.

In 1997, he joined the Department of SolarPhysics, Astronomical Institute of the Czech Acad-emy of Sciences, Ondrejov, Czech Republic. In2002, he became an R&D Specialist with the X-Ray

Laser Group, Institute of Physics, Prague, Czech Republic. In 2009, he col-laborated to metrology projects with the National Institute of MetrologicalResearch, Turin, Italy. He is the author or coauthor of 30 articles published ininternational journals or international proceedings. He has several experienceson soft X-ray laser and high-power laser applications in material sciences, inlaboratory astrophysics, and in biology and contributed to the developmentof soft X-ray lasers. His main research interests include the fields of adaptiveoptics and X-ray optics, plasma physics, and image processing.

Dr. Stupka is a member of the International Society for Optics and Photonics.In 2007, he was a Conference Chair of SPIE Europe’s Optics & OptoelectronicsCongress in Prague, Czech Republic.

Andrea De Marchi was born in 1947. He receivedthe M.S. degree in electrical engineering from thePolitecnico di Torino, Turin, Italy, in 1972.

For many years, he was with Istituto Elettrotec-nico Nazionale (now included together with Isti-tuto di Metrologia Gustavo Colonnetti into NationalInstitute of Metrological Research) and worked oncesium primary clocks with National Institute ofStandards and Technology, Boulder, CO. He was aVisiting Scientist for short periods with LaboratoirePrimaire du Temps et des Fréquences (currently

Systémes de Référence Temps-Espace), Paris, France; with Physikalisch-Technische Bundesanstalt, Braunschweig, Germany; and with National Re-search Laboratory of Metrology (currently National Institute of AdvancedIndustrial Science and Technology), Tsukuba, Japan. He is currently a Professorof electronic measurements with Politecnico di Torino. He has researched in thefield of frequency and time metrology in connection with metrological institu-tions around the world. He is the author of more than 150 papers published oninternational journals and conference proceedings. His main interests includethe study and the improvement of atomic frequency standards, particularlythose based on cesium, and general metrology, including sensor technology.

Mr. De Marchi serves on the Scientific Committees of the Frequency ControlSymposium and the European Frequency and Time Forum. He is also amember of the Governing Board of the Symposium on Frequency Standardsand Metrology, which he organized and chaired in 1988. He was the recipientof the 1991 Rabi Award “For contributions to significant improvements in theaccuracy and stability of Cesium beam frequency standards.”

High-Resolution Mode-Locked Laser Rangefinder With Harmonic Downconversion

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