The Ultra-Precision Metrology, Manufacturing and Machine Learning (UPM3) Lab, part of the Department of Mechanical Engineering at KAIST, focuses on next-generation semiconductors, secondary batteries, and aerospace laser payloads.

KAIST 기계공학과 초정밀 계측, 제조 및 기계 학습 (UPM3) 연구실은 차세대 반도체, 이차 전지 및 항공우주 레이저 탑재체에 중점을 둔다.

Plasmonic dynamics measured with frequency-comb-referenced phase spectroscopy

Free-space transfer of comb-rooted optical frequencies over an 18 km free-space link

Frequency comb transferred by surface plasmon resonance

High harmonic generation by field-enhanced femtosecond pulses in metal-sapphire nanostructure

Time-of-flight measurement with femtosecond light pulses

Plasmonic generation of ultrashort extreme-ultraviolet light pulses

High-harmonic generation by resonant plasmon field enhancement

Ultrafast laser pulses enable one-step graphene patterning on woods and leaves for green electronics

Untrasensitive anti-interference voice recognition by bio-inspired ski-attachable self-cleaning acoustic sensors

Wearable bandage-based strain sensor for home healthcare: combining 3D aerosol jet printing and laser sintering

Fully laser-patterned stretchable micro-supercapacitors integrated with soft electronic circuit components

Single-step selective laser writing of flexible photodetectors for wearable optoelectronics

All-graphene, flexible, and non-contact electronic skin

Coherent power amplification of third-order harmonics at thin-layered upconversion nanoparticles

Comb-rooted multi-channel synthesis of ultra-narrow optical frequencies of few Hz linewidth

High-brightness laser imaging with tunable speckle reduction enabled by electroactive micro-optic diffusers

Direct Preparation of Carbon Nanotube Intramolecular Junctions on Structured Substrates

Comb-referenced laser distance interferometer for industrial nanotechnology

Phase-dependent dynamic potential of magnetically coupled two-degree-of-freedom bistable energy harvester

Fourier-transform spectroscopy using an Er-doped fiber femtosecond laser by sweeping the pulse repetition rate

Testing of a femtosecond pulse laser in outer space

스마트 윈도우의 제조 방법, 스마트 윈도우 및 지능형 윈도우 시스템

우주 환경용 스마트 직물의 제조 방법, 우주 환경용 스마트 직물 및 우주 환경용 의류

재생 목재 기반 레이저 유도 그래핀 전극 기반의 터치 센서 및 가열기, 그리고 이의 제작 방법

마이크로 슈퍼커패시터의 제조 방법 및 마이크로 슈퍼커패시터

반도체 웨이퍼 두께 측정을 위한 고안정 테라헤르츠 분광기

펨토초 레이저 기반 다파장 간섭계를 활용한 고속, 고정밀 3차원 형상 측정 방법 및 장치

실리콘 웨이퍼 두께 측정을 위한 펨토초 레이저 기반의 3차 조화파 검출을 활용한 비선형 측정 방법 및 장치

OPTICAL FREQUENCY COMB-BASED TERAHERTZ FREQUENCY GENERATOR, AND OPERATING METHOD THEREOF

반도체 광 증폭기를 이용한 거리 측정 시스템 및 방법

광주파수빗 기반 테라헤르츠 주파수 생성기 및 이의 동작 방법

펨토초 레이저를 통해 제작된 박막 센서를 내장한 스마트 의치, 그 제조방법 및 건강 모니터링 시스템

광시계에 참조된 광빗기반 고안정 테라헤르츠 주파수 발생기

METHOD FOR MANUFACTURING LASER-INDUCED GRAPHENE BASED E-TEXTILE AND LASER SYSTEM IMPLEMENTING THE METHOD

LASER-INDUCED GRAPHENE DEVICE BUILT ON WOOD, AND FABRICATION METHOD THEREOF

레이저 유도 그래핀 기반 전자섬유 제조 방법, 그리고 이를 구현한 레이저 시스템

목재에 구현된 레이저 유도 그래핀 디바이스 및 이의 제작 방법

전자섬유 생산을 위한 펨토초 레이저 기반 섬유상 그래핀 생성 방법 및 장치

스마트 그린 홈 구현을 위한 펨토초-레이저-유도-그래핀 기반 센서 및 히터

극자외선 빔 생성 장치 및 방법

그래핀 분말 제조 방법

친환경 에너지 저장 전극 소재, 이의 제조방법 및 이를 포함하는 에너지저장 소자

펨토초 레이저의 광빗을 이용한 대기 중의 위상 노이즈의 자동 보상을 통한 자유공간 가간섭 광통신 장치 및 방법

다자유도 거리 측정 장치

장기간 안정성을 갖는 포화흡수체 기반의 전-편광 유지 광섬유 레이저 공진기

두 파장 레이저 간섭계를 이용한 길이 측정 장치

DEVICE AND METHOD FOR FREE SPACE COHERENT OPTICAL COMMUNICATION BY MEANS OF AUTOMATIC COMPENSATION FOR PHASE NOISE IN ATMOSPHERE USING OPTICAL COMB OF FEMTOSECOND LASER

DEVICE AND METHOD FOR PERFORMING STABILIZATION OF OVERALL FREQUENCY OF OPTICAL COMB OF FEMTOSECOND LASER BY USING OPTICAL MODE DIRECTLY EXTRACTED FROM OPTICAL COMB

Device and Method for Performing Overall Frequency Stabilization of Femtosecond Laser Optical Comb by Using Optical Modes Directly Extracted from Optical Comb

Fiber femtosecond laser oscillator with fast and wide range repetition rate scanning by using dual chirped fiber Bragg grating

처프 광섬유 브래그 격자 쌍을 이용한 광대역 고속 반복률 주사 광섬유 펨토초 레이저 공진기

비선형 편광 회전과 포화흡수체의 결합 모드잠금에 의해 생성되는 고출력 광섬유 펨토초 레이저 공진기

펨토초 레이저 기반의 위상 잠금 합성파 간섭계를 이용한 거리 측정 장치

High resolution time-of-flight distance measurement device based on femtosecond laser

펄스 레이저 반복률 주사 기반 고속 고정밀 표면형상 측정 간섭계

0．1 ∼ 30 ＭＨｚ의 반복률을 갖는 광섬유 레이저 시스템 및 이를 이용한 시편 가공

광섬유 펨토초 레이저의 모드잠금 자동화 장치

극초단 펄스 레이저와 수분 응고를 이용한 절단 장치 및 방법

깊이에 따른 개질면의 특성 조합을 통한 절단 장치

초음파를 이용한 레이저 가공장치 및 가공방법

전기장을 이용한 레이저 가공장치 및 가공방법

편광 레이저 빔 간의 간섭을 이용한 레이저 가공장치 및 가공방법

펄스 레이저의 분산 조절을 이용한 레이저 가공장치 및 가공방법

플라즈마를 이용한 레이저 가공상태 모니터링 장치 및 방법

플라즈몬 공명을 이용한 레이저 가공장치 및 가공방법

펨토초 레이저 기반 고분해능 시간비행법 거리측정장치

펨토초 레이저에 의해 나노 보이드 어레이 형성을 통한 절단방법

펨토초 펄스 레이저의 비선형 초점이동을 통한 절단방법

펨토초 펄스 레이저의 시간에 따른 광강도 조절을 통한 절단방법

펨토초 펄스 레이저 응용 ＰＺＴ 소자를 이용한 가공면 절단 방법

光周波
数発
生器を用いた絶
対
距離測定方法及びシステム

광주파수 발생기를 이용한 절대거리 측정방법 및 시스템

Polymeric biomaterials for medical implants and devices

Lasers in additive manufacturing: A review

Recent advances in laser‐induced graphene: mechanism, fabrication, properties, and applications in flexible electronics

Ultrafast laser pulses enable one‐step graphene patterning on woods and leaves for green electronics

High-harmonic generation by field enhanced femtosecond pulses in metal-sapphire nanostructure

Ultrasensitive anti-interference voice recognition by bio-inspired skin-attachable self-cleaning acoustic sensors

3D printed polycaprolactone carbon nanotube composite scaffolds for cardiac tissue engineering

Wearable bandage-based strain sensor for home healthcare: Combining 3D aerosol jet printing and laser sintering

Absolute length calibration of gauge blocks using optical comb of a femtosecond pulse laser

Absolute distance measurement by dual-comb interferometry with adjustable synthetic wavelength

Single‐step selective laser writing of flexible photodetectors for wearable optoelectronics

Green flexible graphene–inorganic‐hybrid micro‐supercapacitors made of fallen leaves enabled by ultrafast laser pulses

All-graphene-based highly flexible noncontact electronic skin

Absolute length measurement with the frequency comb of a femtosecond laser

Absolute positioning by multi-wavelength interferometry referenced to the frequency comb of a femtosecond laser

Fully laser-patterned stretchable microsupercapacitors integrated with soft electronic circuit components

Seung-Woo Kim

Truong-Son Dinh Le

Seungchul Kim

Murukeshan Vadakke Matham ( MPhil....

Joohyung Lee

Byunggi Kim

Seunghwoi Han

Sangbaek Park

Woo-Tae Park

Inkyu Park

Donghwan Kim

Seung Hwan Ko

Wai Yee Yeong

Matthias Kling

Joonhee Choi

Chee Kai Chua

KIM Young-Jin

High-harmonic generation by focusing a femtosecond laser onto a gas is a well-known method of producing coherent extreme-ultraviolet (EUV) light ,, . This nonlinear conversion process requires high pulse intensities, greater than 10 13 W cm -2 , which are not directly attainable using only the output power of a femtosecond oscillator. Chirped-pulse amplification enables the pulse intensity to exceed this threshold by incorporating several regenerative and/or multi-pass amplifier cavities in tandem , . Intracavity pulse amplification (designed not to reduce the pulse repetition rate) also requires a long cavity , . Here we demonstrate a method of high-harmonic generation that requires no extra cavities. This is achieved by exploiting the local field enhancement induced by resonant plasmons within a metallic nanostructure consisting of bow-tie-shaped gold elements on a sapphire substrate. In our experiment, the output …

In this review article, we focus on the various types of materials used in biomedical implantable devices, including the polymeric materials used as substrates and for the packaging of such devices. Polymeric materials are used because of the ease of fabrication, flexibility, and their biocompatible nature as well as their wide range of mechanical, electrical, chemical, and thermal behaviors when combined with different materials as composites. Biocompatible and biostable polymers are extensively used to package implanted devices, with the main criteria that include gas permeability and water permeability of the packaging polymer to protect the electronic circuit of the device from moisture and ions inside the human body. Polymeric materials must also have considerable tensile strength and should be able to contain the device over the envisioned lifetime of the implant. For substrates, structural properties and, at …

In recent years, additive manufacturing, also known as three-dimensional (3D) printing, has emerged as an environmentally friendly green manufacturing technology which brings great benefits, such as energy saving, less material consumption, and efficient production. These advantages are attributed to the successive material deposition at designated target areas by delivering the energy on it. In this regard, lasers are the most effective energy source in additive manufacturing since the laser beam can transfer a large amount of energy into micro-scale focal region instantaneously to solidify or cure materials in air, therefore enabling high-precision and high-throughput manufacturing for a wide range of materials. In this paper, we introduce laser-based additive manufacturing methods and review the types of lasers widely used in 3D printing machines. Important laser parameters relevant to additive manufacturing …

The time-of-flight of light pulses has long been used as a direct measure of distance 1, 2, but state-of-the-art measurement precision using conventional light pulses or microwaves peaks at only several hundreds of micrometres 3, 4. Here, we improve the time-of-flight precision to the nanometre regime by timing femtosecond pulses through phase-locking control of the pulse repetition rate using the optical cross-correlation technique 5, 6. Our experiment shows an Allan deviation of 117 nm in measuring a 0.7-km distance in air at a sampling rate of 5 ms once the pulse repetition is phase-locked, which reduces to 7 nm as the averaging time increases to 1 s. This enhanced capability is maintained at long range without periodic ambiguity, and is well suited to lidar applications such as geodetic surveying 7, range finders 8 and absolute altimeters 9. This method could also be applied to future space missions involving …

Ultrashort extreme-ultraviolet pulses are a key tool in time-resolved spectroscopy for the investigation of electronic motion in atoms , , molecules and solids. High-harmonic generation is a well-established process for producing ultrashort extreme-ultraviolet pulses by direct frequency upconversion of femtosecond near-infrared pulses ,, . However, elaborate pump–probe experiments performed on the attosecond timescale , require continuous efforts to improve the spatiotemporal coherence and also the repetition rate of the generated pulses. Here, we demonstrate a three-dimensional metallic waveguide for the plasmonic generation of ultrashort extreme-ultraviolet pulses by means of field enhancement using surface-plasmon polaritons. The intensity enhancement factor reaches a peak of ∼350, allowing generation up to the 43rd harmonic in xenon gas, with a modest incident intensity of ∼1 × 10 11 W cm –2 . The pulse …

Laser‐induced graphene (LIG) is a newly emerging 3D porous material produced when irradiating a laser beam on certain carbon materials. LIG exhibits high porosity, excellent electrical conductivity, and good mechanical flexibility. Predesigned LIG patterns can be directly fabricated on diverse carbon materials with controllable microstructure, surface property, electrical conductivity, chemical composition, and heteroatom doping. This selective, low‐cost, chemical‐free, and maskless patterning technology minimizes the usage of raw materials, diminishes the environmental impact, and enables a wide range of applications ranging from academia to industry. In this review, the recent developments in 3D porous LIG are comprehensively summarized. The mechanism of LIG formation is first introduced with a focus on laser‐material interactions and material transformations during laser irradiation. The effects of laser …

Fast, simple, cost‐efficient, eco‐friendly, and design‐flexible patterning of high‐quality graphene from abundant natural resources is of immense interest for the mass production of next‐generation graphene‐based green electronics. Most electronic components have been manufactured by repetitive photolithography processes involving a large number of masks, photoresists, and toxic etchants; resulting in slow, complex, expensive, less‐flexible, and often corrosive electronics manufacturing processes to date. Here, a one‐step formation and patterning of highly conductive graphene on natural woods and leaves by programmable irradiation of ultrafast high‐photon‐energy laser pulses in ambient air is presented. Direct photoconversion of woods and leaves into graphene is realized at a low temperature by intense ultrafast light pulses with controlled fluences. Green graphene electronic components of electrical …

Plasmonic high-harmonic generation (HHG) drew attention as a means of producing coherent extreme ultraviolet (EUV) radiation by taking advantage of field enhancement occurring in metallic nanostructures. Here a metal-sapphire nanostructure is devised to provide a solid tip as the HHG emitter, replacing commonly used gaseous atoms. The fabricated solid tip is made of monocrystalline sapphire surrounded by a gold thin-film layer, and intended to produce EUV harmonics by the inter- and intra-band oscillations of electrons driven by the incident laser. The metal-sapphire nanostructure enhances the incident laser field by means of surface plasmon polaritons, triggering HHG directly from moderate femtosecond pulses of ∼0.1 TW cm −2 intensities. The measured EUV spectra exhibit odd-order harmonics up to ∼60 nm wavelengths without the plasma atomic lines typically seen when using gaseous atoms as …

Human voice recognition systems (VRSs) are a prerequisite for voice-controlled human-machine interfaces (HMIs). In order to avoid interference from unexpected background noises, skin-attachable VRSs are proposed to directly detect physiological mechanoacoustic signals based on the vibrations of vocal cords. However, the sensitivity and response time of existing VRSs are bottlenecks for efficient HMIs. In addition, water-based contaminants in our daily lives, such as skin moisture and raindrops, normally result in performance degradation or even functional failure of VRSs. Herein, we present a skin-attachable self-cleaning ultrasensitive and ultrafast acoustic sensor based on a reduced graphene oxide/polydimethylsiloxane composite film with bioinspired microcracks and hierarchical surface textures. Benefitting from the synergetic effect of the spider-slit-organ-like multiscale jagged microcracks and the lotus …

Fabrication of tissue engineering scaffolds with the use of novel 3D printing has gained lot of attention, however systematic investigation of biomaterials for 3D printing have not been widely explored. In this report, well‐defined structures of polycaprolactone (PCL) and PCL‐ carbon nanotube (PCL‐CNT) composite scaffolds have been designed and fabricated using a 3D printer. Conditions for 3D printing has been optimized while the effects of varying CNT percentages with PCL matrix on the thermal, mechanical and biological properties of the printed scaffolds are studied. Raman spectroscopy is used to characterise the functionalized CNTs and its interactions with PCL matrix. Mechanical properties of the composites are characterised using nanoindentation. Maximum peak load, elastic modulus and hardness increases with increasing CNT content. Differential scanning calorimetry (DSC) studies reveal the thermal …

Flexible and stretchable strain sensors are in great demand for many applications like wearables and home health. This work reports a strain sensor fabricated using aerosol jet printing technology on a commercially available bandage to be used as a low-cost wearable. Laser light is explored to sinter the silver nanoparticle ink on a low-temperature bandage substrate. The laser parameters, their effects on the microstructure of the film, and the resulting sensor performance are systematically investigated. The results showed that the sensor is stretchable and has good sensitivity and stability for 700 cycles of repeated bending.

We report an exploitation of the optical comb of a femtosecond pulse laser as the wavelength ruler for the task of absolute length calibration of gauge blocks. To that end, the optical comb was stabilized to the Rb clock of frequency standard and an optical frequency synthesizer was constructed by tuning an external single-frequency laser to the optical comb. The absolute height of gauge blocks was measured by means of multi-wavelength interferometry using multiple beams of different wavelengths consecutively provided by the optical frequency synthesizer. The wavelength uncertainty was measured 1.9 × 10^-10 that leads to an overall calibration uncertainty of 15 nm (k=1) in determining the absolute length of gauge blocks.

Absolute distances were measured using two femtosecond lasers of different pulse repetition rates by revisiting the dual-comb interferometric method proposed by Coddington et al (2009 Nature Photon. 3 351–6). The apparatus built for experiments was designed to eliminate the dead zones in the measurement range by separating the measurement pulses from the reference pulses using orthogonal polarization. In addition, the pulse repetition rate of the signal laser was made tunable in order to extend the non-ambiguity range (NAR) by adaptively adjusting the synthetic wavelength in consideration of the de facto measurement stability in the air. Actual tests performed in the open air proved that a target distance of 69.3 m is measured without interruptions at a 200 µs update rate in the presence of a∼ 170 µm drift of the optical path length caused by the fluctuation of the refractive index of air. The proposed …

The increasing demand for wearable optoelectronics in biomedicine, prosthetics, and soft robotics calls for innovative and transformative technologies that permit facile fabrication of compact and flexible photodetectors with high performance. Herein, by developing a single‐step selective laser writing strategy that can finely tailor material properties through incident photon density control and lead to the formation of hierarchical hybrid nanocomposites, e.g., reduced graphene oxide (rGO)–zinc oxide (ZnO), a highly flexible and all rGO–ZnO hybrid‐based photodetector is successfully constructed. The device features 3D ultraporous hybrid films with high photoresponsivity as the active detection layer, and hybrid nanoflakes with superior electrical conductivity as interdigitated electrodes. Benefitting from enhanced photocarrier generation because of the ultraporous film morphology, efficient separation of electron–hole …

The development of green flexible micro‐supercapacitors (MSCs) is one of the biggest challenges in future wearable electronics. Flexible MSCs are mainly produced from non‐biodegradable synthetic polymers, resulting in massive electronic waste. Moreover, complex multi‐step fabrication increases their production cost. Here, the direct fabrication of highly conductive, intrinsically flexible, and green microelectrodes from naturally fallen leaves in ambient air using femtosecond laser pulses without any additional materials is reported. Hierarchically porous graphene is patterned on different types of leaves via a facile, mask‐less, scalable, and one‐step laser writing. Leaves consist of biominerals, which decompose into inorganic crystals that serve as nucleation sites for the growth of 3D mesoporous few‐layer graphene. The femtosecond laser‐induced graphene (FsLIG) microelectrodes formed on leaves have …

Noncontact electronic skin (e-skin), which possesses superior long-range and high-spatial-resolution sensory properties, is becoming indispensable in fulfilling the emulation of human sensation via prosthetics. Here, we present an advanced design and fabrication of all-graphene-based highly flexible noncontact e-skins by virtue of femtosecond laser direct writing (FsLDW). The photoreduced graphene oxide patterns function as the conductive electrodes, whereas the pristine graphene oxide thin film serves as the sensing layer. The as-fabricated e-skins exhibit high sensitivity, fast response–recovery behavior, good long-term stability, and excellent mechanical robustness. In-depth analysis reveals that the sensing mechanism is attributed to proton and ionic conductivity in the low and high humidity conditions, respectively. By taking the merits of the FsLDW, a 4 × 4 sensing matrix is facilely integrated in a single …

We report exploiting the frequency comb of a femtosecond laser as a means of realizing the time-based SI definition of the meter for length metrology. Specifically, an external-cavity diode laser is continuously tuned to a stabilized frequency comb, and its output frequency is modulated over an extensive range to measure the absolute value of a given length by means of multi-wavelength optical interferometry. This approach could find applications in establishing practical length standards with a small amount of uncertainty directly traceable to time standards.

We report a test operation of an Er-doped fibre femtosecond laser which was conducted for the first time in outer space. The fibre-based ultrashort pulse laser payload was designed to meet space-use requirements, undergone through ground qualification tests and finally launched into a low-earth orbit early in 2013. Test results obtained during a one-year mission lifetime confirmed stable mode-locking all the way through although the radiation induced attenuation (RIA) in the Er-doped gain fibre caused an 8.6% reduction in the output power. This successful test operation would help facilitate diverse scientific and technological applications of femtosecond lasers in space and earth atmosphere in the near future.

A multi-wavelength interferometer utilizing the frequency comb of a femtosecond laser as the wavelength ruler is tested for its capability of ultra-precision positioning for machine axis control. The interferometer uses four different wavelengths phase-locked to the frequency comb and then determines the absolute position through a multi-channel scheme of detecting interference phases in parallel so as to enable fast, precise and stable measurements continuously over a few meters of axis-travel. Test results show that the proposed interferometer proves itself as a potential candidate of absolute-type position transducer needed for next-generation ultra-precision machine axis control, demonstrating linear errors of less than 61.9 nm in peak-to-valley over a 1-meter travel with an update rate of 100 Hz when compared to an incremental-type He-Ne laser interferometer.

Stretchable energy storage devices are prerequisites for the realization of autonomous elastomeric electronics. Microsupercapacitors (MSCs) are promising candidates for this purpose due to their high power and energy densities, potential for miniaturization, and feasibility of embedding in circuits; however, efforts to realize stretchable MSCs have mostly relied on strain-accommodating materials and have suffered from limited stretchability, low conductivity, or complicated patterning processes. Here, we designed and fabricated a stretchable MSC based on reduced-graphene-oxide/Au heterostructures patterned by facile and versatile direct laser patterning. An interconnected and stable 3D network composed of vertically oriented heterostructures was realized by high-repetition-rate femtosecond laser pulses. Upon transferring to polydimethylsiloxane (PDMS), the 3D network achieved a high conductivity of ~10 5 S …

School of Mechanical and Aerospace Engineering

KAIST Institute for Optical Science and Technology (Jointly Appointed)

Ultrafast Optics for Ultraprecision Group, Department of Mechanical Engineering

Quantum Electronics & Photonics Division, Physical Measurement Laboratory

Ultrafast Optics for Ultraprecision Engineering Research Group

Billionth Uncertainty Precision Engineering Research Group

Lengths and Dimensions Division, Length Standards Section

Tenured Associate Professor, Director

Measurement technologies for precision positioning

Thickness-profile measurement of transparent thin-film layers by white-light scanning interferometry

Absolute distance measurement by dispersive interferometry using a femtosecond pulse laser

An ultraprecision stage for alignment of wafers in advanced microlithography

Improvement of scanning accuracy of PZT piezoelectric actuators by feed-forward model-reference control

Polarization-sensitive optical coherence tomography for photoelasticity testing of glass/epoxy composites

General algorithm of phase-shifting interferometry by iterative least-squares fitting

Combs rule

Distance measurements by combined method based on a femtosecond pulse laser

Numerical correction of reference phases in phase-shifting interferometry by iterative least-squares fitting

Young-Jin KIM

Jonghan Jin

Byung Jae Chun

Yoon-Soo Jang

Ki-Nam Joo

HyunJay Kang

Young-Sik Ghim

Wei Gao

KIM Seung-Woo

Precision positioning of an object relative to a reference point is a common task in many activities of production engineering. Sensor technologies for single axis measurement, either linear or rotary, which form the fundamentals of measurement technologies for precision positioning, are reviewed. Multi-axis coordinate measurement methods such as triangulation and multilateration, as well as Cartesian and polar systems for specifying the position in a plane or three-dimensional (3D) space are then presented, followed by a discussion on traceability and standards. Some advanced applications of measurement technologies for precision positioning in manufacturing industries are also demonstrated.

White-light scanning interferometry is increasingly used for precision profile metrology of engineering surfaces, but its current applications are limited primarily to opaque surfaces with relatively simple optical reflection behavior. A new attempt is made to extend the interferometric method to the thickness-profile measurement of transparent thin-film layers. An extensive frequency-domain analysis of multiple reflection is performed to allow both the top and the bottom interfaces of a thin-film layer to be measured independently at the same time by the nonlinear least-squares technique. This rigorous approach provides not only point-by-point thickness probing but also complete volumetric film profiles digitized in three dimensions.

We describe an interferometric method that enables to measure the optical path delay between two consecutive femtosecond laser pulses by way of dispersive interferometry. This method allows a femtosecond laser to be utilized as a source of performing absolute distance measurements to unprecedented precision over extensive ranges. Our test result demonstrates a non-ambiguity range of ~1.46 mm with a resolution of 7 nm over a maximum distance reaching ~0.89 m.

We present an ultraprecision stage specially designed to align wafers for the microlithography of integrated circuit patterns of sub-0.3 μm design rules. The whole stage mechanism is composed of two individually operating xyθ-stages: a global stage to provide initial coarse alignment of wafers in stepping mode; and a micro stage to produce fine controlability in nanometer range. The global stage is configured with three linear motors kinematically linked to produce xyθ-motions without resorting to precision guideways. The micro stage corrects positional errors in the global stage by activating three piezoelectric microactuators housed in an elastic flexure. These two stages are simultaneously controlled as a dual servo system, because the main emphasis is given to achieving an overall positioning reproducibility of 20 nanometers in xyθ-motions in aligning wafers of 200-mm size.

For ultraprecision, three-dimensional surface metrology such as atomic force microscopy, PZT ceramic actuators are populary used to scan a testpiece in the lateral directions while its vertical dimension is traced by a measuring probe. In this type of scanning microscopy, the measuring accuracy in lateral dimensions is critically limited by hysteresis errors in PZT ceramics when operated by simple open-loop control. We describe a feed-forward control method to effectively reduce scanning errors by using deterministic hysteresis path models. Experimental results prove that this method can enhance scanning accuracy by an order of 10 as compared with conventional open-loop scanning.

We measure the spatial distribution of the mechanical stress induced inside translucent glass/epoxy composites by means of polarization-sensitive optical coherence tomography. The Stokes parameters determined from two orthogonal polarization components of the backscattered light allow the internal stress to be identified in terms of its magnitude and principal direction based on a birefringence light scattering model of glass/epoxy composites. Measurement examples show the particular case of stress concentration near a through hole and the internal structural damages caused by excessive tensile loading.

A new numerical phase-measuring algorithm for digital phases-hifting interferometry is presented. In this algorithm, the actual values of phase shifts are taken as unknowns together with the wavefront phases ultimately to be determined, and they are computed through iterative spatial and serial least-squares fittings. The algorithm is more general than existing methods in that any arbitrary number of unequal phase shifts may be adopted with no prescriptive restrictions on their spacings. The algorithm is therefore found inherently free from any errors of phase shifts, allowing accurate measurement even in harsh environmental conditions with vibratory disturbances.

The ability to measure distances with high precision is of fundamental importance. Femtosecond optical frequency combs offer an intriguing solution to the problem and could prove invaluable in space satellite missions of the future.

We describe a combined interferometric scheme that enables absolute distance measurements using a femtosecond pulse laser. This method is combined with synthetic wavelength interferometry (SWI), time of flight (TOF) and spectrally-resolved interferometry (SRI) using the optical comb of femtosecond laser. Each technique provides distinct measuring resolutions and ambiguity ranges which are complementary to each other. These separate measurement principles are incorporated and implemented simultaneously and the unified output can enhance the dynamic range of the measuring system. Our experimental results demonstrate an example of absolute distance measurement with the proposed technique and we discuss the possibility of the combined method to measure long distances and the important factors for the implementation.

We present a new computational algorithm of phase-shifting interferometry that can effectively eliminate the uncertainty errors of reference phases encountered when we obtain multiple interferograms. The algorithm treats the reference phases as additional unknowns and we determine their exact values by analyzing interferograms using the numerical least-squares technique. A series of simulations prove that this algorithm can improve measuring accuracy because it is unaffected by the nonlinear and random errors of phase shifters.

UPM3 Lab

교수님 소개

김영진

연구실 소개

연구실 키워드

알럼나이가 간 회사

연구실 지원 방법

대우 조건

연도별 논문 인용수

저널 & 학회 논문 출판 수

연구실 논문 목록

Plasmonic dynamics measured with frequency-comb-referenced phase spectroscopy

Free-space transfer of comb-rooted optical frequencies over an 18 km free-space link

Ultrafast laser pulses enable one-step graphene patterning on woods and leaves for green electronics

연구실 보유 특허

대학별 입시끈

우리 연구실 모집

교수님 소개

김영진

연구실 키워드

알럼나이가 간 회사

연구실 지원 방법

대우 조건

연도별 논문 인용수

저널 & 학회 논문 출판 수

연구실 논문 목록

Plasmonic dynamics measured with frequency-comb-referenced phase spectroscopy

Free-space transfer of comb-rooted optical frequencies over an 18 km free-space link

Ultrafast laser pulses enable one-step graphene patterning on woods and leaves for green electronics

연구실 보유 특허

최근 3년간 연구실적 높은 연구실

대학별 입시끈

우리 연구실 모집