• Korean Journal of Optics and Photonics
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• v.5 no.1
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• pp.60-66
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• 1994

First, the beam waist size of TE$M_{00}$ Nd:YAG laser mode with Positive Branch Unstable Resonator was calculated. and then, the output power, fundamental mode and multimode beam quality factor of PBUR were measured and compared with thouse of reference resonator with plane pallalel mirrors. In characterizing the beam quality, the $M^2$ concept was used. The focusability of laser beam in unstable resonators was discussed with this $M^2$.

• Korean Journal of Optics and Photonics
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• v.10 no.4
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• pp.311-317
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• 1999

Unidirectional single-mode operation of a diode-pumped Nd:YAG laser with a planar semimonolithic ring cavity has been demostrated at 1064 nm. The semimonolithic cavity consists of a laser active medium placed in a magnetic field, a crystal quartz plate, and an output coupling mirror. They form an optical diode by acting each part as a Faraday rotator, a reciprocal polarization rotator and a partial polarizer, respectively. An eigenpolarization theory for the cavity configuration was presented and losses for the eigenmodes were calculated. A pump-limited single-mode output power of 155 mW and a slope efficiency of 17% were obtained when the laser was pumped by a 1.2 W, 809 nm diode-laser. A laser linewidth of less than 100 kHz is inferred from a beat note frequency spectrum between two identical laser systems and continous single-mode tuning range was more than 2 GHz.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.8
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• pp.1407-1411
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• 2008

In material processing, a laser system with optimal laser parameters has been considered to be significant. Especially, the laser scribing technology is thought to be very important for fabricating DSSC(Dye sensitized solar eel!) modules with good quality. Moreover, the $TEM_{00}$ mode laser beam is the most dominant factor to decide the IPCE(Incident photon to current conversion efficiency) characteristics. In order to get the $TEM_{00}$ mode, a pin-hole is inserted within a simple pulsed Nd:YAG laser resonator. And the spatial field distribution is measured by using three size pin-hole diameters of 2.0, 6.0mm respectively. At that moment, each case has the same laser beam energy by adjusting the discharge voltage and pps(pulse per second). From those results, it is known that the pin-hole size of 2.0mm has the perfect $TEM_{00}$ mode. In addition, at the charging voltage of 1000V, 10pps and the feeding speed of 1.11mm/sec, the SEM photo of FTO(Fluorine-doped tin oxide) thin film layers shows the best scribing trace.

• Proceedings of the Optical Society of Korea Conference
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• 1989.02a
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• pp.13-19
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• 1989

Passive mode-locking of a pulsed Nd:YAG laser is achieved with saturable absorbers, BDN dye in iodoethane solvent and Kodak Eastman # 26 dye in 1,2-dichloroethane solvent, and its optimum conditions are investigated. The thickness of saturable absorbers employed in the laser mode-locking is 0.16~0.50mm. The PBR (peak-to-background ratio) measured in the oscilloscope is 79.8% in Kodak Eastman # 26 dye at the neighbourhood of the peak power, whereas the passive mode-locking with BDN dye gives PBR of 67.7%. BDN and Kodak Eastman # 26 dyes are superior in photostability over Kodak eastman # 9860 and # 9740 dyes which were used previously in passive mode-locking. From the PBR curve, we find that Kodak Eastman # 26dye is more effective than BDN dye in passive mode-locking. The spacing between the adjacent pulses of the pulse train, which depends on the laser cavity length, is measured and is found to be 7 nsec for the cavity length of 100cm.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.05a
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• pp.258-261
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• 2006

The structure of small launch vehicle can be divided into engine section and payload section. This paper introduces modal test of the payload section of small launch vehicle which is composed to satellite, PLA (Payload Adapter), VEB (Vehicle Equipment Bay), KMS (Kick Motor Support) and KM (Kick Motor). From this test, dynamic properties of the 2nd stage structure of small launch vehicle can be obtained. In this test, to simulate free-free boundary condition, test object was hung by 4 bungee cords and excited by using impact hammer Modal test data are analyzed by using TDAS(Test Data Analysis Software). As the result, modal parameters and mode shapes below 100Hz of the 2nd stage of small launch vehicle were identified.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2013.04a
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• pp.549-554
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• 2013

For the past years, higher power rating 2 stroke super long stroke diesel engines having more than 8 cylinders and larger cylinder bore are installed mainly on very large containerships to save on fuel consumption. However, these engines are prone to X-mode vibration due to $2^{nd}$ node torsional vibration or the X-type moment, particularly because of the increase in total length and height. Recently, cases of excessive X-mode vibration often occurred on engine's major components. This vibration is manifested also as secondary vibration causing failure in engine-mount large structures. This study investigated the excitations caused by the $2^{nd}$ node propulsion shafting torsional vibration that influence X-mode vibration of the main engine and practical countermeasures are proposed. An 8RT-82RT-flex 8 cylinder engine and 11S90S-ME 11 cylinder engine for a container ship was used as research model.

• Aerospace Engineering and Technology
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• v.6 no.1
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• pp.114-119
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• 2007

This paper introduces modal test of the 2nd stage structure of KSLV-I which is composed to satellite, PLA(Payload Adapter), EB(Equipment Bay), KMS(Kick Motor Support) and KM(Kick Motor) without PLF(Payload Fairing). In this test, to simulate free-free boundary condition, test object was hung by 4 bungee cords and excited by using impact hammer. From this test, dynamic properties of the 2nd stage structure of KSLV-I can be obtained. Modal test data are analyzed by using TDAS(Test Data Analysis Software). As the result, modal parameters and mode shapes below 100Hz of the 2nd stage of KSLV-I were identified.

• Proceedings of the Optical Society of Korea Conference
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• 1997.08a
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• pp.85-85
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• 1997

Czochralski 방법에 의해 육성된 Nd:YAG 단결정으로부터 CW mode의 1064nm laser를 발진시켰다. 육성된 단결정은 직경 50mm, 길이 120mm 이었으며, Nd 이온 농도는 O.2~0.9at% 이었다. 육성된 단결정 boule로 부터 결정학적 결함부위인 core 및 facet가 없는 양질의 단결정 부위를 Twyman-Green interferometer로 선빌하였다. 추출핀 부위는 절단, 가공, 연마공정 및 코팅 공정을 통해 직경 6.35mm, 길이 lOOmm의 laser rod를 제작하였다. 절단은 core drill, 또는 원통 연삭기를 사용하여 rod 형태로 가공하였으며, 상$\cdot$하면 polishing은 평행도 10", 직각도 5', 평활도 $\lambda$/10 수준까지 실험실에서 자체 가공하여 일반적인 laser 발진용 rod의 spec.을 만족시킬 수 있었다.

• The Journal of the Acoustical Society of Korea
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• v.16 no.1
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• pp.16-23
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• 1997

As analysis of the forced dynamic response and vibrational mode for the cantilevered beam is described. Experimental results are compared with the natural frequencies and vibrational modes for the cantilevered beam using the theory of Bernoulli-Euler and finite element method. We have found 1st and 2nd resonance frequency of the cantilevered beam by means of the various external frequencies, $1{\sim}70Hz$, using magnetic transducer. And we have studied the vibrational displacement at obtained resonance frequency of the cantilevered beam. The experimental results for the nodes of cantilevered beam were 0 in 1st mode and 0,0.786 in 2nd mode. close agreement between the theoretically predicted results and experimental result was obtained for the vibrational mode.

• Journal of Institute of Control, Robotics and Systems
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• v.21 no.2
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• pp.162-167
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• 2015

In this paper, we propose a F-MBE algorithm for Dual mode seeker (CCD and IIR). The MBE algorithm show improved performance at the IIR target size estimation. but the MBE can't use at Dual Mode seeker. To overcome this problem,, we apply template matching method for CCD target size information. The performance of proposed F-MBE method is tested at target intercept scenario of dual mode seeker equipped missile. The experiment results show that the proposed algorithm has the relatively improved performance.