• 제어로봇시스템학회:학술대회논문집
• /
• 1993.10a
• /
• pp.883-888
• /
• 1993

This paper proposes a monitoring method using an infrared temperature sensor in laser surface hardening process. To investigate the validity of the method a series of experiments are performed for various conditions. The experimental results show that the surface temperature depends upon the laser power, travelling speed and surface conditions of a specimen. Especially, the laser surface hardening process is greatly influenced by the surface conditions of the specimen, such as coating thickness and materials.

• Proceedings of the Optical Society of Korea Conference
• /
• 2002.07a
• /
• pp.116-117
• /
• 2002

In recent years, there has been an increasing interest in $Tm^{3+}$ doped crystals and glasses due to their potential applications as near infrared lasers and infrared to visible upconversion lasers for use in different fields such as medical surgery, eye safe laser radar, data storage, barcode reading and so on. Thulium ions have stable excited levels suitable for emitting blue upconversion fluorescence. (omitted)

• Proceedings of the Optical Society of Korea Conference
• /
• 2009.02a
• /
• pp.483-484
• /
• 2009

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2008.06a
• /
• pp.405-406
• /
• 2008

• Current Optics and Photonics
• /
• v.7 no.6
• /
• pp.738-744
• /
• 2023

Graphene-based saturable absorbers (SAs) are widely used as laser mode-lockers at various laser oscillators. In particular, transmission-type graphene-SAs with ultrabroad spectral coverage are typically manufactured on transparent substrates with low nonlinearity to minimize the effects on the oscillators. Here, we developed two types of transmitting graphene SAs based on CaF₂ and ZnSe. Using the graphene-SA based on CaF₂, a passively mode-locked mid-infrared Cr:ZnS laser delivers relatively long 540 fs pulses with a maximum output power of up to 760 mW. In the negative net cavity dispersion regime, the pulse width was not reduced further by inhomogeneous group delay dispersion (GDD) compensation. In the same laser cavity, we replaced only the graphene-SA based on CaF₂ with the SA based on ZnSe. Due to the additional self-phase modulation effect induced by the ZnSe substrate with high nonlinearity, the stably mode-locked Cr:ZnS laser produced Fourier transform-limited ~130 fs near 2,340 nm. In the stable single-pulse operation regime, average output powers up to 635 mW at 234 MHz repetition rates were achieved. To our knowledge, this is the first attempt to achieve shorter pulse widths from a polycrystalline Cr:ZnS laser by utilizing the graphene deposited on the substrate with high nonlinearity.

• Bulletin of the Korean Chemical Society
• /
• v.13 no.5
• /
• pp.553-556
• /
• 1992

The ${CO}_2$ laser absorption measurement of ${CH}_3{CH}_2Br$ utilizing photoacoustic (PA) technique was performed using a cw and a pulsed ${CO}_2$ lasers. The absorption profile in the ${CO}_2$ laser wavelength region (9-10 ${\mu}$m) and the macroscopic small signal absorption cross section at 10P(20) (10.59 ${\mu}$m, 944 $cm^{-1}$) laser line were measured using a cw ${CO}_2$ laser. The laser fluence dependence on infrared multiphoton absorption (IRMPA) was also studied with a pulsed TEA ${CO}_2$ laser at 10P(20) laser line. In view of monotonic increase of PA signal with the rise of laser fluence, it was suggested that the anharmonicity in pumped vibration mode did not restrict ir multiphoton absorption in ${CH}_3{CH}_2Br$ system as found in large molecular system.

• Current Optics and Photonics
• /
• v.7 no.6
• /
• pp.708-713
• /
• 2023

A robust all-fiber nonlinear amplifying loop-mirror-based mode-locked femtosecond laser is demonstrated. Power-dependent nonlinear phase shift in a Sagnac loop enables stable and power-efficient mode-locking working as an artificial saturable absorber. The pump power is adjusted to achieve the lowest intensity noise for stable long-term operation. The minimum pump power for mode-locking is 180 mW, and the optimal pump power is 300 mW. The lowest integrated root-mean-square relative intensity noise of a free-running mode-locked laser is 0.009% [integration bandwidth: 1 Hz-10 MHz]. The long-term repetition-rate instability of a free-running mode-locked laser is 10^-7 over 1,000 s averaging time. The repetition-rate phase noise scaled at 10-GHz carrier is -122 dBc/Hz at 10 kHz Fourier frequency. The demonstrated method can be applied as a seed source in high-precision real-time mid-infrared molecular spectroscopy.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.37 no.9
• /
• pp.807-814
• /
• 2013

A fundamental study on laser-tissue interaction was conducted with the aim of developing a therapeutic medical device that can remove lesions on the intestinal wall by irradiating a high-power 808-nm infrared laser light incorporated in an endoscopic system. The perforation depth was linearly increased in the range of 1~4 mm in proportional to laser output (3~12 W) and irradiation time (5~20 s). We demonstrated that the perforation depth during laser irradiation was varied according to the tissue property of each extracted porcine organ. The measurement of the temperature distribution suggests that the energy is localized in the irradiation spot and transferred to deep tissue, which protects the surrounding tissue from thermal injury. These results can be used to set the driving parameters for a laser incision technique as an alternative to conventional surgical interventions.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2006.05a
• /
• pp.35-36
• /
• 2006

In Nd:YAG laser welding, evaluation methods of welding flaw are various. But, the method due to fume shape is difficult to classification of welding flaw. The Nd:YAG laser process is known to have high speed and deep penetration capability to become one of the most advanced welding technologies. At the present time, some methods are studied for measurement of fume shape by using high-speed camera and photo diode. This paper describes the machining characteristics of SM45C carbon steel welding by use of an Nd:YAG laser. In spite of its good mechanical characteristics, SM45C carbon steel has a high carbon contents and suffers a limitation in the industrial application due to the poor welding properties. In this study, fume shape was measured by infrared thermal camera that is non-contact/non-destructive thermal measurement equipment through change of laser generating power, speed, focus. Weld was performed on bead-on method. Measurement results are compared as two equipments. Here, two results are composed of measurement results of fume quantities due to fume shape by infrared thermal camera and inspection results of weld bead include weld flaws by ultrasonic inspector.

• Journal of the Korea Institute of Military Science and Technology
• /
• v.26 no.1
• /
• pp.22-30
• /
• 2023

When tracking small UAVs and drone targets in cloud clutter environments, MWIR sensors are often unable to track targets continuously. To overcome this problem, the SWIR sensor is mounted on the same gimbal. Target tracking uses sensor information fusion or selectively applies information from each sensor. In this case, parallax correction using the target distance is often used. However, it is difficult to apply the existing method to small UAVs and drone targets because the laser rangefinder's beam divergence angle is small, making it difficult to measure the distance. We propose a tracking method which needs not parallax correction of sensors. In the method, images from MWIR and SWIR sensors are captured simultaneously and a tracking error for gimbal driving is chosen by effectiveness measure. In order to prove the method, tracking performance was demonstrated for UAVs and drone targets in the real sky background using MWIR and SWIR image sensors.