• Journal of the Korean Society for Precision Engineering
• /
• v.27 no.6
• /
• pp.7-16
• /
• 2010

Physical fundamentals of ultrashort femtosecond lasers are addressed along with emerging applications for precision manufacturing and metrology. Femtosecond lasers emit short pulses whose temporal width is in the range of less than a picosecond to a few femtoseconds, thereby enabling extremely high peak-power machining with less thermal damages. Besides, the broad spectral bandwidth of femtosecond lasers constructed in the form of frequency comb permits absolute distance measurements leading to ultraprecision positioning control and dimensional metrology.

• Korean Journal of Optics and Photonics
• /
• v.1 no.1
• /
• pp.87-97
• /
• 1990

With the recent advent of various ultrashort pulse lasers, time-resolved laser spectroscopic techniques have been widely recognized as versatile tools to study ultrafast phenomena in many research areas. These techniques are currently being employed not only to study atomic and molecular physics but to characterize the excited state or the carrier dynamics on surfaces of semiconductors, metals and thin layer materials. Also the sweetching speed measurement of ultrafast electro-optic devices using ultrashort laser pulses becomes important in high-speed electronics. Here, some principles of spectroscopic techniques with ps or fs lasers and their applications are summarized briefly.

• Journal of the Korean Society for Precision Engineering
• /
• v.27 no.2
• /
• pp.7-12
• /
• 2010

Due to the extremely short interaction time (< $10\times10^{-12}$sec) between laser pulse and material, which enables the minimization of heat affection, ultrafast laser micro-machining has rapidly widened its applications. In this paper, the characteristics of ultrafast laser micro-machining have been reviewed and experimentally demonstrated in laser drilling of silicon wafer and in laser cutting of rigid PCB.

• Proceedings of the Optical Society of Korea Conference
• /
• 2006.02a
• /
• pp.89-90
• /
• 2006

• Journal of Mechanical Science and Technology
• /
• v.19 no.6
• /
• pp.1378-1389
• /
• 2005

This work provides the fundamental knowledge of energy transport characteristics during very short-pulse laser heating of semiconductors from a microscopic viewpoint. Based on the self-consistent hydrodynamic equations, in-situ interactions between carriers, optical phonons, and acoustic phonons are simulated to figure out energy transport mechanism during ultrafast pulse laser heating of a silicon substrate through the detailed information on the time and spatial evolutions of each temperature for carriers, longitudinal optical (LO) phonons, acoustic phonons. It is found that nonequilibrium between LO phonons and acoustic phonons should be considered for ultrafast pulse laser heating problem, two-peak structures become apparently present for the subpicosecond pulses because of the Auger heating. A substantial increase in carrier temperature is observed for lasers with a few picosecond pulse duration, whereas the temperature rise of acoustic and phonon temperatures is relatively small with decreasing laser pulse widths. A slight lagging behavior is observed due to the differences in relaxation times and heat capacities between two different phonons. Moreover, the laser fluence has a significant effect on the decaying rate of the Auger recombination.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2003.07b
• /
• pp.1094-1097
• /
• 2003

In this paper, the cavity-length-dependent spectral and temporal characteristics of a V-groove AlGaAs-GaAs quantum wire (QWR) laser at each subband were investigated. At short cavity lasers less than $300{\mu}m$, a discrete wavelength switching from the n=1 to the n=2 subband occurred due to the increased threshold gain, resulting from the increased cavity loss. Using the characteristic of the wavelength shift from n=1 to the n=2 subband with shortening the cavity length, ultrafast lasing behaviors under gain switching at the n=1 and the n=2 subband transition were demonstrated and compared.

• Proceedings of the Optical Society of Korea Conference
• /
• 2001.02a
• /
• pp.54-55
• /
• 2001

Recently, there has been much interests in InGaN/GaN multiple-quantum-well (MQW) structures due to their applicability as optoelectronic devices such as light-emitting diodes (LEDs) and laser diodes [1]. Their ultrafast and physical properties are also of significant interests. Anomalously large acoustic phonon oscillations have been observed using ultrafast lasers in InGaN MQWs [2]. In this study, we have peformed femtosecond pump-probe experiments in the reflection geometry on 5 periods InGaN/GaN MQW LED structure with well width of 20$\AA$ and barrier width of 100$\AA$ at room temperature. (omitted)

• Proceedings of the Optical Society of Korea Conference
• /
• 2000.02a
• /
• pp.24-25
• /
• 2000

After the invention of the femtosecond pulse lasers, generating and detecting the coherent optical phonons in various materials became possible. In bulk GaAs, which is a polar material, the coherent LO phonons are known to be generated by the ultrafast screening of the surface space-charge fields. However, little is known about the generation mechanisms of coherent phonons in GaAs quantum structures. (omitted)

• Journal of Photoscience
• /
• v.6 no.3
• /
• pp.123-128
• /
• 1999

Dynamics of many ultrafast processes are markedly slowed down in various organized molecular assemblies compared to ordinary liquids. We will show that the solvation dynamics of water molecules is affected amost dramatically and is retarded by 3 ∼4 orders of magnitude in microemulsions, micells and lipids. We will also discuss how the access to fewer water molucules and the drastically altered local pH in an organized asembly affected the excited state proton transfer processes. Finally, we will show how surface second haromonic generation can be used to study the air-water surface.

• Journal of the Microelectronics and Packaging Society
• /
• v.21 no.2
• /
• pp.53-57
• /
• 2014

Thin glass (< 100 microns) is a promising material from which advanced interposers for high density electrical interconnects for 2.5D chip packaging can be produced. But thin glass is extremely brittle, so mechanical micromachining to create through glass vias (TGVs) is particularly challenging. In this article we show how laser processing using deep UV excimer lasers at a wavelength of 193 nm provides a viable solution capable of drilling dense patterns of TGVs with high hole counts. Based on mask illumination, this method supports parallel drilling of up over 1,000 through vias in 30 to $100{\mu}m$ thin glass sheets. (We also briefly discuss that ultrafast lasers are an excellent alternative for laser drilling of TGVs at lower pattern densities.) We present data showing that this process can deliver the requisite hole quality and can readily achieve future-proof TGV diameters as small $10{\mu}m$ together with a corresponding reduction in pitch size.