• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2005.10a
• /
• pp.188-191
• /
• 2005

A common feature in various methods of optical interferometry for absolute distance measurements is the use of multiple monochromatic light components either in sequence or in parallel at the same time. Two or multiple wavelength synthesis has been studied though its performance is vulnerable to the frequency instability of the light source. Recently continuous frequency modulation is considered a promising method with availability of wide band tunable diode lasers, which also have frequency instability errors. We can lock frequencies of these third-party light sources to the modes of the femtosecond laser which is stabilized to the precision of the standard radio frequency. To this end, we have stabilized all the modes of the femtosecond laser to the atomic frequency standard by using powerful tools of frequency-domain laser stabilization.

• The Transactions of the Korean Institute of Electrical Engineers C
• /
• v.53 no.11
• /
• pp.583-588
• /
• 2004

We stabilized the frequency and power of a high voltage excited CW CO2 laser on the peak of the Doppler broadened gain curve using the photoacoustic effect generated from the laser itself. The photoacoustic signal is directly coupled from an radio frequency discharge chamber via a capacitor microphone into a detector and a lock-in stabilizer. The frequency stability is estimated to be better then 1.2×10/sup -7/ at the transition P(20) line. The stabilized output power variation was reduced to from 77 % to 3.3 %.

• Journal of the Optical Society of Korea
• /
• v.2 no.1
• /
• pp.1-4
• /
• 1998

The second harmonic light of an 842 nm diode laser was generated from a KNbO3 crystal in an external ring resonator. The power of the second harmonic light was about 0.8 mV at an input fundamental power of 87 mW. The laser frequency was stabilized to the resonance frequency of the ring resonator, and the frequency fluctuation was measured as about 3 MHz.

• Proceedings of the Optical Society of Korea Conference
• /
• 2009.10a
• /
• pp.241-242
• /
• 2009

Characterics of carrier-envelope-offset frequency ($f_{ceo}$) of a femtosecond laser stabilized by the direct locking method were investigated using two f-to-2f interferometers. The stability of $f_{ceo}$ was comaparable to that achieved with a conventional PLL method.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2005.10a
• /
• pp.922-925
• /
• 2005

This article describes a FM modulation algorithm to increase the measurement speed by increasing the beat frequency of the laser without acousto-optic modulator(AOM) in the heterodyne laser interferometer. The proposed algorithm can increase the beat frequency of the heterodyne laser which limit the measurement speed by adjusting a carrier frequency through electronic circuit, while AOM is used to shift the frequency of the heterodyne laser in conventional method. Electronic circuit is constructed to modulate the signals from a laser interferometer and a waveform generator. The brier analysis, the measurement scheme of the system, and the experimental results using a Zeeman-stabilized He-Ne laser are presented. They demonstrate that the proposed algorithm is proven to enhance the measurement speed limit by increasing the beat frequency of the heterodyne laser.

• Journal of Institute of Control, Robotics and Systems
• /
• v.11 no.6
• /
• pp.496-501
• /
• 2005

This paper presents experimental results of the frequency offset locking of He-Ne lasers and the stability analysis. The master laser is free running, and the slave laser is a single-mode operating laser. The frequency difference of two lasers is stabilized to 200 MHz which can be synchronized using PLL servo. The measured beat frequency between two lasers was 200.004 MHz ${\pm}$ 0.15 MHz. The square root of Allan variance as a measure of stability in time domain is also measured. The long-term stability of the beat was worse than sort-term stability. With a gate time $\tau=1000\;s$, the square root of Allan variance was about 1 GHz. The results of the square root of Allan variance of the stabilized beat signal was a gate time of $\tau=1000\;s$, the square root of Allan variance was about 1.5 kHz. The long-term stability was improved by more than several hundred times compared with that without the stabilization.

• Proceedings of the Optical Society of Korea Conference
• /
• 2004.07a
• /
• pp.40-41
• /
• 2004

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 1997.10a
• /
• pp.214-219
• /
• 1997

We propose a new scheme of high-resolution heterodyne interferometer that employs the two-axial mode He-Ne laser with an inter-mode beat frequency of 600-1000 MHz. An electronic RF-heterodyne circuit lowers the beat frequency down to 5 MHz, so that the phase change of the interferometer output is precisely measured with a displacement resolution of 0.1 nanometer without significant loss of dynamic bandwidth. A thermal control scheme is adopted to stabilize the cavity length with aims to suppress frequency drifts caused by the phenomena of frequency pulling and polarization anisotropy of the two-axial mode laser to a stability level of 2 parts in $10^9$. The two-axial mode HeNe laser yields a high output power of 2.0 mW, whlch allows us to perform multiple measurements of up to 10 machine axes simultaneously.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2003.06a
• /
• pp.260-263
• /
• 2003

Lasers are used as the source of the interferometers in the industrial field. These lasers need 2 requirements. The first is the narrow linewidth of laser for the long coherence length. The second is the stabilized frequency of laser for the precision measurement. Now HeNe lasers are mostly used and the frequency stability is about 10$^{-9}$ . In this paper, we construct the HeNe laser systems of frequency stabilization using typical 2 method, the beat frequency stabilization method and the intensity difference method. So, we get the frequency stabilities of 2.01$\times$10$^{-9}$ (0.1s), 3.4$\times$10$^{-9}$ (0.1s).

• Korean Journal of Optics and Photonics
• /
• v.15 no.6
• /
• pp.569-574
• /
• 2004

We stabilized the frequency and power of a CW radio-frequency-excited $CO_2$ laser on the peak of the Doppler broadened gain curve using the photoacoustic effect generated from the laser itself. The condenser microphone is installed in the radio frequency discharge chamber to detect a photoacoustic signal. The photoacoustic signal is fed to a lock-in stabilizer as a reference signal for stabilization. The frequency stability is estimated to be better then 5.4${\times}$10$^{-8}$ at the P(20) line. The stabilized output variation was reduced 9.3%, compared to 100% for a free running laser.