Jiyong Park

Hybrid mode-locked Er-doped fiber femtosecond oscillator with 156 mW output power

We report on an Er-doped fiber oscillator that produces 146 fs pulses with 156 mW average power at a repetition rate of 49.9 MHz. The pulse energy reaches 3.13 nJ, surpassing the conventional power limit in the dispersion-managed soliton regime. Such high pulse power is obtained by devising a hybrid mode-locking scheme that combines saturable absorption with nonlinear polarization evolution. The oscillator also offers excellent temporal purity in the generated pulses with high power, providing a robust fiber-based frequency comb well suited for industrial uses.

Femtosecond laser pulses for fast 3-D surface profilometry of microelectronic step-structures.

Fast, precise 3-D measurement of discontinuous step-structures fabricated on microelectronic products is essential for quality assurance of semiconductor chips, flat panel displays, and photovoltaic cells. Optical surface profilers of low-coherence interferometry have long been used for the purpose, but the vertical scanning range and speed are limited by the micro-actuators available today. Besides, the lateral field-of-view extendable for a single measurement is restricted by the low spatial coherence of broadband light sources. Here, we cope with the limitations of the conventional low-coherence interferometer by exploiting unique characteristics of femtosecond laser pulses, i.e., low temporal but high spatial coherence. By scanning the pulse repetition rate with direct reference to the Rb atomic clock, step heights of ~69.6 μm are determined with a repeatability of 10.3 nm. The spatial coherence of femtosecond pulses provides a large field-of-view with superior visibility, allowing for a high volume measurement rate of ~24,000 mm3/s.

Coherent supercontinuum generation using Er-doped fiber laser of hybrid mode-locking

Supercontinuum generation is performed using femtosecond laser pulses produced by combining two distinct mode-locking mechanisms of nonlinear polarization evolution with saturable absorption on an Er-doped fiber oscillator. The generated supercontinuum yields a high level of spectral visibility of 93%, without the presence of spontaneous emission of post-amplification, being well suited for precision spectroscopy, broadband interferometry, and coherent telecommunications.

Femtosecond pulses for 3-D surface measurement of microelectronic step-structures

We present a fast and precise 3-D measurement of microelectronic step-structures over a wide field-of-view by utilizing high spatial coherence, low temporal coherence and repetition rate tunablility of femtosecond laser pulses.

Tuning range extension of pulse repetition rate using chirped fiber Bragg gratings

We present a fiber femtosecond laser oscillator that incorporates a pair of chirped fiber Bragg gratings (CFBGs) to augment the cavity length elongation produced by a PZT actuator. With a magnification factor of 18.2, the CFBG pair offers a 4.44 mm cavity length extension, providing a 25.59 kHz tuning range of the repetition rate from a 41.56 MHz nominal value without loss of mode locking. The extended tuning range enhances the performance of comb stabilization in uncontrolled environments and pulse-to-pulse interferometry for step height measurements.

Precision 3D surface measurement of step-structures using mode-locked femtosecond pulses

Fast, precise 3-D measurement of step-structures fabricated on microelectronic products is essential for quality assurance of semiconductor, flat panel display and photovoltaic products. Optical interferometers have long been used, but not that wide-spread for step-structures due to their phase ambiguity or low spatial coherence. Femtosecond pulse lasers can provide novel possibilities to optical profilometry both in the time and the frequency domain. In the time domain, step-surfaces can be measured over wide area by exploiting low temporal but high spatial coherence of femtosecond pulses; in the frequency domain, multi-wavelength interferometry permits the absolute measurement over the discontinued surface profiles while maintaining the sub-wavelength measurement precision.

High-precision 3-D surface measurement of step-structures using femtosecond lasers

Femtosecond pulse lasers provide novel possibilities to high-precision optical profilometry for quality assurance of step-structures on 3D microelectronic products based on its time and frequency domain characteristics.

Low-repetition-rate fiber femtosecond laser oscillator

We demonstrate a ring type, mode-locked all-normal-dispersion ytterbium-doped fiber laser which have 9.8 MHz repetition rate through the combination of saturable absorber mirror and nonlinear polarization evolution (NPE) phenomena.