Hee Joo Choi

Measurement of refractive index and thickness of transparent plate by dual-wavelength interference.

We developed an accurate and efficient method for measuring the refractive indices of a transparent plate by analyzing the transmitted intensity versus angle of incidence. By using two different wavelengths, we resolved the 2pi-ambiguity inherent to the phase measurement involving a thick medium, leading to independent determination of the absolute index of refraction and the thickness with a relative uncertainty of 10(-5). The validity and the accuracy of our method were confirmed with a standard reference material. Furthermore, our method is insensitive to environmental perturbations, and simple to implement, compared to the conventional index measurement methods providing similar accuracy.

Speckle noise reduction on a laser projection display via a broadband green light source

A broadband green light source was demonstrated using a tandem-poled lithium niobate (TPLN) crystal. The measured wavelength and temperature bandwidth were 6.5 nm and 100 °C, respectively, spectral bandwidth was 36 times broader than the periodically poled case. Although the conversion efficiency was smaller than in the periodic case, the TPLN device had a good figure of merit owing to the extremely large bandwidth for wavelength and temperature. The developed broadband green light source exhibited speckle noise approximately one-seventh of that in the conventional approach for a laser projection display.

Measurement of Refractive Index of Solid Medium by Critical Angle Method When Air Gap is Present

A critical angle method was used to measure the index of refraction of a solid medium when an air gap between the prism and the medium is present. The gap effect was analyzed both numerically and experimentally. Since the total internal reflection is severely disturbed by the large gap, determination of the critical angle and the resulting refractive index becomes ambiguous and inaccurate. By using an index matching fluid, we could determine the index of refraction with an uncertainty of

Instantaneous phase shifting deflectometry

{\pm}2{\times}1^{-3}

Evaluation of domain randomness in periodically poled lithium niobate by diffraction noise measurement

even when the gap is as large as 1

ENHANCED OPTICAL THIRD HARMONIC GENERATION IN THICK ORGANIC FILMS

{\mu}m

Adaptive interferometric null testing for unknown freeform optics metrology

.

Measurement of refractive index dispersion of a fused silica plate using Fabry–Perot interference

An instantaneous phase shifting deflectometry measurement method is presented and implemented by measuring a time varying deformable mirror with an iPhone ® 6. The instantaneous method is based on multiplexing phase shifted fringe patterns with color, and decomposing them in x and y using Fourier techniques. Along with experimental data showing the capabilities of the instantaneous deflectometry system, a quantitative comparison with the Fourier transform profilometry method, which is a distinct phase measuring method from the phase shifting approach, is presented. Sources of error, nonlinear color-multiplexing induced error correction, and hardware limitations are discussed.

Simultaneous multi-segmented mirror orientation test system using a digital aperture based on sheared Fourier analysis

Random duty-cycle errors (RDE) in ferroelectric quasi-phase-matching (QPM) devices not only affect the frequency conversion efficiency, but also generate non-phase-matched parasitic noise that can be detrimental to some applications. We demonstrate an accurate but simple method for measuring the RDE in periodically poled lithium niobate. Due to the equivalence between the undepleted harmonic generation spectrum and the diffraction pattern from the QPM grating, we employed linear diffraction measurement which is much simpler than tunable harmonic generation experiments [J. S. Pelc, et al., Opt. Lett.36, 864-866 (2011)]. As a result, we could relate the RDE for the QPM device to the relative noise intensity between the diffraction orders.

Measurement of principal refractive indices of birefringent wafer by analysis of Fabry–Perot interference fringes

In order to enhance optical third-harmonic generation (THG) in polymer films, we investigated linear and nonlinear optical properties of polymer films containing ethyl-violet with varying thickness. The THG intensity increased monotonically with thickness, as opposed to the theory for non-phase-matched THG in films thicker than the coherence length. By measuring the refractive indices, we found that the difference between the indices of the fundamental and the third-harmonic was smaller in thicker films. Thus, the coherence lengths for thicker films were evaluated to be larger than those for the thin films, explaining the monotonic increase of the THG signal with thickness.