Transport-of-intensity-based phase imaging to quantify the refractive index response of 3D direct-write lithography

Abstract

Precise direct-write lithography of 3D waveguides or diffractive structures within the volume of a photosensitive material is hindered by the lack of metrology that can yield predictive models for the micron-scale refractive index profile in response to a range of exposure conditions. We apply the transport of intensity equation in conjunction with confocal reflection microscopy to capture the complete spatial frequency spectrum of isolated 10 μm-scale gradient-refractive index structures written by single-photon direct-write laser lithography. The model material, a high-performance two-component photopolymer, is found to be linear, integrating, and described by a single master dose response function. The sharp saturation of this function is used to demonstrate nearly binary, flat-topped waveguide profiles in response to a Gaussian focus.

Understanding and Improving Mechanical Properties in 3D printed Parts Using a Dual‐Cure Acrylate‐Based Resin for Stereolithography

“…The exposure time was varied for a constant intensity and the cure depth measured using a confocal reflection microscope for optical profilometry. [24] Figure 3e shows the mean cure depth as function of incident exposure E 0 .…”

“…Seven samples were fabricated to investigate the effect of exposure conditions on cure depth by varying exposure times (4, 6, 12, 18, 24, 48, and 96 s) ( n = 3/group). The samples were soaked in ethanol for 72 h. The Cure depth was measured through the use of a custom-built optical profilometer as described by Glugla et al [24] …”

Spatial modulation of scalable nanostructures by combining maskless plasmonic lithography and grayscale-patterned strategy

“…[6][7][8][9][10][11] Thus far, the mainstream approaches for accurate nanofabrication with arbitrary shapes are photolithography and laser direct write lithography. [12][13][14][15][16][17][18][19][20][21][22] Photolithography can provide large scale patterning, and laser direct write lithography has shown its great potential in the fabrication of complex three-dimensional micro-nano structures. However, they suffer from limited pattern resolution by the intrinsic property of light diffraction.…”

The optical refractometry using transport-of-intensity equation

“…Although optical methods of refractometry are still the main way to measure the refractive index [1], other approaches have been developed to solve this problem [2][3][4][5][6][7][8]. Among them, the methods based on the application of the transport-of-intensity equation (TIE) deserve special attention [9][10][11]. The main idea of these methods lies in the connection of the refractive index with the phase of the light wave that has passed through the optical medium.…”

“…Later, Yazdani et al [10] investigated the use of TIE to determine the nonlinear refractive index n 2 of a material. Finally, in 2018, Glugla et al [11] used the TIE to estimate the refractive index in 3D lithography. Note that the disadvantages of the proposed approaches are either the complex optical systems or the presence of additional time-consuming mathematical calculations.…”