Spectrophotometer Asymmetric Grating-Array Alignment
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Solution Overview
Problem
Conventional spectrophotometers suffer from reduced accuracy due to light returning from the photodiode array to the diffraction grating and re-entering the photodiode array, causing non-linear absorbance measurements at specific wavelengths.
Innovation Solution
The spectrophotometer design includes a slit, diffraction grating, and photodiode array where the normal plane to the diffraction grating surface is not coincident with the normal plane to the photodiode array, preventing light from returning to the photodiode array after reflection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the normal plane to the diffraction grating is coincident with the normal plane to the photodiode array, then the optical path is simplified and alignment is easier, but light reflects from the photodiode array back to the diffraction grating and re-enters the photodiode array, causing measurement errors
Solution Approach 1:
The patent applies asymmetry by deliberately making the normal plane to the diffraction grating non-coincident with the normal plane to the photodiode array. This asymmetric angular relationship breaks the symmetry of light reflection paths, preventing reflected light from returning to the diffraction grating and re-entering the photodiode array, thus eliminating measurement errors while maintaining practical alignment feasibility.
2Length of moving object
If the photodiode array is positioned to receive diffracted light directly, then the optical path length is minimized, but stray light reflects off the photodiode array surface and re-enters the detector, creating false absorbance signals
Solution Approach 1:
The patent implements preliminary anti-action by pre-configuring the optical system with a specific angular relationship between the diffraction grating and photodiode array normal planes. This preliminary setup prevents stray light from returning to the detector before it can cause measurement errors, effectively counteracting the harmful reflection effect in advance.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration ensures high-accuracy spectroscopic measurements by preventing stray light from re-entering the photodiode array, resulting in accurate light intensity measurements across all wavelengths.
Implementation Method 1
a diffraction grating which wavelength-disperses an incident light passing through the slit
Implementation Method 2
a photodiode array including a plurality of light intensity measurement elements arranged in a direction of the wavelength dispersion by the diffraction grating
Data Source
AI summary
A spectrophotometer in which a normal plane to a diffraction grating is inclined with respect to an optical axis of an incident light passing through a slit, the normal plane to the diffraction grating passing through an intersection point between the optical axis of the incident light i and a grating surface of the diffraction grating. The diffraction grating and a photodiode array PDA are placed such that the photodiode array PDA is parallel to the normal plane to the diffraction grating and that a normal plane to the photodiode array PDA includes a line that is symmetrical to the optical axis of the incident light i about the normal plane to the diffraction grating.