Oblique Helicoidal Cholesteric Liquid Crystal Laser Tuning
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Solution Overview
Problem
Existing electrically tunable lasers using cholesteric liquid crystals face challenges in maintaining the sinusoidal distribution of the local refractive index when an electric field is applied, leading to reduced laser emission intensity due to director field distortions, limiting their wavelength tuning range and efficiency.
Innovation Solution
The development of an oblique helicoidal cholesteric liquid crystal structure with a small elastic constant of bend, where the electric field controls the pitch and conical angle without altering the sinusoidal refractive index distribution, allowing for broad spectral tuning of laser emission from ultraviolet to infrared.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If an electric field is applied to cholesteric liquid crystal to tune the lasing wavelength, then the wavelength tuning range is improved, but the sinusoidal distribution of the local refractive index is distorted leading to reduced laser emission intensity
Solution Approach 1:
The patent changes the elastic constant parameter of the liquid crystal material by using a mixture containing dimeric liquid crystal compounds. This parameter change allows the material to form an oblique helicoidal structure under electric field that maintains sinusoidal refractive index distribution while enabling broad wavelength tuning, thus resolving the contradiction between tuning range and emission intensity
Solution Approach 2:
The patent employs a composite liquid crystal material system consisting of dimeric liquid crystal compounds mixed with conventional cholesteric liquid crystals. This composite approach creates a material with tailored elastic properties that enable the oblique helicoidal phase to form under electric field while preserving the sinusoidal refractive index distribution necessary for high laser emission intensity across a broad wavelength range
2Reliability
If the elastic constant of bend is increased to maintain structural stability under electric field, then the director field distortion is reduced, but the ability to achieve broad spectral tuning is limited
Solution Approach 1:
The patent optimizes the bend elastic constant parameter to a specific low value through material composition selection. This parameter optimization enables the liquid crystal to achieve both structural stability in the oblique helicoidal phase and broad spectral tuning capability, as the reduced elastic constant allows greater flexibility in pitch and conical angle adjustment under electric field while maintaining phase stability
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 approach enables electrically tunable lasers with a wide wavelength tuning range, high optical efficiency, and low driving voltage, suitable for diverse applications such as laboratory-on-a-chip, medical diagnostics, and holography, while maintaining emission intensity across different spectrum regions.
Implementation Method 1
It exhibits a photonic bandgap with a low-energy band edge at A and a high-energy edge at λh, determined by the pitch and effective refractive indices of the structure for differently polarized electromagnetic waves
Implementation Method 2
Photon emission by excited atoms and molecules and distributed feedback lasing is expected at the band edges
Implementation Method 3
The electric field controls the pitch P and the conical angle θ of the structure, but does not change the sinusoidal distribution of the local refractive index
Implementation Method 4
Disclosed herein are electrically tunable lasing devices using a structure of cholesteric liquid crystal, representing an oblique helicoid
Implementation Method 5
A pump laser 20 of a suitable wavelength, such as a Nd:YAG laser, generates a pump beam 22 that excites the laser to generate lasing light 24
Implementation Method 6
Photon emission by excited atoms and molecules and distributed feedback lasing is expected at the band edges
Data Source
AI summary
A lasing device includes an active layer comprising a cholesteric liquid crystal material and a laser dye, and a liquid crystal cell including spaced apart substrates defining a cell gap in which the active layer is disposed. The substrates include electrodes arranged to bias the active layer into an oblique helicoidal (ChOH) state. At least one substrate of the liquid crystal cell is optically transparent for a lasing wavelength range of the device.