Continuous Spatial Tuning of Laser Emissions in a Full Visible Spectral Range

Mi-Yun Jeong,Jeong Weon Wu

doi:10.3390/ijms12032007

Abstract

In order to achieve a continuous tuning of laser emission, the authors designed and fabricated three types of cholesteric liquid crystal cells with pitch gradient, a wedge cell with positive slope, a wedge cell with negative slope, and a parallel cell. The length of the cholesteric liquid crystal pitch could be elongated up to 10 nm, allowing the lasing behavior of continuous or discontinuous spatial tuning determined by the boundary conditions of the cholesteric liquid crystal cell. In the wedge cell with positive slope, the authors demonstrated a continuous spatial laser tuning in the near full visible spectral range, with a tuning resolution less than 1 nm by pumping with only a single 355 nm laser beam. This continuous tuning behavior is due to the fact that the concentration of pitch gradient matches the fixed helical pitch determined by the cell thickness. This characteristic continuous spatial laser tuning could be confirmed again by pumping with a 532 nm laser beam, over 90 nm in the visible spectral range. The scheme of the spatial laser tuning in the wedge cell bearing a pitch gradient enabled a route to designing small-sized optical devices that allow for a wide tunability of single-mode laser emissions.

Highlights

IntroductionP. Il’chishin et al [1] first reported the lasing operation in dye-doped cholesteric liquid crystals (CLC), as a one-dimensional photonic crystal laser system, their subsequent and increased study has yielded much useful data [2,3,4,5,6]
When the concentration of pitch gradient fits with the helical pitch determined by the cell thickness with positive slope, Cano lines disappear, which is similar to the wedge cell with positive slope, (Figure 2b,d,f)
In order to study the mechanism of the continuous laser tuning in cholesteric liquid crystals (CLC) cells, the authors designed and fabricated three types of cholesteric liquid crystal cells, a wedge cell with a positive slope, a wedge cell with a negative slope, and a parallel cell, and found that the length of the pitch length could be elongated up to 10 nm, and the behavior of continuous or discontinuous laser tuning is determined by the boundary conditions of the CLC cells

Summary

Introduction

P. Il’chishin et al [1] first reported the lasing operation in dye-doped cholesteric liquid crystals (CLC), as a one-dimensional photonic crystal laser system, their subsequent and increased study has yielded much useful data [2,3,4,5,6]. The authors demonstrated a continuous spatial laser tuning, with a tuning resolution less than 1 nm in the broad visible spectral range, by implementing a gradual change in the optical helical pitch in the wedge cell structure [21]. Repeating of the lasing experiment on other wedge cells with different CLCs by pumping with a 532 nm laser beam yielded the same lasing behavior, with a continuous spatial tuning in the spectral range over 90nm in the visible spectra. Further study of the continuous laser tuning mechanism in the wedge cell with three types of cholesteric liquid crystal cells revealed that the length of the pitch length could be elongated up to 10 nm, and the behavior of the continuous or discontinuous laser tuning could be determined by the boundary conditions within the CLC cells

Experimental Section Sample Preparation

Results and Discussion

Conclusions