Proof-of-Principle Experiment of the Pseudorandom Multiplexing of White-Pump Light for Spectral Photothermal Microscopy

Absorption spectroscopy, coupled with photothermal super-resolution microscopy, is enabled by the frequency division multiplexing of the pump-light (Pu) wavelength whose spectral component is discriminated by the modulation frequency. This demonstrates a great advantage in availing multicolor image information. However, the response gain of the thermal lens signal to the spectral components is not uniform because of the limited relaxation rate of the thermal lens, i.e., the gains of the components assigned to the high-frequency modulations are diminished, thus resulting in a distorted absorption spectrum. In this study, white-pump light (Pu) is multiplexed by pseudonoise sequences (PNSs) to avoid the distortion. The frequency bandwidth of the PNSs is equalized, and the gains of the thermal lens generation to the respective wavelength components are balanced. The obtained results indicate that the modulation-waveform deformation due to the slow responses of the sample can also distort spectra. To mitigate the problem, the countermeasures required to compensate for this distortion are also discussed.     

Light Emitting Diodes Fabricated from Liquid Phase Epitaxial InAs/InAsxP1‐x‐ySby/InAsx'P1‐x'‐y'Sby' and InAs/InAs1‐xSbx Multi‐Layers

Mid‐infrared light emitting diodes (LED) in 3‐5μm wavelength range have been fabricated from InAs/InAs_xP_1‐x‐ySb_y/InAs_x'P_1‐x'‐y'Sb_y' composition graded layer and InAs/InAsSb multilayers. The heterostructures were grown by liquid phase epitaxy (LPE) between 600 and 520°C. An output power of 3.1 mW at 11K and of 10 μW at 300 K have been obtained under a peak current of 100 mA (50 % duty ratio) from InAsSb multilayers. Recombination mechanisms for these diodes were studied by temperature‐dependent emission spectra using Fourier transform infrared (FTIR) measurement system with double modulation. The output powers of the LEDs decrease rapidly at temperatures above 153 K suggesting that nonradiative and Auger recombinations are the main limitation of the device performance at high temperatures.