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Computational Temporal Ghost Imaging Extends to Mid-Infrared

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CHENGDU, China, Aug. 27, 2024 — Ghost imaging in the time domain allows for reconstructing fast temporal objects using a slow photodetector. The technique involves correlating random or preprogrammed probing temporal intensity patterns with the integrated signal measured after modulation by the temporal object. However, the implementation of temporal ghost imaging necessitates ultrafast detectors or modulators for measuring or preprogramming the probing intensity patterns, which are not available in all spectral regions especially in the MIR region.

A team of scientists, led by Sichuan University professor Houkun Liang and professor Goëry Genty from Tampere University, have developed a frequency downconversion temporal ghost imaging (TGI) scheme that enables to extend the operation regime to arbitrary wavelengths regions where fast modulators and detectors are not available. The approach modulates a signal with temporal intensity patterns in the near-infrared and transfers the patterns to an idler via difference-frequency generation in a nonlinear crystal at a wavelength where the temporal object can be retrieved.

The absence of suitable instrumentation, such as ultrafast MIR electro-optic modulators for preprogramming temporal patterns at MIR light sources, has been a bottleneck in the direct implementation of computational TGI in the MIR.

In the proposed new scheme, instead of directly preprogramming temporal patterns at MIR wavelengths, preprogrammed temporal patterns are modulated at NIR wavelengths using a conventional telecom modulator and, subsequently, these modulated patterns are transferred to a MIR idler via difference-frequency generation using a temporally stable continuous-wave NIR pump light source.


The wide availability of tunable lasers in the NIR allows for flexible and versatile operation of the downconversion TGI scheme, enabling the extension of TGI to wavelength regimes where there is a lack of fast detectors and modulators.

As a proof-of-concept, the researchers demonstrated a computational temporal ghost imaging in the MIR with operating wavelength that can be tuned from 3.2 to 4.3 μm. The scheme is flexible and can be extended to other regimes.

According to the researchers, the results introduce new possibilities for scan-free pump-probe imaging and the study of ultrafast dynamics in spectral regions where ultrafast modulation or detection is challenging such as the MIR and THz regions. The team expects that it can also be applied in the spatial and spectral domains, which could open a new venue for single-pixel imaging and spectroscopy in the mid-infrared and THz regions

The research was published in Light: Science & Application (www.doi.org/10.1038/s41377-024-01426-0).

Published: August 2024
Glossary
infrared
Infrared (IR) refers to the region of the electromagnetic spectrum with wavelengths longer than those of visible light, but shorter than those of microwaves. The infrared spectrum spans wavelengths roughly between 700 nanometers (nm) and 1 millimeter (mm). It is divided into three main subcategories: Near-infrared (NIR): Wavelengths from approximately 700 nm to 1.4 micrometers (µm). Near-infrared light is often used in telecommunications, as well as in various imaging and sensing...
terahertz
Terahertz (THz) refers to a unit of frequency in the electromagnetic spectrum, denoting waves with frequencies between 0.1 and 10 terahertz. One terahertz is equivalent to one trillion hertz, or cycles per second. The terahertz frequency range falls between the microwave and infrared regions of the electromagnetic spectrum. Key points about terahertz include: Frequency range: The terahertz range spans from approximately 0.1 terahertz (100 gigahertz) to 10 terahertz. This corresponds to...
near-infrared
The shortest wavelengths of the infrared region, nominally 0.75 to 3 µm.
time domain
The time domain is a concept used in signal processing and analysis to describe signals in terms of their behavior over time. In the time domain, signals are represented as functions of time, showing how the amplitude of the signal changes at each moment. Time-domain analysis provides insights into the temporal characteristics of signals. Here are key points related to the time domain: Signal representation: In the time domain, a signal is represented as a function of time. This...
Research & TechnologyImagingmid-infraredMIRmid infraredinfraredterahertzTHznear-infraredLaserstunabledownconversionghost imagingtime domaintemporalSichuan UniversityTampere UniversityAsia-PacificEuropeLight: Science & Application

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