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10 pages, 1147 KiB

Open AccessArticle

A Multidimensional Multiplexing Mode-Locked Laser Based on a Dual-Ring Integrative Structure for Tri-Comb Generation

by Ruitao Yang, Hao Sun, Haisu Lv, Jian Xu, Jinxuan Wu, Pengcheng Hu, Haijin Fu, Hongxing Yang and Jiubin Tan

Appl. Sci. 2020, 10(22), 8260; https://doi.org/10.3390/app10228260 - 21 Nov 2020

Cited by 14 | Viewed by 2305

Abstract

The tri-comb-based multi-heterodyne detection technique has been proven to be a powerful tool for precision metrology, e.g., laser ranging and spectroscopy. However, in existing tri-comb generation methods, it is difficult to provide a large and variable difference in tri-comb repetition rates. In this [...] Read more.

The tri-comb-based multi-heterodyne detection technique has been proven to be a powerful tool for precision metrology, e.g., laser ranging and spectroscopy. However, in existing tri-comb generation methods, it is difficult to provide a large and variable difference in tri-comb repetition rates. In this paper; we propose a multidimensional multiplexing mode-locked laser based on a dual-ring integrative structure. Combining the dimensions of sub-ring multiplexing and wavelength multiplexing, two modes of tri-comb generation can be achieved with the dual-ring single cavity laser. The generated combs are identified based on the relative intensity of the pulse trains and optical spectrum, and the repetition rates of dual-combs from the same sub-ring are distinguished based on dispersion analysis. With repetition rates of approximately 47 MHz and 49.6 MHz, the minimum and maximum repetition rate difference of the generated tri-comb can be changed from 2.38 kHz and 2.59526 MHz to 2.74 kHz and 2.59720 MHz merely by switching the operation mode of the dual-ring integrated mode-locked laser. The obtained results indicate that our method can offer a powerful scheme for future multi-comb generation and its application in multi-heterodyne detection-based laser ranging and spectroscopy. Full article

(This article belongs to the Special Issue Ultrafast Optics: Trends and Prospects)

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9 pages, 2085 KiB

Open AccessArticle

Real-Time Multidepth Multiphoton Microscopy Using Pixel-to-Pixel Focus-Switching

by Yifan Qin, Deying Chen and Yuanqin Xia

Appl. Sci. 2020, 10(20), 7173; https://doi.org/10.3390/app10207173 - 15 Oct 2020

Cited by 2 | Viewed by 2283

Abstract

Multiphoton microscopy is a well-established technique for biomedical applications, but real-time multidepth multimodal multiphoton microscopy using non-imaging detection has barely been discussed. We demonstrate a novel label-free imaging system capable of generating multimodal multiphoton signals at different focal planes simultaneously. Two spatially overlapped [...] Read more.

Multiphoton microscopy is a well-established technique for biomedical applications, but real-time multidepth multimodal multiphoton microscopy using non-imaging detection has barely been discussed. We demonstrate a novel label-free imaging system capable of generating multimodal multiphoton signals at different focal planes simultaneously. Two spatially overlapped and temporally interlaced beams are obtained by applying cost-effective electro-optic modulator (EOM)-based fast-switching light paths. The switching beams have different divergence properties, enabling imaging at different depths into samples. The EOM is synchronized to the pixel clock from the microscope, achieving pixel-to-pixel focus-switching. The capability of the imaging system is demonstrated by performing real-time multidepth two-photon fluorescence (TPF) and second-harmonic generation (SHG) imaging of freshly excised mouse lung lobes. TPF and SHG images are acquired at two wavelength ranges. One is between 415 and 455 nm, and the other is between 495 and 635 nm. The microenvironment of pulmonary alveoli is depicted by the distributions of both elastin fibers visualized by TPF and collagen fibers illustrated by SHG. Macrophages residing inside apparent alveolar lumens are also identified by TPF, which shows that the imaging system is capable of localizing biological objects in three dimensions and has the potential of monitoring in vivo cellular dynamics in the axial direction. Full article

(This article belongs to the Special Issue Ultrafast Optics: Trends and Prospects)

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14 pages, 19733 KiB

Open AccessArticle

Water Temperature and Salinity Measurement Using Frequency Comb

by Haoyun Zhang, Xinyang Xu, Haihan Zhao, Fanpeng Dong, Zhiwen Qian and Bin Xue

Appl. Sci. 2019, 9(23), 5043; https://doi.org/10.3390/app9235043 - 22 Nov 2019

Cited by 4 | Viewed by 2966

Abstract

Water temperature and salinity are key parameters in many fields such as industry, forestry and agriculture. In this paper, we, theoretically and experimentally, demonstrate a method which is capable of water temperature and salinity measurement based on a laser frequency comb at 518 [...] Read more.

Water temperature and salinity are key parameters in many fields such as industry, forestry and agriculture. In this paper, we, theoretically and experimentally, demonstrate a method which is capable of water temperature and salinity measurement based on a laser frequency comb at 518 nm. We have developed a simple Michelson interferometer system. By scanning a mirror on a precision displacement platform, a pair of cross-correlation patterns can be obtained. The real-time optical distance information from these cross-correlation patterns can be used to calculate the optical distance difference changes. Temperature and salinity can be measured via these changes, aided by the empirical formulas. Compared with the reference values, our results show the differences of below 0.12 °C for temperature measurements, and 0.06‰ for salinity measurements. The obtained results indicate that our method can offer a powerful scheme for future temperature and salinity measurement. Full article

(This article belongs to the Special Issue Ultrafast Optics: Trends and Prospects)

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17 pages, 14125 KiB

Open AccessArticle

Study on Femtosecond Laser Processing Characteristics of Nano-Crystalline CVD Diamond Coating

by Chao Wei, Yuping Ma, Yuan Han, Yao Zhang, Liu Yang and Xuehui Chen

Appl. Sci. 2019, 9(20), 4273; https://doi.org/10.3390/app9204273 - 12 Oct 2019

Cited by 14 | Viewed by 4264

Abstract

Ultra-short pulse laser interaction with diamond materials has attracted extensive interest in micro- and nano-machining, especially for the fabrication of micro tools, because of the straightforward method and high precision. Thanks to the development of chemical vapor deposition (CVD) technology, high-quality CVD diamonds [...] Read more.

Ultra-short pulse laser interaction with diamond materials has attracted extensive interest in micro- and nano-machining, especially for the fabrication of micro tools, because of the straightforward method and high precision. Thanks to the development of chemical vapor deposition (CVD) technology, high-quality CVD diamonds are employed in more varieties of tools as performance-enhancing coatings. The purpose of the experiments reported here was to explore the machinability of CVD diamond coating under the irradiation of femtosecond (fs) pulsed laser. The factor-control approach was adopted to investigate the influence of scanning speed, single pulse energy and repetition rate on the surface quality and carbon phase transition of CVD diamond coating. The material removal rate and surface roughness were evaluated. The interaction mechanism of scanning speed, single pulse energy, and repetition rate were discussed, and the fs laser ablation threshold of CVD diamond coating was calculated. It was demonstrated that two ablation mechanisms (weak and intensive) were in existence as evidenced by the distinct surface morphologies induced under different processing conditions. A strong dependence on the variation of scanning speed and pulse energy is identified in the examination of surface roughness and removal rate. Lorentzian–Gaussian deconvolution of Raman spectra illustrates that fs laser irradiation yields a strong modification effect on the coating and release the compressive stress in it. Furthermore, a newly defined parameter referring to the fs laser energies applied to unit volume was introduced to depict the degree of ablation and the Taguchi method was used to figure out the significance of different parameters. The ablation threshold of CVD diamond coating at the effective pulses of 90 is calculated to be 0.138 J/cm². Full article

(This article belongs to the Special Issue Ultrafast Optics: Trends and Prospects)

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10 pages, 3435 KiB

Open AccessArticle

Numerical Investigation on the Influence of Water Vapor Ionization on the Dynamic and Energy Deposition of Femtosecond Ultraviolet Laser Filamentation in Air

by Qingwei Zeng, Lei Liu, Kejin Zhang, Shuai Hu, Taichang Gao, Chensi Weng and Ming Chen

Appl. Sci. 2019, 9(20), 4201; https://doi.org/10.3390/app9204201 - 9 Oct 2019

Cited by 4 | Viewed by 2666

Abstract

The effects of water vapor ionization on the nonlinear propagation of femtosecond laser pulses with a 248 nm wavelength are numerically investigated in this paper. It is found that ionization of H₂O molecules plays a significant role in air ionization, which [...] Read more.

The effects of water vapor ionization on the nonlinear propagation of femtosecond laser pulses with a 248 nm wavelength are numerically investigated in this paper. It is found that ionization of H₂O molecules plays a significant role in air ionization, which seriously affects the dynamic and energy deposition of filamentation. The propagation of femtosecond pulses in air with different humidity levels are compared. The total number of electrons and total deposited pulse energy increase with the humidity increases. However, they tend to be saturated in high humidity conditions. Results presented here are conducive to characterizing the long-range propagation of filaments under atmospheric conditions. Full article

(This article belongs to the Special Issue Ultrafast Optics: Trends and Prospects)

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Review

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21 pages, 2047 KiB

Open AccessReview

Advanced Micro-Actuator/Robot Fabrication Using Ultrafast Laser Direct Writing and Its Remote Control

by Sangmo Koo

Appl. Sci. 2020, 10(23), 8563; https://doi.org/10.3390/app10238563 - 30 Nov 2020

Cited by 11 | Viewed by 4768

Abstract

Two-photon polymerization (TPP) based on the femtosecond laser (fs laser) direct writing technique in the realization of high-resolution three-dimensional (3D) shapes is spotlighted as a unique and promising processing technique. It is also interesting that TPP can be applied to various applications in [...] Read more.

Two-photon polymerization (TPP) based on the femtosecond laser (fs laser) direct writing technique in the realization of high-resolution three-dimensional (3D) shapes is spotlighted as a unique and promising processing technique. It is also interesting that TPP can be applied to various applications in not only optics, chemistry, physics, biomedical engineering, and microfluidics but also micro-robotics systems. Effort has been made to design innovative microscale actuators, and research on how to remotely manipulate actuators is also constantly being conducted. Various manipulation methods have been devised including the magnetic, optical, and acoustic control of microscale actuators, demonstrating the great potential for non-contact and non-invasive control. However, research related to the precise control of microscale actuators is still in the early stages, and in-depth research is needed for the efficient control and diversification of a range of applications. In the future, the combination of the fs laser-based fabrication technique for the precise fabrication of microscale actuators/robots and their manipulation can be established as a next-generation processing method by presenting the possibility of applications to various areas. Full article

(This article belongs to the Special Issue Ultrafast Optics: Trends and Prospects)

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12 pages, 8243 KiB

Open AccessReview

High-Quality, InN-Based, Saturable Absorbers for Ultrafast Laser Development

by Laura Monroy, Marco Jiménez-Rodríguez, Eva Monroy, Miguel González-Herráez and Fernando B. Naranjo

Appl. Sci. 2020, 10(21), 7832; https://doi.org/10.3390/app10217832 - 4 Nov 2020

Cited by 4 | Viewed by 2611

Abstract

New fabrication methods are strongly demanded for the development of thin-film saturable absorbers with improved optical properties (absorption band, modulation depth, nonlinear optical response). In this sense, we investigate the performance of indium nitride (InN) epitaxial layers with low residual carrier concentration (<10 [...] Read more.

New fabrication methods are strongly demanded for the development of thin-film saturable absorbers with improved optical properties (absorption band, modulation depth, nonlinear optical response). In this sense, we investigate the performance of indium nitride (InN) epitaxial layers with low residual carrier concentration (<10¹⁸ cm⁻³), which results in improved performance at telecom wavelengths (1560 nm). These materials have demonstrated a huge modulation depth of 23% and a saturation fluence of 830 µJ/cm², and a large saturable absorption around −3 × 10⁴ cm/GW has been observed, attaining an enhanced, nonlinear change in transmittance. We have studied the use of such InN layers as semiconductor saturable absorber mirrors (SESAMs) for an erbium (Er)-doped fiber laser to perform mode-locking generation at 1560 nm. We demonstrate highly stable, ultrashort (134 fs) pulses with an energy of up to 5.6 nJ. Full article

(This article belongs to the Special Issue Ultrafast Optics: Trends and Prospects)

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15 pages, 5044 KiB

Open AccessReview

The Development of the Temporal Measurements for Ultrashort Laser Pulses

by Yi Cai, Zhenkuan Chen, Xuanke Zeng, Huangcheng Shangguan, Xiaowei Lu, Qiying Song, Yuexia Ai, Shixiang Xu and Jingzhen Li

Appl. Sci. 2020, 10(21), 7401; https://doi.org/10.3390/app10217401 - 22 Oct 2020

Cited by 4 | Viewed by 3907

Abstract

In the past three decades, ultrafast pulse laser technology has greatly progressed and applied widely in many subjects, such as physics, chemistry, biology, materials, and so on. Accordingly, as well as for future developments, to measure or characterize the pulses temporally in femtosecond [...] Read more.

In the past three decades, ultrafast pulse laser technology has greatly progressed and applied widely in many subjects, such as physics, chemistry, biology, materials, and so on. Accordingly, as well as for future developments, to measure or characterize the pulses temporally in femtosecond domain is indispensable but still challenging. Based on the operation principles, the measurement techniques can be classified into three categories: correlation, spectrogram, and spectral interferometry, which operate in time-domain, time-frequency combination, and frequency-domain, respectively. Here, we present a mini-review for these techniques, including their operating principles, development status, characteristics, and challenges. Full article

(This article belongs to the Special Issue Ultrafast Optics: Trends and Prospects)

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