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Photonics
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Ultrafast Optics: From Fundamental Science to Applications
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Ultrafast Optics: From Fundamental Science to Applications

A special issue of Photonics (ISSN 2304-6732).

Deadline for manuscript submissions: closed (28 February 2026) | Viewed by 5204

Special Issue Editor

Dr. Bo Fu

E-Mail Website
Guest Editor
School of Instrumentation and Optoelectronic Engineering, Beihang University, Beijing 100191, China
Interests: ultrafast lasers; optical frequency combs; nanophotonics; laser photonics
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Ultrafast optics provide a key observation method for revealing the transient dynamic behavior of photons. Boasting extreme temporal manipulation capabilities, multidimensional spatiotemporal modulation, and ultrahigh measurement precision, ultrafast optics demonstrates immense application potential in optical communication, environmental monitoring, spectroscopy, material processing, biomedicine, and other fields.

In an era marked by groundbreaking advancements in photonics, ultrafast optics stands at the forefront of transformative technology, poised to redefine both scientific inquiry and practical innovation. Currently, further research is essential to advance both the fundamental science and practical applications of ultrafast optics. For fundamental science, it is imperative to systematically investigate the nonlinear dynamic evolution mechanisms in pulsed laser systems. Meanwhile, the regulatory mechanisms of how metasurfaces act on optical fields to achieve on-demand dynamic control of optical field characteristics also need to be explored. In terms of applications, enabled by these characteristics, ultrafast lasers are adopted in different technologies, each of which presents its own challenges. For example, optical frequency combs have important application value in the field of spectroscopy due to their excellent time domain and frequency domain characteristics. However, conventional optical frequency combs require bulky laser architectures that impose fundamental limitations on cost, power efficiency, and system integration, necessitating the development of chip-scale microcavity optical frequency combs with compact nonlinear photonic engineering.

This Special Issue aims to present an informative and inspiring collection of articles on fundamental science and applications in ultrafast optics. Research reports and reviews are both welcomed, and researchers are invited to submit their contributions to this Special Issue on topics that include, but are not limited to, the following:

  • Ultrafast photonics;
  • Laser photonics;
  • Nanophotonics;
  • Metasurface optics;
  • Fiber optics;
  • Nonlinear dynamics;
  • On-chip microcavity;
  • Optical frequency combs;
  • Laser absorption spectroscopy.

Dr. Bo Fu
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 250 words) can be sent to the Editorial Office for assessment.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Photonics is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • ultrafast photonics
  • laser photonics
  • nanophotonics
  • metasurface optics
  • fiber optics
  • nonlinear dynamics
  • on-chip microcavity
  • optical frequency combs
  • laser absorption spectroscopy

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Published Papers (5 papers)

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Research

23 pages, 3391 KB  
Article
Simulating Cascaded Harmonics Generation up to the Sixth Order in β-BBO
by Jozsef Seres, Enikoe Seres and Thorsten Schumm
Photonics 2026, 13(5), 436; https://doi.org/10.3390/photonics13050436 - 29 Apr 2026
Viewed by 201
Abstract
We simulate the generation of multiple harmonics up to the sixth order extending into vacuum ultraviolet. The harmonics are generated by χ(n):χ(m) cascades, containing second- or third-order perturbative nonlinear processes. We identify three additional phase-matching conditions beyond standard phase matching, [...] Read more.
We simulate the generation of multiple harmonics up to the sixth order extending into vacuum ultraviolet. The harmonics are generated by χ(n):χ(m) cascades, containing second- or third-order perturbative nonlinear processes. We identify three additional phase-matching conditions beyond standard phase matching, namely when only the first step or only the second step of the cascades are phase-matched and when the non-phase-matched second or third harmonic produces quasi-phase matching for higher-order harmonics, causing an essential enhancement of the harmonic signals. Full article
(This article belongs to the Special Issue Ultrafast Optics: From Fundamental Science to Applications)
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12 pages, 1157 KB  
Article
Accuracy and Validity Range of a Simplified Lorentzian Approximation for Pressure-Broadened 87Rb Hyperfine Spectra
by Shangtao Jiang, Tengyue Wang, Xuyang Qiu and Heng Yuan
Photonics 2026, 13(3), 221; https://doi.org/10.3390/photonics13030221 - 26 Feb 2026
Viewed by 454
Abstract
Reliable modeling of pressure-broadened spectra is essential for maintaining physical consistency in alkali vapor-cell diagnostics. In this work, we investigate the low-power absorption spectra of isotopically enriched 87Rb vapor cells at the D1 and D2 transitions, systematically comparing three fitting [...] Read more.
Reliable modeling of pressure-broadened spectra is essential for maintaining physical consistency in alkali vapor-cell diagnostics. In this work, we investigate the low-power absorption spectra of isotopically enriched 87Rb vapor cells at the D1 and D2 transitions, systematically comparing three fitting algorithms: single Lorentzian, hyperfine-resolved Voigt, and the doublet Lorentzian approximation. Experiments were performed across optical intensities from 40 nW to 10 mW, buffer-gas pressures from 200 Torr to 520 Torr, and temperatures between 370 K and 390 K. It is shown that when the pressure broadening dominates over Doppler broadening and the optical intensity remains below the saturation regime, the reduced doublet Lorentzian model achieves a fitting accuracy of R2 > 0.996. Under the pressure conditions of 350 Torr, the fitting error for both the doublet and Voigt approximations remains below 0.3% for the D2 line and below 0.1% for the D1 line. At the pressures of 520 Torr and under elevated optical intensities, the spectrum evolves toward a single-peaked profile, rendering a single Lorentzian model sufficient. The quantitative applicability boundary of the doublet approximation in 87Rb vapor cells is established, defining the operational regime where hyperfine-resolved modeling can be reduced under collision-dominated conditions in NMRG systems. Full article
(This article belongs to the Special Issue Ultrafast Optics: From Fundamental Science to Applications)
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18 pages, 5438 KB  
Article
Ultrafast NIR kHz and GHz Burst Laser Micro-Structuring of Polyimide Films
by Shuai Wang, Chiara Mischo, Walter Perrie, Jose Rajendran, Amin Ibrahim, Yin Tang, Patricia Scully, Dave Atkinson, Yue Tang, Matthew Bilton, Richard Potter, Laura Corner, Geoff Dearden and Stuart Edwardson
Photonics 2026, 13(2), 179; https://doi.org/10.3390/photonics13020179 - 11 Feb 2026
Viewed by 632
Abstract
An ultrafast laser system combined with an optical delay line allowed ablation and in-scription at 1 kHz and 1 GHz pulse burst within transparent polyimide films. The two-photon-induced absorption results in clean surface ablation, while inscription results in polymer decomposition, creating carbonised regions [...] Read more.
An ultrafast laser system combined with an optical delay line allowed ablation and in-scription at 1 kHz and 1 GHz pulse burst within transparent polyimide films. The two-photon-induced absorption results in clean surface ablation, while inscription results in polymer decomposition, creating carbonised regions within the polymer. Three pulse bursts at 1 GHz increased the observed coupling to the material significantly. Modified regions (with linewidths down to a few microns) were investigated using optical microscopy, white light interferometry, SEM and Raman spectroscopy, supporting the increasing carbon density relative to the pristine polymer. As depth of field was only a few microns at high NA, 3D micro-structuring was achieved. Polymer decomposition produces gaseous products, resulting in internal stress and thus affecting inscription fidelity. An inscribed subsurface electrode with dimensions of 5 mm × 0.3 mm × 3 μm connected to conducting vias had a resistance of R = 10.6 ± 0.2 kΩ, along with resistivity of ρ ~ 0.19 Ω cm; hence, it had DC conductivity, σ ~ 5.3 Scm−1. This conductivity is similar to that of bulk graphite and could well form the basis of future flexible sensors, demonstrating single-step 3D subsurface inscription of carbon or laser-induced graphene structures. Full article
(This article belongs to the Special Issue Ultrafast Optics: From Fundamental Science to Applications)
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11 pages, 2284 KB  
Article
Pulse Shaping in Hybrid Waveguides with the High-Order Kerr Nonlinearity
by Yuke Zhai, Lijuan Xu, Yuan Li and Lin Zhang
Photonics 2025, 12(11), 1103; https://doi.org/10.3390/photonics12111103 - 9 Nov 2025
Viewed by 752
Abstract
Kerr nonlinear effect extremely impacts both the spectral and the temporal evolutions of ultrashort pulses, although it is challenging to tailor over a broadened spectral region. In this work, we propose an on-chip Si3N4-organic hybrid waveguide with sophisticated non-monotonic [...] Read more.
Kerr nonlinear effect extremely impacts both the spectral and the temporal evolutions of ultrashort pulses, although it is challenging to tailor over a broadened spectral region. In this work, we propose an on-chip Si3N4-organic hybrid waveguide with sophisticated non-monotonic nonlinear coefficient γ(ω). A chirp-free pulse can be broadened or compressed at different peak powers in the normal dispersion range. The impact of the second-order Kerr nonlinearity with respect to frequency can overbalance that of dispersion. This new method deepens the understanding of the high-order nonlinear effects and help exploit innovative nonlinearity-engineered on-chip platforms for pulse shaping in the immediate future. Full article
(This article belongs to the Special Issue Ultrafast Optics: From Fundamental Science to Applications)
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15 pages, 6035 KB  
Article
Machine Learning-Assisted Optimization of Femtosecond Laser-Induced Superhydrophobic Microstructure Processing
by Lifei Wang, Yucheng Gu, Xiaoqing Tian, Jun Wang, Yan Jia, Junjie Xu, Zhen Zhang, Shiying Liu and Shuo Liu
Photonics 2025, 12(6), 530; https://doi.org/10.3390/photonics12060530 - 23 May 2025
Cited by 2 | Viewed by 2458
Abstract
Superhydrophobic surfaces have garnered significant attention due to their pivotal roles in various fields. Femtosecond laser technology provides a feasible means for inducing superhydrophobic microstructures on material surfaces. However, due to the unclear influence mechanisms of process parameters, as well as the high [...] Read more.
Superhydrophobic surfaces have garnered significant attention due to their pivotal roles in various fields. Femtosecond laser technology provides a feasible means for inducing superhydrophobic microstructures on material surfaces. However, due to the unclear influence mechanisms of process parameters, as well as the high cost and time-consuming nature of experiments, identifying the optimal femtosecond laser processing parameters within the process space remains a significant challenge. To address this issue, a process optimization framework that couples machine learning and genetic algorithms was proposed and successfully applied to the optimization of femtosecond laser-induced groove structures on TC4 alloy surfaces. Firstly, based on 64 sets of experimental data, the effects of the power, scanning speed, and scanning interval on the micro-groove structures and their wetting properties were discussed in detail. Furthermore, by utilizing this small sample dataset, various machine learning algorithms were employed to establish a prediction model for the contact angle, among which support vector regression demonstrated the optimal predictive accuracy. Three additional dimensional variables, i.e., the number of effective pulses, energy deposition rate, and roughness, were also added to the original dataset vectors as extra dimensions to participate in and guide the model training process. The prediction model was further coupled into a genetic algorithm to achieve the quantitative design of femtosecond laser processing. Compared to the best hydrophobicity in the original dataset, the contact angle of the designed process was improved by 5.5%. The proposed method provides an ideal solution for accurately predicting wetting properties and identifying optimal processes, thereby accelerating the development and application of femtosecond laser-induced superhydrophobic microstructures. Full article
(This article belongs to the Special Issue Ultrafast Optics: From Fundamental Science to Applications)
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