Narrow-band Light Research Articles

Predicting melatonin suppression by light in humans: Unifying photoreceptor-based equivalent daylight illuminances, spectral composition, timing and duration of light exposure.

Light‐induced melatonin suppression data from 29 peer‐reviewed publications was analysed by means of a machine‐learning approach to establish which light exposure characteristics (ie photopic illuminance, five α‐opic equivalent daylight illuminances [EDIs], duration and timing of the light exposure, and the dichotomous variables pharmacological pupil dilation and narrowband light source) are the main determinants of melatonin suppression. Melatonin suppression in the data set was dominated by four light exposure characteristics: (1) melanopic EDI, (2) light exposure duration, (3) pupil dilation and (4) S‐cone‐opic EDI. A logistic model was used to evaluate the influence of each of these parameters on the melatonin suppression response. The final logistic model was only based on the first three parameters, since melanopic EDI was the best single (photoreceptor) predictor that was only outperformed by S‐cone‐opic EDI for (photopic) illuminances below 21 lux. This confirms and extends findings on the importance of the metric melanopic EDI for predicting biological effects of light in integrative (human‐centric) lighting applications. The model provides initial and general guidance to lighting practitioners on how to combine spectrum, duration and amount of light exposure when controlling non‐visual responses to light, especially melatonin suppression. The model is a starting tool for developing hypotheses on photoreceptors’ contributions to light's non‐visual responses and helps identifying areas where more data are needed, like on the S‐cone contribution at low illuminances.

Spectral dependency of the human pupillary light reflex. Influences of pre-adaptation and chronotype.

Non-visual photoreceptors (ipRGCs) and rods both exert a strong influence on the human pupil, yet pupil models regularly use cone-derived sensitivity as their basis. This inconsistency is further exacerbated by the fact that circadian effects can modulate the wavelength sensitivity. We assessed the pupillary reaction to narrowband light stimuli in the mesopic range. Pupil size for eighty-three healthy participants with normal color vision was measured in nine experimental protocols with varying series of continuous or discontinuous light stimuli under Ganzfeld conditions, presented after 90 seconds of dark adaptation. One hundred and fifty series of stimulation were conducted across three experiments, and were analyzed for wavelength-dependency on the normalized pupillary constriction (nPC), conditional on experimental settings and individual traits. Traits were surveyed by questionnaire; color vision was tested by Ishihara plates or the Lanthony D15 test. Data were analyzed with generalized additive mixed models (GAMM). The normalized pupillary constriction response is consistent with L+M-cone derived sensitivity when the series of light stimuli is continuous, i.e., is not interrupted by periods of darkness, but not otherwise. The results also show that a mesopic illuminance weighing led to an overall best prediction of pupillary constriction compared to other types of illuminance measures. IpRGC influence on nPC is not readily apparent from the results. When we explored the interaction of chronotype and time of day on the wavelength dependency, differences consistent with ipRGC influence became apparent. The models indicate that subjects of differing chronotype show a heightened or lowered sensitivity to short wavelengths, depending on their time of preference. IpRGC influence is also seen in the post-illumination pupil reflex if the prior light-stimulus duration is one second. However, shorter wavelengths than expected become more important if the light-stimulus duration is fifteen or thirty seconds. The influence of sex on nPC was present, but showed no interaction with wavelength. Our results help to define the conditions, under which the different wavelength sensitivities in the literature hold up for narrowband light settings. The chronotype effect might signify a mechanism for strengthening the individual´s chronotype. It could also be the result of the participant’s prior exposure to light (light history). Our explorative findings for this effect demand replication in a controlled study.

Recent advances on perfect light absorbers and their promise for high-performance opto-electronic devices [Invited

Perfect absorbers (PAs) are devices that can efficiently absorb electromagnetic waves. Great attention has been attracted since metamaterial PAs (MPAs) were first proposed in 2008. In recent years, with the development of nanophotonics and the improvement of nanomanufacturing technology, considerable progresses have been achieved in designing MPAs using new materials and new structures. In this review, we summarized first the latest developments of PAs from five directions: dual-band, multi-band, wideband, narrow-band, and tunable light absorption. The shortcomings of the previous PAs and the latest improvements were introduced as well. Then, the application of perfect absorption in solar cells, sensors, switches, and structural colors was discussed. Finally, we presented the main challenges and prospects in these fields. Novel PAs for applications in a wide field of opto-electronic devices will continuously progress with breakthrough advances in absorbers related technology and science.

Particle Size Measurement of Extinction Spectrum Based on Near-Infrared Narrow Band Light Source

Particle Size Measurement of Extinction Spectrum Based on Near-Infrared Narrow Band Light Source

Application of ESCO phytosystem based on narrow-band light-emitting diodes for growing cucumbers under photoculture conditions

The article deals with the study of photomorphogenesis of different cucumber varieties under light culture conditions. Studies were carried out under laboratory conditions using an experimental phytosystem ESCO based on narrow-band light-emitting diodes, which is equipped with a microcontroller. The microcontroller controls the supplementary light modes. Studies were conducted to develop recommendations for selecting and controlling the spectral composition of light optimal for the life cycle of plants. The aim of our research is to study photomorphogenesis of different cucumber varieties under light-culture conditions using an experimental ESCO phytosystem based on narrow-band light-emitting diodes equipped with a microcontroller that controls the supplementary light modes. Four cucumber hybrids were used to test the ESCO phytosystem. Phytolamps were placed at the height of 1 m in the beginning, then at the height of 1.2 m. Every day we recorded the growth of shoot length, establishment of generative organs (flowers), we recorded the date of flowering and fruit formation. Conditions of humidity, nutrient and air regimes corresponded to biological requirements of growth and development of cucumber plants. Studies have shown that laying of generative organs of cucumber with additional lighting with narrow-band light emitting diodes is good. Female flowers appeared 7-14 days earlier in BV700+RV350+ BF350+FRF350 regime than in plants grown under natural light. The RV light regime had a significant effect on the increase in plant height. Determination of chlorophyll content showed its optimal amount and depended on the varietal characteristics of plants. The best supplementary light mode was BV700+RV350+ BF350+FRF350 during the cultivation of seedlings of different cucumber hybrids. Mode change all to 500 after planting in the ground.

Defect-Induced Narrowband Light Emission from a 2D Hybrid Lead Iodide Perovskite

Defect-Induced Narrowband Light Emission from a 2D Hybrid Lead Iodide Perovskite

“Emmetropic, but not myopic human eyes distinguish positive defocus from calculated defocus in monochromatic red light”

Studies in animal models have provided evidence that broadband light and chromatic cues are necessary for successful emmetropization. We have studied this question in young human subjects by measuring short-term changes in axial length when they watched movies with calculated defocus (2.5D) or optically defocused movies (+2.5D) with red interference filters (620 ± 10 nm). Since filters cut luminance down by a factor of 10, a control experiment with neutral density filters (ND 1.0) was done. Ten myopes and 10 emmetropes were studied. Four experimental conditions were tested on two separate days. On the first day, movies with calculated defocus, and defocused by positive lenses were watched with ND filters. On the second day, movies with the same defocus patterns were watched with the red filters. Movies were presented on a large TV screen (LG OLED65C9, 65″) in a dark room at 2 m distance for 30 min. Changes in axial length before and after each stimulation were measured with the Lenstar (LS 900, with autopositioning system; Haag-Streit). Interestingly, the effects of calculated defocus or optical positive defocus on axial length were suppressed by 1.0 ND filters in myopes and emmetropes, with no clear trend. In contrast, narrow-band red light suppressed eye elongation with calculated defocus but not eye shortening with positive defocus in emmetropes. In myopes, as previously found in white light, there was a trend of axial eye elongation with positive lenses. In conclusion, the effect of positive lenses on eye growth did not require chromatic cues.

Method to Obtain LED Spectrum Optimizing Protection Effect and Color Quality for Lighting Dyed Cultural Relics Painted With Inorganic Pigments

Spectral radiation could cause color damage to dyed cultural relics, and finding a method to obtain a minimum-damage light source is a key issue to be solved. In this paper, the color change behavior of pigments under exposure was experimentally investigated by irradiating 17 typical inorganic pigments used for dyed cultural relics with 10 different narrow-band LED light sources. Through an analysis of the color difference of the test pigments against the amount of exposure, the responsivity equations of the pigments were obtained and a mathematical model for predicting the color damage degree was proposed. The 10 kinds of narrow-band light were combined to obtain 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> LED by using the exhaustive method. The Ra, R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">9</sub> , and | Duv | value of the above spectra were calculated. Ra≥90, R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">9</sub> ≥0, and | Duv | ≤0.0054 were taken as the evaluation basis, and 35,398 spectra that met color rendering requirements were obtained. The established mathematical model was used to calculate the color damage value to find the minimum-damage spectrum, which was then input into a Thouslite LEDCube system for reduction. An experiment was conducted among the minimum-damage LED and 3 randomly selected light sources, and results showed that the minimum-damage LED light source has an obvious illumination protection effect.

Role of Narrow Band Imaging in Laryngeal Lesions: A Prospective Study from Southern India.

To assess the utility of Narrow Band Imaging (NBI) as a diagnostic tool in evaluating laryngeal pathology in patients presenting with hoarseness. Study design: Prospective cross sectional diagnostic study. Methods: 200 patients with voice change were recruited and laryngeal findings documented with high definition flexible endoscopy with both white light and narrow band light and the representative still images recorded for analysis. The NBI intraepithelial papillary capillary loop (IPCL) patterns was compared with the histopathology report. Of the 200 patients evaluated, 84 lesions were biopsied which included both benign and malignant lesions. The sensitivity obtained was 73.3% [54.1-87.7% with 95% CI] and the specificity was 87% [75.1-94.6% with 95% CI] for detecting malignant lesions. NBI can be considered as a useful diagnostic tool in evaluating laryngeal pathology and can be used to detect early premalignant and malignant lesions.

Simulation of SSI-LED Light Emission Pattern Using Python As a Simulation Framework

A novel optoelectronic device named Solid-State Incandescent LED (SSI-LED) was reported by Kuo's group [1]. Intended to supplant conventional pn-junction LEDs in scenarios requiring ease of fabrication and compatible with Si technology, this device is made from a MOS capacitor with a high-k gate dielectric layer undergoing dielectric breakdown to form a large number of nano-sized conduction paths called Nano-resistors (NRs) [2]. Each NR has a small cross section, e.g., 10 nm diameter, and a high electrical resistance. When a voltage is applied across the device, these structures undergo incandescence, behaving similar to filaments in incandescent bulbs. As a result of thermal excitation, a broad and continuous spectrum of light is emitted, as opposed to narrow band lights from LEDs.Previous simulations of the device using COMSOL were limited by both the number of NRs that could be generated and the sizes of these NRs [3]. SEM images indicate that the SSI-LED should have at least a few hundred NRs per 30 μ2 [4]. In addition, simulation studies have shown that for certain devices, there is a higher density of NRs along the gate circumference [5].In order to extend both the functionality and flexibility of the current simulation to match the above requirements, a framework for SSI-LED geometry generation was made using Python. The current implementation can directly translate both a NR size in tabular format, and a position distribution in the form of concentric bands of limits expressed as rational multiples of the gate diameter, into built geometry within COMSOL. SEM images have also shown that NRs tend to form as aggregated clusters [4], which in the accompanying data were recorded as single large size light dots. In light of this, the code also can generate NRs in clusters by specifying the minimum and maximum 1) spread of clustered, 2) the number of NRs present in each cluster, and 3) the unique size distribution for clustered NRs. The program has the capability of having NRs generated both randomly as singular entities and as clusters in a simple percentage ratio. Additional parameters for finer control include a value to control the minimum space between random NRs and a clearance from the gate circumference edge.The python code removes the limit on number and sizes of NRs in the early light intensity simulations using MATLAB [3]. It extends utility into generating light intensity distribution data for the same geometry used in COMSOL, allowing for a one-to-one correspondence with the simulation model, and takes a number of steps to optimize the calculations for larger numbers of NRs and larger dot sizes.The output is stored as a file and accessed by a COMSOL-MATLAB Livelink, where it is possible to browse to any model through the Livelink interface and update the geometry of any COMSOL simulation model. This allows an already completed simulation model to be updated with the new geometry without having to redevelop the physics and post processing data contained in the simulation file.Figure 1 shows the light emitting patterns of a) a fabricated SSI-LED [6] and b) output from this simulation work, for comparison.[1] Y. Kuo and C.-C. Lin, Appl. Phys. Lett., 102, 031117 (2013).[2] Y. Kuo, IEDM, 4.7.1-4.7.4 (2014).[3] A. Shukla and Y. Kuo, ECS J. Solid State Sci. Technol., 9, 065017 (2020).[4] S. Zhang and Y. Kuo, J. Phys. D: Appl. Phys., 51, 09LT02 (2018).[5] K. Natarajan and Y. Kuo, to be published.[6] S. Zhang and Y. Kuo, ECS Trans., 85(3) 53-58 (2018). Figure 1

High-sensitivity FEES\xae with the professional image enhancement technology \u201cPIET\u201d

PurposeFlexible endoscopic evaluation of swallowing (FEES®) is a standard diagnostic tool in dysphagia. The combination of FEES® and narrow band light (narrow band imaging; NBI) provides a more precise and detailed investigation method. So far, this technique could only be performed with the NBI illumination. The new version of the “professional image enhancement technique” (PIET) provides another image enhancing system. This study investigates the eligibility of PIET in the FEES® procedure.MethodsBoth techniques, NBI and PIET, were compared using a target system. Furthermore, the image enhancement during FEES® was performed and recorded with the two systems during daily routine.ResultsPerforming an image enhancement during FEES® is possible with both systems PIET and NBI. On the target system, the contrast of the PIET showed a brighter and a more detailed picture. In dysphagia patients, no difference between PIET and NBI was detected.ConclusionsPIET proved to be non-inferior to NBI during image enhancement FEES®. So far, image enhancement FEES® was exclusively connected to NBI. With the PIET system, an alternative endoscopy technology is available for certain indications.

Tunable Resonant‐Photopyroelectric Detector Using Chalcogenide−Metal−Fluoropolymer Nanograting

AbstractPyroelectric detectors are often broadband and require external filters for wavelength‐specific applications. This paper reports a tunable, narrowband, and lightweight pyroelectric infrared detector built upon a flexible membrane of As2S3−Ag−P(VDF‐TrFE) with subwavelength grating, which is capable of both on‐chip filtering and photopyroelectric energy conversion. The top surface of this hybrid membrane is a corrugated As2S3−Ag film contributing to narrowband light absorption in the near‐infrared (NIR) regime, and the bottom part is a polyvinylidene fluoride‐trifluoroethylene (PVDF‐TrFE) membrane for the conversion of the absorbed light to an electrical signal. Uniquely, applying a bias voltage to the PVDF‐TrFE membrane enables the tuning of the device's absorption and pyroelectric characteristics owing to the piezoelectrically induced mechanical bending. The resonator exhibited a resonant absorption coefficient of 80% and a full‐width‐half‐maximum of 15 nm within the NIR, a responsivity of 1.4 mV mW−1, and an equivalent noise power of 13 µW Hz−1/2 at 1560 nm. By applying a 15‐V bias to the PVDF‐TrFE membrane, the absorption coefficient decreased to 18% due to the change in the grating period and incident angle. The narrowband and tunable features of the As2S3−Ag−P(VDF‐TrFE) pyroelectric detector will benefit a variety of potential applications in sensors, optical spectroscopy, and imaging.

Optimal LED spectrum for lighting Chinese paper cultural relics in museums

• Fourier transform infrared spectroscopy evaluated microscopic damage of paper. • Three-dimensional mathematical models and calculation formulas of lighting damage to paper. • The minimum-damage LED spectrum suitable for Chinese paper cultural relics. • The method of spectral optimization for the lighting source of cultural relics. In museum lighting, Chinese paper cultural relics are prone to cracking, embrittlement and other photochemical damage after absorbing the spectral energy of light sources. Owing to the different absorption and reflection characteristics of paper for different bands, optimizing the spectrum compositions of light sources can provide effective protection, the basis of which is to clarify the influence rule of spectra on the paper. However, the methods of color difference and Raman spectroscopy, which are widely used in the current research, cannot scientifically measure the lighting damage. In this study, Fourier transform infrared spectroscopy was used as the evaluation method, and 10 kinds of narrow-band lights were used as the experimental light source to conduct a 1440 h irradiation experiment on the samples of the ancient Chinese Xuan paper. The oxidation index was calculated as the evaluation index based on the infrared spectra measured every 240 hours, and a mathematical model for the response rate of paper to spectrum and exposure was established. 6 10 spectra were obtained with the 10 kinds of narrow-band lights combined and superimposed. The color rendering indexes of the above spectra were calculated, and 9,477 spectra that meet the requirements of viewing indicators were obtained. By calculating the damage degree of the above spectra with the model, the optimal LED spectrum with the minimum damage which met the visual requirements was obtained. Then it was input into the 10-channel spectral simulation system for spectral restoration. Two kinds of lights commonly used in lighting for paper cultural relics were selected to conduct a comparative experiment. The results showed that the optimal LED spectrum reduced damage degree by 49.4% and 59.7% respectively compared with the two kinds of contrast light sources, and was beneficial to energy saving.

Investigation of temperature effects of a 635 nm low power solid-state diode laser on agar phantom using two different thermocouples

It has been reported in the literature that low-level laser therapy is non-invasive, has no obvious side effects, has a very low cost, and is an effective and new treatment technique. It has been published that low-level laser therapy works at between 1 mW and 500 mW power, and between 390 nm and 1100 nm wavelengths without causing harmful heat to the human body, and in this technique, a high intensity, monochromatic, narrow-band light source is applied locally. It is also stated in this technique that instead of producing a thermal effect, photochemical reactions in the cells are stimulated, allowing the tissues to heal themselves. In this study, the temperature effects of a solid-state diode laser with a maximum operating power of 400 mW on the Agar phantom, which is an artificial tissue-mimicking material, were investigated using two different thermocouples for different distances and durations. In the study, Agar phantom as artificial tissue-mimicking material, red solid-state diode laser with 635 nm wavelength as a laser source, T-type ultra-thin thermocouple, and NTC type thermistor temperature sensor were used. The experiments were carried out separately for periods of 20 s, 40 s, 60 s, and 80 s time intervals. In this article, the results of temperature measurement studies both within the agar phantom by using two different thermocouples and two different temperature measurement systems, and on the surface of the agar phantom by using an infrared thermal camera were reported after realizing the characterization of the phantom. Besides, the laser used was also evaluated for the eye and skin contact within the concept of maximum permissible exposure (MEP).

Broadband ultrashort light generation from a narrowband seed

Light beams with broad spectral bandwidth are indispensable for the generation of ultrashort light pulses. Here, the generation of broadband ultrashort light pulses from narrowband seeds in transparent media is demonstrated. Broadband light pulses with a spectral width of hundreds of nanometers can be generated seeding with narrowband light pulses. The full spectral bandwidths of the narrowband seeds are several nanometers. Broadband ultrashort pulses from about 500 nm to 1020 nm are obtained seeding with a light beam at around 900 nm with 9 nm full spectral bandwidth. The temporal and spatial parameters of the generated broadband pulses are measured and analyzed. A new method for the generation of wavelength tunable broadband ultrashort lights is presented. The broadband light beam generation phenomenon can be explained by ping-pong four wave mixing (PPFWM) process, which helps us to understand all the optical parametric processes visually. The generated broadband pulses have potential applications in ultrafast spectroscopy and ultrafast pump–probe experiments.

Seed germination responses to low-level narrow-band light spectra for 14 ornamental plant genotypes

To investigate whether low-level lighting is necessary and which narrow-band light spectra are effective in seed germination, seeds of 14 genotypes from begonia (Begonia × tuberosa), echinacea (Echinacea spp.), gerbera (Gerbera jamesonii), petunia (Petunia × hybrida), and vinca (Catharanthus roseus) were germinated under ultraviolet-B (UVB), blue (B), green (G), red (R), far-red (FR) light, or darkness. Light-emitting diode (LED) fixtures provided all spectrum treatments except for UVB, which was provided by a narrow-band fluorescent light. The photon flux density at seed level was ≈18 μmol·m−2·s−1 for B, G, R, and FR, and 0.4 μmol·m−2·s−1 for UVB. Based on daily germination observations, final germination percentage, germination onset time, germination time spread, and germination speed were compared among different spectrum treatments for each of the plant genotypes. There were no promotive effects on final germination percentage, germination onset time, and germination time spread under the narrow-band lights compared with darkness. For all plant genotypes, B had a similar effect as darkness on seed germination. FR inhibited seed germination relative to darkness by reducing final germination percentage by 31%–88%, delaying germination onset time by 30%–40%, and decreasing germination speed by 11%–48% in some genotypes. Under R, G, and UVB compared with darkness, germination speed was promoted for begonia ‘Apricot Shade’, a light-requiring genotype, and inhibited for vinca ‘Burgundy’, a light-inhibited genotype. Therefore, lighting at low levels used in our study is unnecessary for seed germination of the tested species except light-requiring genotypes, where R, G, and UVB are the most promotive among the tested narrow-band lights.

Growth and morphological responses of gerbera seedlings to narrow-band lights with different light spectral combinations as sole-source lighting in a controlled environment

To optimize light-emitting diode (LED) spectral recipes for gerbera (Gerbera jamesonii) seedling propagation, seed germination and seedling morphology, biomass, flowering, and storage quality were observed in four cultivars, ‘Midi Dark Purple’, ‘Majorette Red Dark Eye’, ‘Maxi Pink’, and ‘Maxi White’, under six spectrum treatments: (1) FL, cool white fluorescent light; (2) RB, a photon flux ratio of 85% red and 15% blue (RB-LED); (3) RB + UVB, RB-LED combined with 0.5 μmol·m−2·s−1 of ultraviolet-B; (4) RB + UVA, RB-LED combined with 9.6 μmol·m−2·s−1 of ultraviolet-A; (5) RB + G, a photon flux ratio of 60% red, 15% blue, and 25% green; (6) RB + FR, RB-LED combined with 17.3 μmol·m−2·s−1 of far-red. For all treatments, the photosynthetic photon flux density was 165 μmol·m−2·s−1 under a 16-h photoperiod. Seedling growth and morphology were similar under FL and RB for all cultivars, except for a wider canopy of ‘Majorette Red Dark Eye’ under RB. Each of the tri-chromatic light treatments (i.e., RB + UVB, RB + UVA, RB + G or RB + FR) showed similar effects as RB, except for thicker ‘Maxi Pink’ stems under RB + FR. Furthermore, the quality index, an integrated evaluation of seedling quality, was similar under all the treatments for each cultivar. Given the similar seedling quality and the advantages of LEDs, RB-LED can potentially replace FL for controlled-environment gerbera seedling production, but the tri-chromatic lights tested in this study appear to be unnecessary.

27636 Addition of narrow-band ultraviolet light B phototherapy to ruxolitinib cream in patients with vitiligo

Previous reports with Janus kinase (JAK) inhibitors have suggested additional therapeutic benefit with concomitant phototherapy in patients with vitiligo. In a phase 2, randomized, dose-ranging study in adult patients with vitiligo (NCT03099304), ruxolitinib cream, a JAK1/JAK2 inhibitor, was associated with substantial repigmentation for up to 52 weeks of treatment as assessed by ≥50% improvement in facial and total Vitiligo Area Scoring Index (F-VASI50 and T-VASI50). After Week 52, patients were allowed to add narrow-band ultraviolet-B (NB-UVB) therapy while continuing open-label treatment with twice-daily 1.5% ruxolitinib cream.

Biological disease-modifying antirheumatic drugs may mitigate the risk of psoriatic arthritis in patients with chronic plaque psoriasis

ObjectiveTo estimate the incidence of psoriatic arthritis (PsA) in patients with psoriasis who had received a continuous treatment with biological disease-modifying antirheumatic drugs (bDMARDs) compared with phototherapy.MethodsA retrospective non-randomised study...

Tracking Ultrafast Structural Dynamics by Time-Domain Raman Spectroscopy.

In traditional Raman spectroscopy, narrow-band light is irradiated on a sample, and its inelastic scattering, i.e., Raman scattering, is detected. The energy difference between the Raman scattering and the incident light corresponds to the vibrational energy of the molecule, providing the Raman spectrum that contains rich information about the molecular-level properties of the materials. On the other hand, by using ultrashort optical pulses, it is possible to induce Raman-active coherent nuclear motion of the molecule and to observe the molecular vibration in real time. Moreover, this time-domain Raman measurement can be combined with femtosecond photoexcitation, triggering chemical changes, which enables tracking ultrafast structural dynamics in a form of “time-resolved” time-domain Raman spectroscopy, also known as time-resolved impulsive stimulated Raman spectroscopy. With the advent of stable, ultrashort laser pulse sources, time-resolved impulsive stimulated Raman spectroscopy now realizes high sensitivity and a wide detection frequency window from THz to 3000 cm–1, and has seen success in unveiling the molecular mechanisms underlying the efficient functions of complex molecular systems. In this Perspective, we overview the present status of time-domain Raman spectroscopy, particularly focusing on its application to the study of femtosecond structural dynamics. We first explain the principle and a brief history of time-domain Raman spectroscopy and then describe the apparatus and recent applications to the femtosecond dynamics of complex molecular systems, including proteins, molecular assemblies, and functional materials. We also discuss future directions for time-domain Raman spectroscopy, which has reached a status allowing a wide range of applications.