Pulsed Light Source Research Articles

Generation of a low divergent supercontinuum for mid-IR high power delivery through a large mode area photonic bandgap fiber

We numerically report the feasibility of generating broadband low divergent supercontinuum covering the entire wavelength window of 1.5–3.5 μm from a 2.25 m long effectively single mode all solid, soft glass based, photonic bandgap fiber with mode area as large as 1100 μm2. Owing to its chosen fabrication, friendly geometry, and the chosen material composition, the proposed fiber-based light source should be useful as a mid-wave IR pulsed broadband light source for applications such as high power delivery, optical coherence tomography and mid-IR spectroscopy.

Treatment of superficial vascular lesions with the KTP 532-nm laser: experience with 647 patients

Superficial vascular lesions are a common dermatological diagnosis but are often difficult to treat. Numerous lasers (especially the dye laser) and intense pulsed light sources have been used, but there have been very few reports on the effectiveness of the potassium-titanyl phosphate (KTP) laser. We have extensive experience of this modality at our institution, and the purpose of this survey is to report on the safety and efficacy of the KTP laser. Using an in-house database, we retrospectively collected data from patients who had undergone treatment with the KTP laser for superficial vascular lesions. Patients of Fitzpatrick skin type I-IV were included. Exclusion criteria were Fitzpatrick skin type V, patients with obvious suntan and those on potentially phototoxic medications or minocycline therapy. Diagnoses included discrete or matted telangiectasia, strawberry naevus, spider angioma, rosaceal erythema, rosaceal telangiectasia, telangiectatic naevus, angioma, combined rosaceal erythema/telangiectasia, port-wine stain, venous lake haemangioma and hereditary haemorrhagic telangiectasia. Patients underwent an initial test treatment and further treatment at 6-week intervals as required. Clinical photographs were taken pre- and post-treatment, and outcome was graded by patient and physician. Adverse effects were recorded including scarring, hypo- or hyperpigmentation, marked swelling, blistering, scabbing and bruising. Six hundred forty-seven patients with 13 diagnoses on 9 different body sites were recorded. Four hundred eighty-six were female, and the median age was 39.5years. Of the lesions treated, 33.7% (n = 218) were discrete telangiectases and 31.8% (n = 206) were spider angiomas. A 92.7% of lesions were on the face. Four hundred thirteen (77.6%) patients who had outcomes recorded at 6weeks were graded as "clearance" or "marked improvement". Only 38 (5.8%) patients experienced adverse effects, all of which were minor; the main adverse effect was swelling. Unlike the dye laser, there was only one case of bruising out of 647 patients. This is the largest survey of patients to have undergone KTP laser treatment reported in the literature. Our results show that the KTP laser is a safe and effective modality for the treatment of superficial vascular lesions.

Photoepilation with a diode laser vs. intense pulsed light: a randomized, intrapatient left-to-right trial

Safe and efficient options for removing unwanted hair are in great demand. Laser devices and intense pulsed light (IPL) sources are the most commonly used treatment modalities. Yet, only a few randomized controlled trials (RCTs) comparing laser and IPL devices are available, and RCTs with long-term results are missing from the literature. To compare the safety and long-term efficacy of diode lasers (DL) and IPL sources for axillary hair removal, we conducted an intrapatient, left-to-right, assessor-blinded and controlled trial. IPL (Ellipse Flex PPT; Danish Dermatological Development, Hoersholm, Denmark; λem=600-950 nm) and DL (LightSheer XC system; Lumenis Inc., Santa Clara, CA, U.S.A.; λem=800 nm) treatments were evaluated in 30 study participants (skin type II-III) with unwanted axillary hair growth. Six treatments with each device were carried out at 4-week intervals. Final assessment was conducted 12 months after the last treatment by means of hair counts using close-up photographs. The primary endpoint was reduction in hair growth, analysed on an intention-to-treat and last-observation-carried-forward basis (n=30), and secondary endpoints were patient-rated efficacy, treatment-related pain, adverse effects and treatment duration. Both devices significantly reduced hair counts. Mean reductions from baseline (3 and 12 months after the last treatment) were 59·7% and 69·2% for DL and 42·4% and 52·7% for IPL treatment (P<0·01), respectively. DL treatment induced significantly more pain [3·7±2·1 (DL) vs. 1·6±1·4 (IPL); P<0·01; visual analogue scale] but could be conducted faster [33·1±3·8 s (DL) vs. 40·1±5·0 s (IPL); P<0·01]. No severe side-effects were observed for either therapy. Both DL and IPL treatments are highly effective, long lasting and safe. DL was found to be more effective than IPL treatment. DL treatment was more painful but less time-consuming than IPL therapy.

Femtosecond laser based on Yb:KYW crystals with suppression of spectral narrowing in a regenerative amplifier by spectral profiling of the pulse

This paper describes a femtosecond laser regenerative amplifier based on two Yb:KYW crystals with direct longitudinal pumping by powerful linear arrays of semiconductor injection lasers having fiber output. To prevent spectral narrowing during amplification and the corresponding lengthening of the amplified pulse when it is compressed, a combination of two Yb:KYW crystals were used, with the spectral maxima of the amplification shifted relative to each other and with spectral profiling of the amplified radiation. The mean power of the laser before compression reached 12 W at a pulse-repetition rate in the range 50–500 kHz and a spectral width of 10 nm, which is about a factor of 2 greater than the spectral width without profiling. The pulse width after compression in the compressor equalled 182 fs, while the mean power exceeded 8 W. The laser system thus developed can be used as a source of powerful femtosecond light pulses for the microprocessing of materials and for biomedical applications.

Note: Broadband cavity ring-down spectroscopy of an intra-cavity bulk sample

A cavity ring-down (CRD) setup equipped with a pulsed broadband light source (480 nm ≤ λ ≤ 650 nm) and a multichannel detection system (temporal gate width Δτ = 20 ns) is used to simultaneously record the optical loss spectrum of an intra-cavity CaF2 sample and its changes upon transverse ArF laser irradiation at 193 nm. The CRD setup with mirrors of high reflectivity (R > 99.93%) allows to register loss changes of 5 × 10(-5) with a spectral resolution of 0.3 nm in less than 2 min.

Rejection of Aliased Disturbances in a Production Pulsed Light Source

We study a disturbance rejection problem in a production pulsed light source, used in semiconductor photolithography, to yield quantifiable and guaranteed improved performance over existing control techniques. The disturbances of interest include an offset with reset properties and sinusoids which appear aliased in the measured data which is available only at pulse events. The light source is pulsed at varying rates yet actuators move in continuous-time, yielding a system which blends aspects of continuous-time and variable-data-rate discrete-time. We employ novel modifications to standard continuous-discrete Kalman filtering ideas for disturbance state estimation and establish and solve a non-standard regularized minimum variance control problem within a disturbance rejection framework. The controller as discussed is now in production in semiconductor lithography manufacturing lines. We analyze data from these production light sources and show the controller has the capacity to remove aliased sinusoids from the measured output and yields operational performance levels provably close to optimal for the hardware.

All-fiber time-delay spectrometer for simultaneous spectral and temporal laser pulse characterization in the nanosecond range

We have realized a modified time-delay spectrometer based on a step-chirped fiber Bragg grating array. This method allows simultaneous spectral and temporal characterization of pulsed light sources in the nanosecond regime, which can also be applied to the investigation of single pulses. With a spectral resolution in the 100 pm range, pulse spectrograms are measured and exemplarily used to explore the emission behavior of a wavelength-stabilized laser diode directly modulated in the nanosecond range.

Measurements of Fluorescence Decay Times by the Digital Parallel Frequency-Domain Method (FLIMbox)

The digital parallel frequency domain design is a powerful approach that offers the possibility to implement a variety of different applications in fluorescence spectroscopy and microscopy. It allows lifetime measurements in a cuvette, fluorescence lifetime imaging and FCS as well as multi frequency and multi wavelength tissue imaging in small portable medical devices. It dramatically reduces the acquisition time from the several minutes scale to the seconds scale, and performs every signal process in a digital fashion, avoiding any RF emission and it is extremely inexpensive. This development is the result of a systematic study carried on the previous design known as the FLIMbox. The extensive work done in maximizing the performance of the original FLIMbox led us to develop a new hardware solution with exciting and promising results and potentials that were not possible in the previous hardware realizations. The new design permits acquisition of the full harmonic content of the sample response when it is excited with a pulsed light source in one single measurement using the digital mixing principle that was developed in the original FLIMbox. Furthermore, it is very stable, has very low power requirements and higher precision, and allows the multi exponential analysis. The FLIMbox can be synchronized with lasers that are intrinsically modulated or can generate a frequency to amplitude modulate a laser diode or LED. It provides up to four input channels, it has a saturation feedback control to avoid any time information loss, and it is only limited by the number of photons collected rather than by the sampling window implementation scheme. Work supported by NIGMS, 8P41GM103540.

Laser and light based treatments of acne

Medical treatments for acne vulgaris include a variety of topical and oral medications. Poor compliance, lack of durable remission, and potential side effects are common drawbacks to these treatments. Therefore, there is a growing demand for a fast, safe, and side-effect-free novel therapy. Acne often improves after exposure to sunlight, and this has led to the development of laser and other light therapies resulting in the overall ease of treatment, with minimal adverse effects. A variety of light and laser devices has been used for the treatment of acne, including the potassium titanyl phosphate laser, the 585- and 595-nm pulsed dye lasers, the 1450-nm diode laser, radiofrequency devices, intense pulsed light sources, and photodynamic therapy using 5-aminolevulinic acid and indocyanine green. These devices are thought to target the underlying pathogenic factors such as propionibacterium acnes colonization, increased sebaceous gland activity, and the cutaneous inflammatory response. In this article, we review the current status of light- and laser-based treatment of acne.

Characterization of optical properties of the site of the ANTARES neutrino telescope

ANTARES is a neutrino detector based on a three-dimensional grid of photomultipliers tubes (PMT's) arranged in several detection lines anchored to the seabed at depth of 2.5km in the Mediterranean Sea (40km off the Toulon coast in France), its main physics goal is the reconstruction and identification of high energy neutrinos of extra-terrestrial origin. The PMT's register the Cherenkov light induced by relativistic charged leptons produced by the interaction of neutrinos with material in the detector surroundings. The propagation of Cherenkov light strongly depends on the optical properties of the sea water, the understanding of which is crucial in order to achieve the expected detector performance. To reach the ANTARES physics goals, good time and positioning calibration systems are required.The ANTARES optical beacon system consists of a set of pulsed light sources strategically located throughout the detector. The system is mainly used for time calibration but can also be used as a tool to study the water optical properties and their stability. In this contribution we will present the current status of our measurements of the group velocity and transmission length of light carried out between 2008 and 2011. A set of water models strategically defined will be discussed as well as some preliminary results concerning track reconstruction parameters.

Long-Term Removal of Unwanted Hair Using Light

Laser (or light) hair removal, also referred to as photoepilation, is the most commonly used laser or light-based cosmetic medical procedure. The extended theory of selective photothermolysis is the basic principle for destruction of hair follicles using light. In this type of laser application the chromophore is follicular melanin. Several types of lasers and light sources have been effective for hair reduction, including the ruby, alexandrite, diode, and neodymium:yttrium-aluminum-garnet lasers and broadband, intense pulsed light sources. This article provides a broad overview of how hair can be removed using light, with an emphasis on practical considerations.

A comparative study of hair removal at an NHS hospital: luminette intense pulsed light versus electrolysis

Twenty-five women, referred for hair removal by electrolysis, were enrolled in a split face study to treat facial hirsutism. Each patient was treated on six occasions: one-half of the face with electrolysis and the other side with an intense pulsed light source. Patients were evaluated with respect to reduction in hair counts, side effects and discomfort during treatment. Re-growth was assessed at 3, 6 and 9 months following treatment. All patients, except one with very sparse, fair hair growth, preferred treatment with the Intense Pulsed Light and rated their average hair reduction with this method as 77% after five treatments. The overall patient satisfaction rates as determined by visual analogue scales were 8.3 out of 10 for IPL and 5.4 out of 10 for electrolysis.

A compact pyrodetector for measuring the radiation energy of pulsed plasma light sources in the vacuum ultraviolet

A compact noise-resistant pyroelectric calorimeter has been developed in which radiation is spectrally selected by quartz and inert-gas filters. The calorimeter is intended both for measuring the spectroenergetic characteristics of powerful pulsed plasma radiators and for measuring the surface irradiance of test objects in a 2π-sr solid angle. The calorimeter has been calibrated in energy, and the results have been confirmed by thermocouple measurements.

An all-photonic-crystal-fiber wavelength-tunable source of high-energy sub-100 fs pulses

We demonstrate a wavelength-tunable source of high-energy sub-100fs light pulses where all the key components, including a master oscillator, an amplifier, and a tunable frequency shifter, are based on photonic-crystal fibers (PCFs). Soliton self-frequency shift in a specifically designed all-solid photonic band-gap fiber with an effective mode area of 110μm2 is used in this system to transform a 1040nm, 50MHz, 100fs amplified output of a large-mode-area ytterbium-doped PCF oscillator–amplifier system into sub-100fs, 6.4nJ light pulses smoothly tunable within the range of wavelengths from 1160 to 1260nm.

High harmonics with a twist

Optical vortices usually break up when they propagate through nonlinear media. Now, however, experiments show the helical structure of an infrared beam can survive a high-harmonic-generation process. This could lead to a table-top source of attosecond helical light pulses.

Time-Resolved Diffuse Optical Spectroscopy up to 1700 nm by Means of a Time-Gated InGaAs/InP Single-Photon Avalanche Diode

We present a new compact system for time-domain diffuse optical spectroscopy of highly scattering media operating in the wavelength range from 1100 nm to 1700 nm. So far, this technique has been exploited mostly up to 1100 nm: we extended the spectral range by means of a pulsed supercontinuum light source at a high repetition rate, a prism to spectrally disperse the radiation, and a time-gated InGaAs/InP single-photon avalanche diode working up to 1700 nm. A time-correlated single-photon counting board was used as processing electronics. The system is characterized by linear behavior up to absorption values of about 3.4 cm(-1) where the relative error is 17%. A first measurement performed on lipids is presented: the absorption spectrum shows three major peaks at 1200 nm, 1400 nm, and 1700 nm.

Fast and effective: intense pulse light photodynamic inactivation of bacteria

The goal of this study was to investigate the photodynamic toxicity of TMPyP (5, 10, 15, 20-Tetrakis (1-methylpyridinium-4-yl)-porphyrin tetra p-toluenesulfonate) in combination with short pulses (ms) of an intense pulse light source within 10 s against Bacillus atrophaeus, Staphylococcus aureus, Methicillin-resistant S. aureus and Escherichia coli, major pathogens in food industry and in health care, respectively. Bacteria were incubated with a photoactive dye (TMPyP) that is subsequently irradiated with visible light flashes of 100 ms to induce oxidative damage immediately by generation of reactive oxygen species like singlet oxygen. A photodynamic killing efficacy of up to 6 log(10) (>99.9999%) was achieved within a total treatment time of 10 s using a concentration range of 1-100 μmol TMPyP and multiple light flashes of 100 ms (from 20 J cm(-2) up to 80 J cm(-2)). Both incubation of bacteria with TMPyP alone or application of light flashes only did not have any negative effect on bacteria survival. Here we could demonstrate for the first time that the combination of TMPyP as the respective photosensitizer and a light flash of 100 ms of an intense pulsed light source is enough to generate sufficient amounts of reactive oxygen species to kill these pathogens within a few seconds. Increasing antibiotic resistance requires fast and efficient new approaches to kill bacteria, therefore the photodynamic process seems to be a promising tool for disinfection of horizontal surfaces in industry and clinical purposes where savings in time is a critical point to achieve efficient inactivation of microorganisms.

Laser 3D micro/nanofabrication of polymers for tissue engineering applications

In this work, we applied a constructed multi-photon polymerization system based on diode-pumped solid state femtosecond Yb:KGW laser used as pulsed irradiation light source (300fs, 1030nm, 200kHz) in combination with large area high sample translation velocity (up to 300mm/s) linear motor-driven stages (100×100×50mm3) designed for high resolution and throughput 3D micro/nanofabrication. It enables rapid prototyping out of most polymers up to cm in scale with sub-micrometer spatial resolution. This can be used for production of three-dimensional artificial polymeric scaffolds applied for cell growth and expansion experiments as well as tissue engineering. Biocompatibilities of different acrylate, hybrid organic–inorganic and biodegradable polymeric materials were evaluated experimentally in vitro. Various in size and form scaffolds of biocompatible photopolymers were successfully fabricated having intricate 3D geometry, thus demonstrating the potential of the applied method. Adult rabbit myogenic stem cell proliferation tests show artificial scaffolds to be applicable for biomedical practice. Additionally, a micromolding technique was used for a rapid multiplication of adequate laser manufactured structures.

High peak-power picosecond pulse generation at 126 µm using a quantum-dot-based external-cavity mode-locked laser and tapered optical amplifier

In this paper, we present the generation of high peak-power picosecond optical pulses in the 1.26 μm spectral band from a repetition-rate-tunable quantum-dot external-cavity passively mode-locked laser (QD-ECMLL), amplified by a tapered quantum-dot semiconductor optical amplifier (QD-SOA). The laser emission wavelength was controlled through a chirped volume Bragg grating which was used as an external cavity output coupler. An average power of 208.2 mW, pulse energy of 321 pJ, and peak power of 30.3 W were achieved. Preliminary nonlinear imaging investigations indicate that this system is promising as a high peak-power pulsed light source for nonlinear bio-imaging applications across the 1.0 μm - 1.3 μm spectral range.

Direct two-photon excitation of Sm3+, Eu3+, Tb3+, Tb.DOTA−, and Tb.propargylDO3A in solution

We have observed direct two-photon excitation of samarium, europium and terbium ions in solution upon near IR excitation using a tuneable pulsed light source, and have also studied two-photon processes in a pair of related terbium complexes, namely [Tb.DOTA]− and Tb.propargylDO3A. Direct two-photon excitation of lanthanides is observed in simple systems in the absence of sensitizing chromophores. Where even simple chromophores such as a triple bond are present in the complex, then single and two-photon excitation of chromophore excited states competes with direct two-photon excitation of the ions and is the dominant pathway for sensitizing formation of the lanthanide excited state.