Diode Laser System Research Articles

Technical note: Laboratory evaluation of a tunable diode laser system for eddy covariance measurements of ammonia flux

A tunable diode laser trace gas analyzer (TGA 100, Campbell Scientific, Logan, Utah) was evaluated in the laboratory for its ability to measure ammonia fluxes using the eddy covariance technique. A random noise generator was used in the laboratory to switch sampling between high and low concentration air streams to simulate a range of eddy sizes with a known input. A mechanical switching system was developed to prevent pressure fluctuations during switching associated with valves. A half-power point of 0.4 Hz was found for 50 m of sampling tubing. Resolution, determined through laboratory tests, was conservatively estimated between 0.2 and 1 μg m −2 s −1.

A frequency stabilization technique for diode lasers based on frequency-shifted beams from an acousto-optic modulator

We present a simple method for diode laser frequency stabilization that makes use of a Doppler-broadened vapor cell absorption signals of two frequency-shifted laser beams. Using second-order-diffracted, double-passed beams from an acousto-optic modulator, we achieve a frequency separation roughly equal to the Doppler half width. The differential transmission signals of the two beams provide an error signal with a very large linear feature, allowing frequency stabilization over a range of greater than 1 GHz by means of standard proportional-integral-derivative servo feedback to the piezoelectric control of the grating in our external cavity diode laser. We have applied this technique to two different diode laser systems, one used to lock to the 410 nm E1 transition in indium and another for locking to the M1/E2 transition in thallium at 1283 nm. In both cases the technique reduces frequency fluctuation to roughly 1 MHz over time scales from 10(-3) to 10(2) s.

In vitro study of the pulp chamber temperature rise during light-activated bleaching

This study evaluated in vitro the pulp chamber temperature rise induced by the light-activated dental bleaching technique using different light sources. The root portions of 78 extracted sound human mandibular incisors were sectioned approximately 2 mm below the cementoenamel junction. The root cavities of the crowns were enlarged to facilitate the correct placing of the sensor into the pulp chamber. Half of specimens (n=39) was assigned to receive a 35% hydrogen peroxide gel on the buccal surface and the other halt (n=39) not to receive the bleaching agent. Three groups (n=13) were formed for each condition (bleach or no bleach) according to the use of 3 light sources recommended for dental bleaching: a light-emitting diode (LED)-laser system, a LED unit and a conventional halogen light. The light sources were positioned perpendicular to the buccal surface at a distance of 5 mm and activated during 30 s. The differences between the initial and the highest temperature readings for each specimen were obtained, and, from the temperature changes, the means for each specimen and each group were calculated. The values of temperature rise were compared using Kruskal-Wallis test at 1% significance level. Temperature rise varied significantly depending on the light-curing unit, with statistically significant differences (p<0.01) among the groups. When the bleaching agent was not applied, the halogen light induced the highest temperature rise (2.38±0.66°C). The LED unit produced the lowest temperature increase (0.29±0.13°C); but there was no significant difference between LED unit and LED-laser system (0.35±0.15°C) (p>0.01). When the bleaching agent was applied, there were significant differences among groups (p<0.01): halogen light induced the highest temperature rise (1.41±0.64°C), and LED-laser system the lowest (0.33±0.12°C); however, there was no difference between LED-laser system and LED unit (0.44±0.11°C). LED and LED-laser system did not differ significantly from each other regardless the temperature rise occurred with or without bleaching agent application. It may be concluded that during light-activated tooth bleaching, with or without the bleaching agent, halogen light promoted higher pulp chamber temperature rise than LED unit and LED-laser system. The tested light-curing units provided increases in the pulp chamber temperature that were compatible with pulpal health.

Chemical Sensor Networks for Gas Detection and Environmental Monitoring

This paper reviews the principles and prospects for optical fibre based measurement techniques for determining gas concentrations. Most of these exploit the precision and versatility of tuneable diode laser spectroscopy in the near infrared. We demonstrate the potential offered by large area multipoint totally passive networks and establish the performance potential which these may offer in hostile environments. These benefits include more than adequate sensitivity for most applications, automatic recalibration of both zero point and scale factor and the ability to precisely determine line shape information and in some cases perform detailed line spectrum analysis to determine concentration, pressure and temperature simultaneously. We also briefly describe the principles and application of photo acoustic spectroscopy and outline the performance improvements which tuneable diode laser systems also offer in this context. These studies have illustrated that, in appropriate niche applications, fibre based gas measurement systems offer substantial long term engineering potential.

Wavelength-Stabilized Compact Diode Laser System on a Microoptical Bench With 1.5-W Optical Output Power at 671 nm

A wavelength-stabilized compact diode laser system emitting at 671 nm mounted on a microoptical bench with the dimensions of 13 mmtimes4 mm is presented. A reflecting Bragg grating was aligned on the rear side of a broad-area gain medium for wavelength stabilization at 671 nm. A maximum output power of 1.5 W was obtained together with a spectral width of 40 pm (full-width at half-maximum). At 1.0 W, a center wavelength stability below 20 pm over 5 h was determined. With these features, the devices are well-suited for spectroscopic applications.

Scar Prevention by Laser‐Assisted Scar Healing (LASH): A pilot study using an 810‐nm diode‐laser system

Normal wound healing of the skin results in a flat and flexible scar. The ideal end point would be total regeneration, with the new tissue having the same structural, aesthetic, and functional attributes as the original uninjured skin. Scars are often considered trivial, but they can be disfiguring and aesthetically unpleasant and cause severe itching, tenderness, pain, sleep disturbance, anxiety, and depression [1]. Cosmetic results obtained after skin surgery are a key component of patient satisfaction. Surgical skin scars are a type of scar that can benefit from laser therapy. Redness and telangiectasia developing in such scars usually spontaneously remit, but often slowly and incompletely. Laser can not only accelerate this decolorizing process, it can also advance the end point closer to the complete absence of redness with improvement in scar texture and pliability with minimal side effects [2]. Recently, Capon et al. [3] showed the ability of a 815-nm diode-laser system to assist wound closure leading to an acceleration and an improvement of wound healing with indiscernible resulting scar in hairless rats. The purpose of this study was to improve the appearance of scars, by improving through a thermal action the wound healing process. This thermal action was generated by an 810-nm laser source. This specific wavelength choice ensured a minimal epidermal damage as neither blood nor water can absorb at this wavelength. This pilot study aimed at evaluating the 810-nm diode-laser system to accelerate and improve the healing process in surgical scars, immediately after skin closure, of patients with Fitzpatrick skin type I–IV. Five patients (five females) with Fitzpatrick skin types I–IV and fresh surgical scars of greater than 2 cm (i.e., horizontal scars from abdominoplasty) were enrolled in this prospective pilot study (Table 1). This clinical trial has been approved by the Ethics Committee (Comite Consultatif de Protection des Personnes en Recherche Biomedicale (CCPPRB) de la region Nord Pas-de-Calais). Patients under 18 years of age, with dark skin (phototypes V or VI), pregnant women, and patients with a history of malignant tumor skin disease, bacterial or viral infectious skin disease, immunosuppression and treated by a longterm corticosteroids treatment were excluded. Patients were treated with fluence comprised between 80 and 120 J/ cm, in order to evaluate safety and performance of the 810-nm diode-laser system. Each surgical incision was divided into two fields, with 8 cm receiving an 810-nm diode-laser treatment (4 mm diameter beam, continuous wave, total exposure duration: 3–4 seconds). The other part was not treated. Treated and untreated portions were selected randomly. Scars were evaluated for pigmentation, vascularity, pliability, and height by surgeon and patient at 10 days, 3 months, and 12 months. A comparative scar evaluation based on cosmetic appearance using a visual analog scale from 5 (worst) to 5 (best) was performed by surgeon and patients. Overall appearance ratings ranging from an optimum of 1 to a minimum of 4 (11⁄4 excellent, 21⁄4 good,

Frequency stabilization of an ultraviolet laser to ions in a discharge

We stabilize an ultraviolet diode laser system at 369.5 nm to the optical absorption signal from Yb+ ions in a hollow-cathode discharge lamp. The error signal for stabilization is obtained by Zeeman spectroscopy of the 3 GHz wide absorption feature. The frequency stability is independently measured by comparison to the fluorescence signal from a laser-cooled crystal of Y174b+ ions in a linear Paul trap. We measure a frequency fluctuation of 1.7 MHz over 1000 s and a frequency drift of 20 MHz over 7 days. Our method is suitable for use in quantum information processing experiments with trapped ion crystals.

High brightness, tunable biphoton source at 976 nm for quantum spectroscopy

A compact all solid state continuous-wave biphoton source, tunable around 488 nm, for quantum spectroscopic applications based on a frequency doubled diode laser system is presented. Copolarized photon pairs in the fundamental transversal mode could be generated at 976 nm by spontaneous parametric down conversion inside a type-0 quasi phase matched periodically poled lithium niobate waveguide crystal with an efficiency of 8-10(-6). A high flux rate greater than 10(7) photon pairs per second has been achieved at pump powers in the muW range resulting in more than 7-10(9) photon pairs/s-mW. Further a detailed investigation of the spectral behavior and the flux rate as a function of the detuning from the degenerated case is presented.

Ex vivo and in vivo investigations of the novel 1,470 nm diode laser for potential treatment of benign prostatic enlargement

Perioperative haemorrhage is still the major complication of transurethral resection of the prostate (TURP) for benign enlargement of the prostate. Photoselective vaporisation of the prostate (PVP) with the potassium-titanyl-phosphate (KTP) laser has been shown to achieve instant tissue ablation with excellent haemostatic properties. Our aim was to determine the tissue removal capacity, coagulation and haemostatic property of the novel 1,470 nm diode laser, ex vivo and in vivo. We evaluated two prototype diode laser systems at 1,470 nm in an ex vivo, isolated, blood-perfused, porcine kidney model (n = 5; 10 W-50 W) and in an in vivo investigation of beagle prostate (n = 4; 100 W) to assess vaporisation capacities and coagulation properties at different generator settings. The diode laser evaluation was compared with an 80 W KTP laser in the porcine model. After the laser treatment we performed a histological examination to compare the depth of coagulation and vaporisation. The diode laser system (50 W) showed significantly lower (P < 0.0001) capacities for tissue removal than the 80 W KTP laser (0.96 mm +/- 0.17 mm and 5.93 mm +/- 0.25 mm, respectively, P < 0.0001), while coagulation zones were significantly (P < 0.001) larger in diode laser-treated kidneys (3,39 mm +/- 0.93 mm and 1.27 mm +/- 0.13 mm, respectively). In vivo, the diode laser displayed rapid ablation of prostatic tissue with no intraoperative haemorrhage. Histological examination revealed coagulation zones of 2.30 mm (+/-0.26) at 100 W in the diode laser-treated prostates.

A Direct Diode Laser System Using a Planar Lightwave Circuit

In this paper we propose a direct diode laser (DDL) system consisting of laser diode (LD) bars, a planar lightwave circuit (PLC), and an optical fiber. We have developed a PLC as an optical power combiner and an LD mounting technology that is suitable for coupling to the PLC. A DDL system is presented that consists of six LD-PLC optical modules for the laser-welding of highly heat-resistant plastics. The total output power is in the 200 W class, with a spot diameter of 5.52 mm for the major axis and 5.00 mm for the minor axis at a focal length of 50 mm. The total output efficiency is 60.9% from the laser diode to the welding torch.

Narrow-Line and Frequency Tunable Diode Laser System for S–D Transition of Ca+ Ions

A new type of diode laser is used for the development of an extremely narrow linewidth and frequency-tunable clock laser system for a Ca+ ion optical frequency standard. The required reduction of linewidth was achieved by locking the laser to an ultrahigh-finesse ultralow-expansion glass (ULE) reference cavity. The long-term frequency drift is reduced by stabilizing a cavity temperature at the point that the thermal expansion coefficient of the ULE is zero. As a result, the laser linewidth is decreased to lower than 25 Hz and the long-term drift is less than 0.025 Hz/s. The other laser offset locked to the stabilized laser is continuously frequency tunable in the entire free spectral range of the reference cavity without degradation of stability and linewidth. This laser system is actually applied to optical frequency standard development and used for the observation of the 2S1/2–2D5/2 transition of Ca+ ions.

A simple readout electronics for automatic power controlled self-mixing laser diode systems

The paper describes a simple electronic circuit to drive a laser diode for self-mixing interferometry. The network integrates a stable commercial automatic power controller and a current mirror based readout of the interferometric signal. The first prototype version of the circuit has been realized and characterized. The system allows easily performing precise interferometric measurements with no thermostatic circuitry to stabilize the laser diode temperature and an automatic control gain network to compensate emitted optical power fluctuations. To achieve this result, in the paper a specific calibration procedure to be performed is described.

A narrow-line-width external cavity quantum dot laser for high-resolution spectroscopy in the near-infrared and yellow spectral ranges

We demonstrate a diode laser system which is suitable for high-resolution spectroscopy in the 1.2 μm and yellow spectral ranges. It is based on a two-facet quantum dot chip in a Littrow-type external cavity configuration. The laser is tunable in the range 1125–1280 nm, with an output power of more than 200 mW, and exhibits a free-running line width of 200 kHz. Amplitude and frequency noise were characterized, including the dependence of the frequency noise on the cavity length. Frequency stabilization to a high-finesse reference cavity is demonstrated, whereby the line width was reduced to approx. 30 kHz. Using a femtosecond frequency comb, the residual frequency instability was determined and found to be below 300 Hz on the time scales 1–300 s. Yellow light (>3 mW) at 578 nm was generated by frequency doubling in an enhancement cavity containing a PPLN crystal. The source has potential application for precision spectroscopy of ultra-cold Yb atoms and cold molecular hydrogen ions.

InGaAs diode laser system generating pulses of 580 fs duration and 366 W peak power

This paper reports the generation of fs light pulses by a passively mode-locked InGaAs master oscillator power amplifier (MOPA) system. The laser system generates chirped pulses with 6.2 ps duration, a center wavelength of 922 nm and 4 GHz repetition rate. Pulse compression by an external grating compressor reduces the pulse duration to 580 fs. The average power of the compressed pulses of 851 mW corresponds to a peak power of 366 W.

Laser Joining Applications Highest Efficiency Using Diode Lasers

Laser technology is becoming more and more the only method of joining which can stand up to the high demands of modern production processes in the automotive industry, such as high reproducibility, minimal heat-affected zones and the special esthetic requirements made on the seams. In addition to Nd:YAG lasers, which have already established themselves in this field, the use of diode lasers is now becoming increasingly common. The principal reasons for this are the financial benefits in combination with the high beam quality and the reliability of modern diode laser systems as seen, for example, in brazing and heat conduction welding in the mass production applications of the automotive industry.

Frequency comb-referenced narrow line width diode laser system for coherent molecular spectroscopy

We analyze in detail the frequency noise properties of a grating enhanced external cavity diode laser (GEECDL). This system merges two diode laser concepts, the grating stabilized diode laser and the diode laser with resonant optical feedback, thus combining a large tuning range with an excellent short-term frequency stability. We compare the frequency noise spectrum of a GEECDL to that of a grating stabilized diode laser and demonstrate a 10-fold reduction of the frequency noise linear spectral density. The GEECDL is phase locked to a similar laser and to a fs-frequency comb with a servo loop providing an open-loop unity-gain frequency of only 237 kHz, which is a tenth of the bandwidth typically required for grating stabilized diode lasers. We achieve a residual rms phase error as small as 72 mrad (≈ 200 mrad) for stabilization to a similar laser (to the fs-frequency comb). We demonstrate that the novel diode laser can phase-coherently track a stable optical reference with an instability of 1.8×10-16 at 1 s. This laser system is well suited for applications that require phase locking to a low-power optical reference under noisy conditions. It may also be considered for the implementation of optical clock lasers.

A diode laser system for spectroscopy of the ultranarrow transition in ytterbium atoms

A narrow-line diode laser system has been developed for high-resolution spectroscopy of the magnetic quadrupole transition in ytterbium (Yb) atoms at 507 nm. The system consists of an extended-cavity laser diode at 1014 nm, a tapered amplifier and a periodically poled lithium niobate nonlinear crystal which converts the wavelength from 1014 nm to 507 nm. We have stabilized the laser frequency and reduced the linewidth below 1 kHz by tightly locking the laser to a high-finesse optical cavity. By using the developed laser system, we have successfully observed the ultranarrow

High-power diode laser at 980 nm for the treatment of benign prostatic hyperplasia: ex vivo investigations on porcine kidneys and human cadaver prostates

Diode laser systems at 980 nm have been introduced for the treatment of lower-urinary-tract-symptoms (LUTS) suggestive of benign prostatic enlargement (BPE). However, the coagulation and vaporization properties are unknown. We therefore aimed to evaluate these properties in ex vivo models in comparison with the kalium-titanyl-phosphate-(KTP) laser. The diode laser treatment was applied to isolated, blood-perfused porcine kidneys and fresh human cadaver prostates (HCPs) at different generator settings. We performed histological examination to compare the depth of coagulation and vaporization. The diode laser showed larger ablation and coagulation characteristics than the KTP laser did. Ablation of the diode laser was found to be 1.79-times (120 W in porcine kidney, P < 0.0001) and 3.0-5 times (200 W in HCP, P < 0.0005) larger. The diode laser created a nine-times (120 W in porcine kidney, P < 0.0001) and seven-times (200 W in HCP, P < 0.0001) deeper necrosis zone. The diode laser vaporization was highly effective ex vivo. Owing to the laser's deep coagulation zones, in vivo animal experiments are mandatory before the diode laser (980 nm) is applied in a clinical setting, so that damage to underlying structures is prevented.

Signal processing system in cavity enhanced spectroscopy

AbstractThe paper presents a signal processing system used for nitrogen dioxide detection employing cavity enhanced absorption spectroscopy. In this system, the absorbing gas concentration is determined by the measurement of a decay time of a light pulse trapped in a cavity.The setup includes a resonance optical cavity, which was equipped with spherical and high reflectance mirrors, the pulsed diode laser (414 nm) and electronic signal processing system. In order to ensure registration of low-level signals and accurate decay time measurements, special preamplifier and digital signal processing circuit were developed.Theoretical analyses of main parameters of optical cavity and signal processing system were presented and especially signal-to-noise ratio was taken into consideration. Furthermore, investigation of S/N signal processing system and influence of preamplifier feedback resistance on the useful signal distortion were described.The aim of the experiment was to study potential application of cavity enhanced absorption spectroscopy for construction of fully optoelectronic NO2 sensor which could replace, e.g., commonly used chemical detectors. Thanks to the developed signal processing system, detection limit of NO2 sensor reaches the value of 0.2 ppb (absorption coefficient equivalent = 2.8 × 10−9 cm−1).

Ultrastructural evidence for thermal injury to pilosebaceous units during the treatment of acne using photopneumatic (PPX) therapy

Background and objective: Acne is a very prevalent skin disorder, and several devices, such as blue light, pulsed dye laser, diode laser, LED, RF and pulsed light systems, have been reported to have varying degrees of efficacy for treatment. Photopneumatic therapy (PPX) is a novel technology that combines pneumatic energy with a broadband light source to manipulate the optical characteristics of the skin. A vacuum suction raises target structures in the dermis closer to the surface of the skin prior to exposure, allowing for more efficient energy transmission. This study tested the hypothesis that a combination of pulsed light and suction would affect sebaceous plugging within diseased pilosebaceous apparati at a histological level, resulting in the rapid clearance of acne lesions. Methods: Eight individuals were treated with PPX once per week for a total of five treatments. Punch biopsies of the treated areas were obtained just after the first exposure, just before the third exposure and immediately after the fifth exposure. Those specimens were examined by conventional and by electron microscopy for any alterations following treatment. Results: Immediately following the first treatment, the mechanical extrusion of comedo contents from the infundibulum was observed histologically. One week after the second treatment, thermally injured bacteria as well as direct thermal injury to pilosebaceous apparati were observed ultrastructurally. Conclusion: These results correlate with clinical reports on decreased sebaceous gland activity after PPX treatment and may mechanistically give rise to the rapid regression of acne lesions.