Continuous Wave Diode Laser Research Articles

60-W continuous wave laser diode arrays emitting at a wavelength of 808 nm

Samples of cw laser diode arrays (LDAs) with an output power higher than 60 W emitting in the spectral range of 808 nm are developed and fabricated. Main output parameters, including light–current, current–voltage characteristics, and emission spectra of a lot of 5 LDAs are measured.

Laser Acupuncture Treatment Improves Pain and Functional Status in Patients with Subacromial Impingement Syndrome: A Randomized, Double-Blind, Sham-Controlled Study.

The present study aims to determine the effect of laser acupuncture in patients with subacromial impingement syndrome (SAIS). Randomized, double-blind, sham-controlled study. Physical medicine and rehabilitation outpatient clinic. A total 73 patients with SAIS were randomly assigned into a treatment group (n = 36) and a control group (n = 37). The treatment group received laser acupuncture, and the control group received sham laser acupuncture. Eleven acupuncture points (GB 21, LI 4, LI 11, LI 14, LI 15, LI 16, SI 9, SI 10, SI 11, TE 14, and TE 15) were irradiated using a gallium-aluminium-arsenide continuous wave diode-laser, with a wavelength of 850 nm and a power output of 100 mV. The laser acupuncture treatment at each acupuncture point was administered at 4 joules/cm 2 (total dose = 40 joules). All patients were also treated with a hot pack. The patients were assessed at baseline and after 15 sessions of laser treatment. Pain severity and doctor's and patient's global assessments were measured via visual analog scale (VAS). Range of motion (ROM) and functional status were measured using a digital inclinometer and the Shoulder Pain Disability Index, respectively. Statistically significant improvements were observed in all parameters in the treatment group. All parameters of pain and functional status in the treatment group were significantly better than those in the control group at week 3. To the best of our knowledge, this is the first study that investigates the effect of laser acupuncture in SAIS. The positive results of the present study should lead to further laser acupuncture studies with combinations of different acupuncture points, at different wavelengths, and with long-term follow-up periods.

Third-order nonlinear optical properties of acid green 25 dye by Z─scan method

Third-order nonlinear optical (NLO) properties of aqueous solutions of an anthraquinone dye (Acid green 25 dye, color index: 61570) have been studied by Z─scan method with a 5mW continuous wave (CW) diode laser operating at 635nm. The nonlinear refractive index (n2) and the absorption coefficient (β) have been evaluated respectively from the closed and open aperture Z─scan data and the values of these parameters are found to increase with increase in concentration of the dye solution. The negative sign of the observed nonlinear refractive index (n2) indicates that the aqueous solution of acid green 25 dye exhibits self-defocusing type optical nonlinearity. The mechanism of the observed nonlinear absorption (NLA) and nonlinear refraction (NLR) is attributed respectively to reverse saturable absorption (RSA) and thermal nonlinear effects. The magnitudes of n2 and β are found to be of the order of 10−7cm2/W and 10−3cm/W respectively. With these experimental results, the authors suggest that acid green 25 dye may have potential applications in nonlinear optics.

Terahertz parametric generation and amplification from potassium titanyl phosphate in comparison with lithium niobate and lithium tantalate.

We report superior terahertz parametric generation from potassium titanyl phosphate (KTP) over congruent-grown lithium niobate (CLN) and lithium tantalate (CLT) in terms of parametric gain and laser damage resistance. Under the same pump and crystal configurations, the signal emerged first from KTP, 5% Mg-doped CLN, CLN, and then finally from CLT. The signal growth rate in KTP was comparable to that in 5%-Mg-doped CLN, but the signal power from KTP reached a much higher value after all the other crystals were damaged by the pump laser. We further demonstrate seeded terahertz parametric amplification in an edge-cut KTP at 5.74 THz. The THz parametric amplifier (TPA) employs a 17-mm long KTP gain crystal, pumped by a passively Q-switched pump laser at 1064 nm and seeded by a continuous-wave diode laser tuned to the signal wavelength at 1086.2 nm. With 5.8-mJ energy in a 520-ps pump pulse and 100-mW seed signal power, we measured 5-W peak-power THz output from the KTP TPA with 22% pump depletion. In comparison, we measured no detectable THz output power from a similar edge-cut CLN TPA under the same pump power, detection scheme, and crystal configuration, when tuning the seed laser wavelength to 1072.2 nm and attempting to generate a radiation at 2.1 THz.

Combined frequency domain photoacoustic and ultrasound imaging for intravascular applications.

Intravascular photoacoustic (IVPA) imaging has the potential to characterize lipid-rich structures based on the optical absorption contrast of tissues. In this study, we explore frequency domain photoacoustics (FDPA) for intravascular applications. The system employed an intensity-modulated continuous wave (CW) laser diode, delivering 1W over an intensity modulated chirp frequency of 4-12MHz. We demonstrated the feasibility of this approach on an agar vessel phantom with graphite and lipid targets, imaged using a planar acoustic transducer co-aligned with an optical fibre, allowing for the co-registration of IVUS and FDPA images. A frequency domain correlation method was used for signal processing and image reconstruction. The graphite and lipid targets show an increase in FDPA signal as compared to the background of 21dB and 16dB, respectively. Use of compact CW laser diodes may provide a valuable alternative for the development of photoacoustic intravascular devices instead of pulsed laser systems.

Single-frequency tunable 447.3 nm laser by frequency doubling of tapered amplified diode laser at cesium D1 line.

A continuous single-frequency tunable blue laser at 447.3 nm is developed by external-cavity frequency doubling of a tapered amplifier-boosted continuous-wave diode laser at cesium (Cs) D1 line. A maximum blue power of 178 mW with 50.8% conversion efficiency is obtained. It can be continuously tuned over a range around 1.6 GHz as the diode laser frequency is scanned across the F=4→F'=3 transition of 133Cs D1 line. The generated tunable and stable blue laser source has potential applications in constructing quantum light-atom interfaces in quantum networks.

Silver nanoparticles enhanced photoluminescence of Nd3+ doped germanate glasses at 1064 nm

Infrared photoluminescence (PL) properties of PbO-GeO2 glasses containing neodymium ions (Nd3+) and silver nanoparticles (NPs) were investigated. The excitation was made with a continuous-wave diode laser operating at 805 nm, in resonance with the Nd3+ transition 4I9/2 → 4F5/2. Growth of ∼160% in the PL intensity at 1064 nm, was observed in comparison with a reference sample without silver NPs. The PL enhancement is attributed to the increased local-field in the Nd3+ locations nearby the NPs. The present results indicate that PbO-GeO2 glasses containing Nd3+ and silver NPs have good prospect to be used in optical amplifiers at 1064 nm.

Generating photon pairs from a silicon microring resonator using an electronic step recovery diode for pump pulse generation

Generation of photon pairs from compact, manufacturable, and inexpensive silicon (Si) photonic devices at room temperature may help develop practical applications of quantum photonics. An important characteristic of photon-pair generation is the two-photon joint spectral intensity, which describes the frequency correlations of the photon pair. Recent attempts to generate a factorizable photon-pair state suitable for heralding have used short optical pump pulses from mode-locked lasers, which are much more expensive and bigger table-top or rack-sized instruments compared with the Si microchip used for generating photon pairs, and thus dominate the cost and inhibit the miniaturization of the source. Here, we generate photon pairs from an Si microring resonator by using an electronic step-recovery diode to drive an electro-optic modulator which carves the pump light from a continuous-wave laser diode into pulses of the appropriate width, thus potentially eliminating the need for optical mode-locked lasers.

A highly efficient directional molecular white-light emitter driven by a continuous-wave laser diode.

Tailored light sources have greatly advanced technological and scientific progress by optimizing the emission spectrum or color and the emission characteristics. We demonstrate an efficient spectrally broadband and highly directional warm-white-light emitter based on a nonlinear process driven by a cheap, low-power continuous-wave infrared laser diode. The nonlinear medium is a specially designed amorphous material composed of symmetry-free, diamondoid-like cluster molecules that are readily obtained from ubiquitous resources. The visible part of the spectrum resembles the color of a tungsten-halogen lamp at 2900 kelvin while retaining the superior beam divergence of the driving laser. This approach of functionalizing energy-efficient state-of-the-art semiconductor lasers enables a technology complementary to light-emitting diodes for replacing incandescent white-light emitters in high-brilliance applications.

The role of photobiomodulation on gene expression of cell adhesion molecules in diabetic wounded fibroblasts in vitro

Cell adhesion molecules (CAMs) are cell surface glycoproteins that facilitate cell-cell contacts and adhesion with the extracellular matrix (ECM). Cellular adhesion is affected by various disease conditions, such as diabetes mellitus (DM) and inflammation. Photobiomodulation (PBM) stimulates biological processes and expression of these cellular molecules. The aim of this experimental work was to demonstrate the role of PBM at 830nm on CAMs in diabetic wounded fibroblast cells. Isolated human skin fibroblast cells were used. Normal (N-) and diabetic wounded (DW-) cells were irradiated with a continuous wave diode laser at 830nm with an energy density of 5J/cm2. Real time reverse transcriptase polymerase chain reaction (RT-PCR) was used to determine the relative gene expression of 39 CAMs 48h post-irradiation. Normalized expression levels from irradiated cells were calculated relative to non-irradiated control cells according to the 2^(−ΔΔCt) method. Thirty-one genes were significantly regulated in N-cells (28 were genes up-regulated and three genes down-regulated), and 22 genes in DW-cells (five genes were up-regulated and 17 genes down-regulated). PBM induced a stimulatory effect on various CAMs namely cadherins, integrins, selectins and immunoglobulins, and hence may be used as a complementary therapy in advancing treatment of non-healing diabetic ulcers. The regulation of CAMs as well as evaluating the role of PBM on the molecular effects of these genes may expand knowledge and prompt further research into the cellular mechanisms in diabetic wound healing that may lead to valuable clinical outcomes.

P-7: High Performance LTPS Thin-film Transistors using Low Cost Polycrystalline Silicon by Blue Laser Annealing

Crystallization of amorphous silicon (a-Si) to polycrystalline silicon (p-Si) by a continuous-wave blue laser diode of wavelength 445 nm is investigated for high throughput thin-film transistor applications (TFT). As the laser scan speed is changed at constant laser power, laser scanned p-Si films show three kinds of grain shape that can be distinguished according to grain growth mechanism: (1) solid phase crystallization (SPC), (2) partial melting growth (PMG), and (3) full melting growth (FMG). These three growth mechanisms are as a result of different laser irradiation time to a-Si and relative absorbed laser energy difference, therefore, they achieve different grain size and crystallinity. By using this blue laser annealing (BLA) system, we can obtain the high performance and low cost low temperature polycrystalline silicon (LTPS) TFTs with large grain size.

Fluorescence imaging for photodynamic therapy of non-melanoma skin malignancies – A retrospective clinical study

Abstract Background and objective: Photodynamic therapy (PDT) has been successfully used in clinical practice for decades; however, clinical outcome data are not always consistent resulting in a great necessity for real-time monitoring to predict the therapy outcome. Study design and methods: In a retrospective clinical study, 402 patients with non-melanoma skin malignancies were enrolled who underwent PDT treatment and fluorescence real-time imaging. The photosensitizer used was a chlorine e6 derivative (Fotoditazin®); the tumors were irradiated with a 662 nm continuous wave diode laser with fiber delivery system and total fluence of up to 300 J/cm2. The fluorescence imaging was performed using a commercially available system with a camera and bandpass filter in the range of 710–800 nm. Fluorescence contrast (FC) of the tumor (the ratio of the average fluorescence intensities in the tumor and the surrounding tissues) and its change during the PDT treatment (photobleaching, dFC) was measured. Then the correlation between the clinical outcome (tumor response and recurrence rate) and measured fluorescence parameters was evaluated. The follow-up period was 6–53 months (median, 28 months). Results: FC or dFC below their median values independently correspond to a significant increase in tumor recurrence rate (p<0.05), and slight increase of partial or no tumor response cases. Tumor response is better correlated with the value of FC, and not correlated with the photobleaching. Conclusion: Baseline FC and its change after PDT treatment may serve as a predictor of recurrence. This finding is a step towards individualized PDT cancer treatment.

Sub-micron scale patterning of fluorescent silver nanoclusters using low-power laser.

Noble metal nanoclusters are ultrasmall nanomaterials with tunable properties and huge application potential; however, retaining their enhanced functionality is difficult as they readily lose their properties without stabilization. Here, we demonstrate a facile synthesis of highly photostable silver nanoclusters in a polymer thin film using visible light photoreduction. Furthermore, the different stages of the nanocluster formation are investigated in detail using absorption and fluorescence spectroscopy, fluorescence microscopy, and atomic force microscopy. A cost-effective fabrication of photostable micron-sized fluorescent silver nanocluster barcode is demonstrated in silver-impregnated polymer films using a low-power continuous-wave laser diode. It is shown that a laser power of as low as 0.75 mW is enough to write fluorescent structures, corresponding to the specifications of a commercially available laser pointer. The as-formed nanocluster-containing microstructures can be useful in direct labeling applications such as authenticity marking and fluorescent labeling.

Lateral Grain Growth of Amorphous Silicon Films With Wide Thickness Range by Blue Laser Annealing and Application to High Performance Poly-Si TFTs

We report high performance p-type poly-Si thin-film transistors (TFTs) achieved by lateral grain growth of amorphous silicon (a-Si) by using a continuous-wave blue diode laser of wavelength 445 nm. The blue laser beam is efficiently absorbed into the a-Si film, such that full melting and lateral crystallization is achieved in all thicknesses investigated, 50-200 nm. TFTs fabricated with 75-, 100-, and 125-nm-thick poly-Si films laterally grown by the blue laser annealing exhibited field-effect mobility of 108 ± 7, 104 ± 9, and 134 ± 12 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /V · s, and subthreshold swing of 210±51, 191±16, and 193±53 mV/decade, respectively, and high ON/OFF current ratio of ~10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</sup> .

Background-free Brillouin spectroscopy in scattering media at 780 nm via stimulated Brillouin scattering.

We demonstrate the effectiveness of stimulated Brillouin scattering for background-free Brillouin spectroscopy in scattering media within the biological spectral window. Using two nearly counter-propagating continuous-wave diode laser beams at 780 nm, we acquired transmission stimulated Brillouin point spectra in 10 mm and 500 μm thick Intralipid tissue phantoms with ∼100 μm and ∼16 μm diameter focal points, respectively. Stimulated gain spectra with high signal-to-noise ratio (8.7-30.7 dB) and frequency accuracy (6-72 MHz) were obtained at 20 MHz/10 ms and 20 MHz/100 ms through 0.24-3.36 mean-free paths of tissue phantoms. Our results suggest that stimulated Brillouin gain can be useful for imaging of Brillouin resonances in submillimeter-thick scattering samples.

Exact and near backscattering measurements of the linear depolarisation ratio of various ice crystal habits generated in a laboratory cloud chamber

Ice clouds were generated in the Manchester Ice Cloud Chamber (MICC), and the backscattering linear depolarisation ratio, δ, was measured for a variety of habits. To create an assortment of particle morphologies, the humidity in the chamber was varied throughout each experiment, resulting in a range of habits from the pristine to the complex. This technique was repeated at three temperatures: −7°C, −15°C and −30°C, in order to produce both solid and hollow columns, plates, sectored plates and dendrites. A linearly polarised 532nm continuous wave diode laser was directed through a section of the cloud using a non-polarising 50:50 beam splitter. Measurements of the scattered light were taken at 178°, 179° and 180°, using a Glan–Taylor prism to separate the co- and cross-polarised components. The intensities of these components were measured using two amplified photodetectors and the ratio of the cross- to co-polarised intensities was measured to find the linear depolarisation ratio. In general, it was found that Ray Tracing over-predicts the linear depolarisation ratio. However, by creating more accurate particle models which better represent the internal structure of ice particles, discrepancies between measured and modelled results (based on Ray Tracing) were reduced.

Correlation of the crystal orientation and electrical properties of silicon thin films on glass crystallized by line focus diode laser

In this work, crystallographic orientation of polycrystalline silicon films on glass formed by continuous wave diode laser crystallization was studied. Most of the grain boundaries were coincidence lattice Σ3 twin boundaries and other types of boundaries such as, Σ6, Σ9, and Σ21 were also frequently observed. The highest photoluminescence signal and mobility were observed for a grain with (100) orientation in the normal direction. X-ray diffraction results showed the highest occupancies between 41 and 70% along the (110) orientation. However, the highest occupancies changed to (100) orientation when a 100nm thick SiOx capping layer was applied. Suns-Voc measurement and photoluminescence showed that higher solar cell performance is obtained from the cell crystallized with the capping layer, which is suspected from increased occupancies of (100) orientation.

Second-order interference of two independent and tunable single-mode continuous-wave lasers**Project supported by the National Natural Science Foundation of China (Grant No. 11404255) and the Doctor Foundation of Education Ministry of China (Grant No. 20130201120013).

The second-order temporal interference of two independent single-mode continuous-wave lasers is discussed by employing two-photon interference in Feynman’s path integral theory. It is concluded that whether the second-order temporal interference pattern can or cannot be retrieved via two-photon coincidence counting rate is dependent on the resolution time of the detection system and the frequency difference between these two lasers. Two identical and tunable single-mode continuous-wave diode lasers are employed to verify the predictions. These studies are helpful to understand the physics of two-photon interference with photons of different spectra.

Photoinduced Kondo effect inCeZn3P3

The Kondo effect, which originates from the screening of a localized magnetic moment by a spin-spin interaction, is widely observed in nonartificial magnetic materials, artificial quantum dots, and carbon nanotubes. In devices based on quantum dots or carbon nanotubes that target quantum information applications, the Kondo effect can be tuned by a gate voltage, a magnetic field, or light. However, the manipulation of the Kondo effect in nonartificial materials has not been thoroughly studied; in particular, the artificial creation of the Kondo effect remains unexplored. Per this subject study, however, a route for the optical creation of the Kondo effect in the nonartificial material $p$-type semiconductor ${\mathrm{CeZn}}_{3}{\mathrm{P}}_{3}$ is presented. The Kondo effect emerges under visible-light illumination of the material by a continuous-wave laser diode and is ultimately revealed by photoinduced electrical resistivity, which clearly exhibits a logarithmic temperature dependency. By contrast, a La-based compound (${\mathrm{LaZn}}_{3}{\mathrm{P}}_{3}$) displays only normal metallic behavior under similar illumination. The photoinduced Kondo effect, which occurs at higher temperatures when compared with the Kondo effect in artificial systems, provides a potential range of operation for not only quantum information/computation devices but also for operation of magneto-optic devices, thereby expanding the range of device applications based on the Kondo effect.

Realistic Instrumentation Platform for Active and Passive Optical Remote Sensing.

We describe the development of a novel versatile optical platform for active and passive remote sensing of environmental parameters. Applications include assessment of vegetation status and water quality. The system is also adapted for ecological studies, such as identification of flying insects including agricultural pests. The system is based on two mid-size amateur astronomy telescopes, continuous-wave diode lasers at different wavelengths ranging from violet to the near infrared, and detector facilities including quadrant photodiodes, two-dimensional and line scan charge-coupled device cameras, and a compact digital spectrometer. Application examples include remote Ramanlaser-induced fluorescence monitoring of water quality at 120 m distance, and insect identification at kilometer ranges using the recorded wing beat frequency and its spectrum of overtones. Because of the low cost this developmental platform is very suitable for advanced research projects in developing countries and has, in fact, been multiplied during hands-on workshops and is now being used by a number of groups at African universities.