Continuous Wave Blue Light Research Articles

Use of optically stimulated luminescence (OSL) in the detection of irradiated spices.

In this study, the validity of using the optically stimulated luminescence (OSL) technique as a scanning method for the detection of irradiated foodstuffs was investigated. Gamma-irradiated thyme, mint and clove samples were stimulated with a continuous wave blue light (CW-OSL) and their OSL signal sensitivity and stability properties were measured. While no OSL signal was observed for all non-irradiated spices, a significant increase in the intensity of OSL signals was noted for all samples after irradiation with 5kGy, 10kGy and 20kGy. It was also observed that the measured OSL signals were well above the background level even after one year of irradiation. It is therefore concluded that irradiated thyme, mint and clove samples can clearly be identified using the CW-OSL technique without any pre-treatment even one year after irradiation. This result indicates that, where spices contain sufficient silicate minerals, the CW-OSL technique could be used as a method for detecting irradiation.

Pulsed 450 nm blue light significantly inactivates Propionibacterium acnes more than continuous wave blue light

Infection with Propionibacterium acnes is ubiquitous, and drug resistant strains have been on the rise as the use of pharmaceutical antimicrobials continues to engender the emergence of further resistant strains. In previous studies, we showed that treatment with blue light serves as an alternative to pharmaceutical intervention. As a part of our ongoing effort to improve the antimicrobial efficacy of blue light, we studied the effect of pulsed 450 nm light on P. acnes in vitro and compared two pulsed rates with continuous wave irradiation. We irradiated cultures of P. acnes at various irradiances and radiant energies either singly or repeatedly at various time intervals, using printed micro-LEDs, with the goal of finding the lowest combination of irradiance and radiant energy that would yield 100% bacterial suppression. Our results show that treatment with 33% pulsed light gave the best result compared to 20% pulsed wave or continuous wave. Timing irradiation to coincide with the replication cycle of P. acnes produced a significantly better antimicrobial effect. Furthermore, repeated irradiation at 3-h or 4-h interval enabled significant bacterial suppression even at lower irradiances; thus, making single irradiation at high irradiances unnecessary. Moreover, combining repeated irradiation with appropriate duration of treatment and 33% irradiation pulse rate gave optimal 100% [7 log10] bacterial suppression.

Pulsed 450 nm blue light suppresses MRSA and Propionibacterium acnes in planktonic cultures and bacterial biofilms

In our recent study, we showed that pulsed blue light (PBL) suppresses the growth of Propionibacterium acnes more than continuous wave (CW) blue light in vitro, but it is not known that other bacteria, such as methicillin-resistant Staphylococcus aureus (MRSA), respond similarly to PBL. The high potency of PBL relative to CW blue light makes it a suitable antimicrobial for suppressing bacterial growth in biofilms as well. Therefore, we determined if MRSA—a deadly bacterium of global concern—is susceptible to 450 nm PBL irradiation in vitro, and ascertained whether the bactericidal effect of PBL on planktonic P. acnes culture can be replicated in biofilms of P. acnes and MRSA. In three series of experiments, we irradiated P. acnes and MRSA respectively, either in planktonic cultures, forming biofilms or formed biofilms. Compared to controls, the results showed 100% bacterial suppression in planktonic cultures of MRSA irradiated with 3 mW/cm2 irradiance and 7.6 J/cm2 radiant exposure three times at 30-minute intervals, and also in P. acnes cultures irradiated with 2 mW/cm2 irradiance 5 J/cm2 radiant exposure thrice daily during each of 3 days. Irradiation of biofilms with the same irradiances and radiant exposures that gave 100% bacterial suppression in planktonic cultures resulted in disruption and disassembly of the architecture of MRSA and P. acnes biofilms, more so in forming biofilms than formed biofilms. The antimicrobial effect on each bacterium was minimal in forming biofilms, and even less in formed biofilms. Increasing radiant exposure slightly from 7.6 J/cm2 to 10.8 J/cm2 without changing any other parameter, yielded more disruption of the biofilm and fewer live MRSA and P. acnes, suggesting that 100% bacterial suppression is possible with further refinement of the protocol. In both planktonic cultures and biofilms, PBL suppressed MRSA more than P. acnes.

Intracavity sum-frequency generation of CW blue light in Nd:LuVO4 laser

We report for the first time a continuous-wave (CW) blue laser emission by sum-frequency mixing in Nd:LuVO4 crystal. Using type-I critical phase-matching (CPM) LBO crystal, a blue laser at 493 nm is obtained by 1066 and 916 nm intracavity sum-frequency mixing. The maximum laser output power of 520 mW is obtained when an incident pump laser of 18.2 W is used. At the output power level of 520 mW, the output stability is better than 2.8%. The beam quality M2 value is are about 1.22 and 1.31 in both horizontal and vertical dimensions respectively.

All-solid-state continuous wave intracavity frequency-tripled Nd:YVO4–LiB3O4 blue laser using double-resonant approach

In the paper, a new way of intracavity frequency-tripled all-solid-state laser to generate continuous wave blue coherent radiation is firstly demonstrated. High-efficiency of continuous wave third harmonic generation using the approach of double-resonance at fundamental frequency and second harmonic is developed by insertion of one wedge prism for the phase control. The maximum output power at the wavelength of 447nm, which was generated with two long LiB3O4 crystals by noncritical phase matching, is about 1.15W with a beam quality factor of M2 of 1.05. From the experimental results, the generation of continuous wave blue light using this way with higher conversion efficiency can be achieved.

Generation of 2.1 W Continuous Wave Blue Light by IntracavityDoubling of a Diode-End-Pumped Nd:YAG Laser in a 30 mm LBO

A folded four-mirror cavity with a composite Nd:YAG rod is optimized toobtain high efficient cw 473 nm blue output. The laser could operatestably in the region of the thermal-lens focal length from 20 mm to70 mm. LBO is used for intracavity frequency doubling of the 946 nmtransition of Nd:YAG and the optimum LBO length is investigated. Amaximum output power of 2.1 W in the blue spectral range at 473 nm isachieved with 30-mm-long LBO, corresponding to an optical conversionefficiency of 9.1%.

Do pulsed lasers produce an effective photodynamic therapy response?

Photodynamic therapy (PDT) in dermatology is traditionally performed with topical aminolevulinic acid (ALA) and continuous-wave (CW) illumination with blue or red light. Recently, several authors have reported success with laser and other pulsed-light sources for PDT. While the clinical benefits on sun-exposed skin are apparent, no study has demonstrated that the pulsed light sources are responsible for the observed response. A placebo-controlled study of two pulsed light sources previously reported for PDT: the pulsed dye laser (PDL) or broadband flashlamp filtered intense pulsed light (IPL). Sun-hidden skin was prepared with microdermabrasion and acetone scrub followed by ALA under occlusion. Laser or IPL was delivered under conditions previously reported to produce a clinical response. Control areas were exposed to standardized CW blue light or to no light. A second control area was prepared and received light and the ALA vehicle. IPL and PDL demonstrated a faint dose-response effect on PDT activation, but were less potent than a smaller fluence of CW blue light. Ambient light activated ALA-treated skin. Both IPL and PDL are capable of activation of PDT but produce dramatically less PDT reaction than the standard CW blue-light broadband source. Physicians desiring a robust PDT response might select CW sources over pulsed sources. Ambient light may activate a PDT reaction.

Efficient continuous wave blue light generation in optical superlattice LiNbO3 by direct frequency doubling a 978 nm InGaAs diode laser

First-order quasiphase matched blue light generation in a LiNbO3 optical superlattice was performed by direct frequency doubling of a continuous wave 978-nm diode laser. 1.27 mW output power of blue light was obtained with an incidence power of 500 mW. The frequency conversion efficiency is 0.25%.

High power continuous wave blue light generation in KNbO3 using semiconductor amplifier seeded by a laser diode

Diffraction limited emission of a GaAlAs tapered amplifier seeded by a laser diode is frequency doubled in a 12.4-mm-long KNbO3 crystal to generate 62 mW of 429 nm continuous wave emission, corresponding to a conversion efficiency of 1.1%/W cm. Reductions in the conversion efficiency due to nonuniform temperature distribution caused by blue-enhanced infrared absorption were characterized.