Akihiro Utsumi

Impact of pulsed Nd:YAG laser irradiation on the growth and mortality of the biofilm forming marine bacterium Pseudoalteromonas carrageenovora

The impact of pulsed laser irradiation on the marine biofilm forming bacterium Pseudoalteromonas carrageenovora was investigated in the laboratory by monitoring mortality and the post-irradiation growth pattern. The impact of laser irradiation on bacterial mortality increased with the duration of irradiation. Laser irradiation at 532 nm (0.1 J cm m 2 ) for 15 min resulted in a 53% cell mortality immediately after irradiation. However, the impact after a period of 5 h (delayed impact) was more severe. The growth pattern of irradiated samples showed a prolonged lag phase compared to the reference, due to a reduction in total viable counts (TVC) in the irradiated samples. Nucleic acid staining is suggested to be a promising technique for monitoring laser inflicted bacterial mortality. Thus, the results suggest that laser irradiation could be considered as an alternative technique to reduce the number of biofilm forming bacteria and thereby biofilm formation on hard surfaces.

Pulsed laser irradiation impact on two marine diatoms Skeletonema costatum and Chaetoceros gracilis

The ability of pulsed laser irradiations to cause damage on the biofouling organisms is recently being investigated. If this technique is employed in industries such as power generation wherein a large quantity of water is being used for the cooling purpose, many organisms other than the targeted would get affected. In this study, we have investigated the damage caused by the pulsed laser irradiations from an Nd:YAG laser (fluence 0.1J/cm(2)) for varying durations such as 2, 5, 10, 30, 60 and 300 s on two marine diatom species namely Skeletonema costatum and Chaetoceros gracilis. Upon exposure to low power laser irradiations, these diatom species showed mortalities between 52.6+/-9.3% to 97.7+/-3.1% in the case of S. costatum and 57.8+/-2.5% to 98.9+/-0.6% in the case of C. gracilis for 2 and 300 s of irradiations, respectively. The mortality increased with the increase in the duration of laser irradiation. The estimation of the chlorophyll a concentration in the irradiated samples showed a considerable reduction varying between 9.8% and 57% in C. gracilis and 3% and 70.3% in S. costatum for 2 and 300 s of irradiations, respectively. The laser-survived cells grew as the non-irradiated (control) samples. C. gracilis frustules were broken by the laser whilst, the cell materials were drained out of the frustules in the case of S. costatum. The study therefore showed that the low power pulsed laser irradiations could cause significant damage on the two species of planktonic diatoms.

Molecular level damages of low power pulsed laser radiation in a marine bacterium Pseudoalteromonas carrageenovora

Aim:u2002 To study the molecular level damages in a marine bacterium, Pseudoalteromonas carrageenovora, exposed to low power pulsed laser radiation from an Nd:YAG laser.

Impact of Pulsed Laser Irradiations from Nd:YAG Laser on the Larvae of the Fouling Barnacle Balanus amphitrite

The environmental hazards originating from the persistent use of antifouling agents containing toxic chemicals are alarming. Therefore, methods that do not rely on toxic elements are wanted. The effectiveness of pulsed laser irradiations from an Nd:YAG laser to induce damage to the larvae of a fouling barnacle, Balanus amphitrite, was evaluated in the laboratory. The average fluence tested was 0.1 J cmm 2. Three larval stages, viz. nauplii stage II and stage IV and cyprid larvae were exposed to laser irradiations for 2 s, 10 s, 30 s, 1 min, 5 min and 15 min in the case of nauplii stage II, and 2, 10 and 30 s in case of nauplii stage IV and cyprid larvae. Mortality occurred immediately after, as well as 1 and 3 d after the irradiation, and the settlement rate of cyprid larvae was investigated in the laboratory. Mortality in stage II, stage IV and cyprid larvae immediately after 2 s irradiation was 30.1 ± 0.5%, 9.3 ± 0.2 and 16.7 ± 4.8, respectively. Mortality after 3 d however showed higher values, viz. 84.4 ± 6.7%, 50 ± 4%, and 75 ± 9.4 in stage II, stage IV and cyprid larvae, respectively. Mortality increased with the period of laser irradiation. The stage II nauplii showed 100% mortality after 10 s irradiation. The mortality observed in stage IV and cyprid larvae was less than that found for the stage II nauplii. The IV stage larvae which survived could successfully moult to the next stage, whilst the irradiated cyprid larvae could not settle. The results thus showed that pulsed low power laser irradiations could cause significant damage to the larvae of this common fouling barnacle.

Lethal and sub‐lethal impacts of pulsed laser irradiations on the larvae of the fouling barnacle Balanus amphitrite

Laboratory experiments were conducted to study the impact of laser irradiation on the larvae of the fouling barnacle Balanus amphitrite. Research pertaining to fouling invertebrate larvae‐laser interaction is sparse and, hence, data on this aspect were thought significant in order to consider pulsed low power laser irradiations as a possible future antifouling tool. Lethal and sub‐lethal impacts of four very low laser fluences, viz. 0.013, 0.025, 0.05 and 0.1 J cm‐2 for three different durations, viz. 2, 10 and 30 s were investigated. Three growth stages of barnacle larvae, viz. nauplii stage II, nauplii stage IV and cyprids were exposed to the mentioned laser fluences for different durations. While lethal impact was assessed immediately after and 1 d after irradiation, sub‐lethal impacts were studied by monitoring the success rate of the irradiated nauplii in reaching the cyprid stage. In addition, the swimming speed of VIth stage nauplii after irradiation was studied. In the case of cyprids, in addition to the mortality measurement immediately after and 1 d after irradiation, the settlement rate was investigated. In all the above experiments, non‐irradiated larvae served as controls. The results showed an increase in mortality with increasing laser fluence and duration of irradiation. Irradiation for 2 s resulted in significant mortality in nauplii, while it was less in the case of cyprids. In IInd stage nauplii, the mortality immediately after irradiation for 2 s varied from 14.8±2.12 to 97.1±4.1% for laser fluences of 0.013 and 0.1 J cm‐2, respectively. However, in cyprids, the mortality immediately after irradiation for 2 s varied from 12.2±3 to 13.4±1.2% for fluences of 0.013 and 0.1 J cm‐2, respectively. The mortality in IVth stage nauplii was less than that for IInd stage nauplii but more than that for cyprids. There was a significant increase in mortality with time after irradiation. The formation of cyprids from the irradiated larvae was significantly less than that observed for non‐irradiated larvae. Also, the irradiated larvae showed a significantly slower swimming speed compared to the control samples. The settlement rate in cyprids was reduced significantly by the laser irradiation. This was true even for the lowest fluence and shortest period of irradiation tested. Thus, the results of the experiment showed that even a low power pulsed laser irradiation of 0.013 J cm‐2 for 2 s can cause significant damage to fouling barnacle larvae.

Laser Impact on Bacterial ATP: Insights into the Mechanism of Laser-Bacteria Interactions

The mechanisms of laser action on bacteria are not adequately understood. Here, an attempt has been made to study the fluctuation in ATP (adenosine triphosphate) concentration following laser irradiation from a pulsed Nd:YAG laser on a marine biofilm-forming bacterium Pseudoalteromonas carrageenovora. A stationary phase bacterial suspension (density 107-8 mlm 1) was exposed to pulsed laser irradiations at a fluence of 0.1 J cmm 2 (pulse width 5 ns, repetition rate 10 Hz) for different durations, ranging from 2 s to 15 min. The total viable count (TVC) and ATP concentration of the irradiated samples were determined immediately after the laser irradiation. While the maximum reduction in the TVC observed with respect to the control was 59% immediately after 15 min irradiation, the ATP concentration showed a reduction of about 86% for the same duration. The ATP concentration showed an abrupt reduction from 3 min of laser irradiation and continued to reduce significantly with increasing duration of irradiation. Thus, 3 min irradiation at a fluence of 0.1 J cmm 2 is considered as an approximate threshold for ATP production in this bacterium. As the decreased level of ATP production continued, bacterial mortality resulted. The reduction in ATP production could be due to damage caused by the laser irradiations on bacterial metabolic processes such as cellular respiration.

Laser damage to marine plankton and its application to checking biofouling and invasion by aquatic species: a laboratory study

In this laboratory study, the ability of low-power pulsed laser irradiation to kill planktonic organisms in a flowing water system was examined, thus, to test the possibility of using this technique as a water treatment strategy to reduce biofouling growth in condenser tubes of power plants and to reduce bioinvasion via the ballast water of ships. Two flow rates (4.6 and 9.0 l h−1) were tested on three planktonic organisms: two marine centric diatoms viz. Skeletonema costatum and Chaetoceros gracilis and a dinoflagellate, Heterocapsa circularisquama. A low-power pulsed laser irradiation at 532 nm with a fluence of 0.1 J cm−2 from a frequency-doubled Nd:YAG laser was used as the irradiation source. The laser irradiation resulted in a heavy mortality of the test cells. The mortality observed was >90% for S. costatum and H. circularisqama and >70% for C. gracilis. The results suggest that laser irradiation has the potential to act as a water treatment strategy to reduce biofouling of condenser tubes in power plants as well as to reduce species invasion via the ballast water of ships.

Laser Impact on Marine Planktonic Diatoms: An Experimental Study Using a Flow Cytometry System

A flow cytometry system was used to evaluate the impact of pulsed laser irradiations from an Nd:YAG laser on two marine coastal water diatoms, Chaetoceros gracilis and Skeletonema costatum. Three flow speeds, i.e. 9, 18 and 27 ml minm 1 and three laser fluences, i.e. 0.025, 0.05 and 0.1 J cmm 2 pulsem 1 were tested during this study. The reduction in cell density and chlorophyll a (chl a) concentrations were monitored by reference to non-irradiated samples as controls. Upon irradiation, the cell density and the chl a concentrations became reduced significantly compared to the control (one way ANOVA p <0.001 for the cell density in both the species and p <0.05 for chl a concentrations in both species). A maximum mortality of 0.77 log10 (about 83%) for C. gracilis and 0.68 log10 (about 78%) for S. costatum was observed at 9 ml minm 1 flow speed and 0.1 J cmm 2 laser fluence. The maximum reduction observed in the chl a concentration was about 26% (control 0.413 and sample 0.306 mg mlm 1) for C. gracilis and 27% (control 0.222 and sample 0.16 mg mlm 1) for S. costatum, when the flow rate was 9 ml minm 1 and the fluence 0.1 J cmm 2. In general, mortality increased with an increase in the laser fluence. The results thus show if the cooling water is laser-irradiated to mitigate biofouling, this could result in significant damage to the planktonic flora of the flowing seawater system, which in turn might reduce algal biofilm formation on industrially important structures. The reduction in the chl a concentration showed that the laser irradiations also could result in a significant reduction in the primary productivity of the cooling water.

Effect of laser power on clad metal in laser-TIG combined metal cladding

TIG arc welding has been used to date as a method for clad welding of white metal as bearing material. We propose a new clad welding process that combines a CO2 laser and a TIG arc, as a method for cladding at high speed. We hypothesized that this method would permit appropriate control of the melted quantity of base metal by varying the laser power. We carried out cladding while varying the laser power, and investigated the structure near the boundary between the clad layer and the base metal. Using the laser-TIG combined cladding, we found we were able to control appropriately the degree of dilution with the base metal. By applying this result to subsequent cladding, we were able to obtain a clad layer of high quality, which was slightly diluted with the base metal.

Nd:YAG laser welding of aluminum alloy assisted by high-peak pulsed lasers

Nd:YAG laser welding of an aluminum alloy assisted by high-peak pulsed lasers such as excimer and Q-switched Nd:YAG laseers was investigated. In this novel laser hybrid welding, a plasma induced by a high-peak power laser absorbs the Nd:YAG laser energy and transmits it to a work piece. In the laser welding of the aluminum alloy using the Nd:YAG laser of which maximu power was 6 kW, the heat input and the penetration depth increased by 20% and 8%, respectively, by using simultaneous irradiation of the excimer laser of which average power was only 16 W. According to the optical emission of the plasmas, not only KrF excimer laser but also 2nd harmonic of a Q-switched Nd:YAG laser is applicable for the laser hybrid welding as the high-peak pulsed laser.