Laser Time Research Articles

Maxwell–Bloch Equation Approach for Describing the Microscopic Dynamics of Quantum-Dot Surface-Emitting Structures

We present a theoretical investigation of the optical properties of an electrically pumped surface-emitting structure composed of quantum dot (QD) layers as active medium and Bragg reflectors. The electric field propagation and the carrier dynamics of QDs embedded into a 2-D wetting layer (WL) are calculated using QD-WL Maxwell-Bloch equations. The equations are evaluated using the finite-difference time-domain (FDTD) method. To provide a detailed understanding of the carrier dynamics, microscopically calculated Coulomb scattering rates as well as the dephasing time are incorporated into the equations. The approach is applied to investigate the normal mode coupling as a function of the WL carrier densities. The mode splitting only appears at small WL carrier densities within strong coupling regime where Coulomb scattering is of minor importance. The transmission is studied as a function of the pump pulse intensity. At high intensities, saturation or inversion of the optically active QD levels is reached resulting in an enhanced transmission. Furthermore, the switch-on dynamics of the vertical cavity surface-emitting laser (VCSEL) with a time-dependent injection current is calculated. It is shown to be characterized by strongly damped electric field. We find a characteristic lasing delay time accounting for the time charge carriers need to scatter from bulk WL states into QD states and to relax radiatively.

Effects of different application durations of ER:YAG laser on intrapulpal temperature change during debonding

This study was done to determine the amount of lasing time required to remove ceramic brackets safely without causing intrapulpal damage by using Er:YAG laser with the scanning method. Part 1: 80 bovine mandibular incisors with ceramic brackets were randomly assigned into four groups of 20 as one control and three study groups. In the study groups, brackets were debonded after lasing for 3, 6, and 9 s, whereas debonding was performed without lasing in the control group. Shear bond strengths and ARI scores were also measured. Part 2: 30 human premolars with ceramic brackets were randomly divided into three groups of ten, as 3, 6, and 9s of lasing durations. Intrapulpal temperature was measured at the same lasing times by a thermocouple. Statistically significant lower shear bond strengths were found in study groups compared to the control. A negative correlation was seen between the bond strengths and ARI scores in such a way that, as the shear bond strengths decreased, the ARI scores increased. Temperature increases for all the study groups were measured below the 5.5°C benchmark. All lasing times were effective for debonding without causing enamel tear outs or bracket failures. The temperature proportionally increased with the extension of the lasing duration. Six-second lasing by the scanning method using Er:YAG laser was found to be the most effective and safest way of removing the ceramic brackets without causing damage to the enamel and pulpal tissues.

Endonasal Laser Tissue Welding: First Human Experience

Adequate repair of cerebrospinal fluid leak remains a significant challenge in endoscopic skull base surgery. Laser tissue welding (LTW) is a method of creating an instant watertight wound closure using a chromophore doped biological solder, which may be used for cranial base reconstruction. The objective of this study is to assess the safety and technical feasibility of endoscopic LTW in human sinonasal mucosa. A prospective, Institutional Review Board-approved study was performed of 10 patients undergoing endoscopic LTW using an albumin and hyaluronic acid-based solder for repair of mucosal injuries. Data were collected on patient demographics, total lasing time, and volume of solder used. Wounds were prospectively followed by endoscopic exam and scored on a scale of zero to two by three blinded observers (B.S.B., J.N.P., and A.G.C.) for inflammation, thermal injury, and edema. Results were compared with control wounds using the Mann-Whitney U test. Ten patients (seven men and three women; average age 50 years; range, 33-71 years) underwent endoscopic LTW. Total lasing time was 11 +/- 11 minutes requiring 0.96 +/- 0.83 mL of solder per patient. Patients were followed for an average of 72 days (range, 12-138 days) and no complications were noted. Solder persisted for up to 26 days and there was no significant difference between the lased and control wounds with regard to inflammation (0.87 +/- 0.72 versus 1.31 +/- 0.87), thermal injury (0.06 +/- 0.25 versus 0.12 +/- 0.34), or edema scores (1.13 +/- 0.81 versus 1.44 +/- 0.73). Endoscopic LTW is a technically feasible and rapid method of wound closure in sinonasal mucosa that does not result in any significant thermal or inflammatory sequelae.

Analysis of lasing threshold of a nuclear-pumped gas laser depending on the lasing medium residence time in the laser module case

It is shown experimentally that an increase in the lasing mixture residence time in the case of a laser module over 60–120 min prior to an experiment elevates the lasing threshold and deteriorates the energy parameter of the laser. The worsening of the energy parameters of the laser may be due to accumulation of impurity gases. It is shown that the presence of impurities affects the working characteristics of the laser media under investigation to various extents.

The Efficacy and Safety of KTP Photoselective Vaporization of the Prostate for the Treatment of Benign Prostatic Hyperplasia: The 2-year Results

Purpose: This study was conducted to evaluate, with using the 2-year follow-up data, the clinical efficacy and safety of performing photoselective vaporization of the prostate (PVP) for the treatment of symptomatic benign prostatic hyperplasia (BPH). Materials and Methods: We analyzed the clinical data of 104 men with symptomatic BPH and who had undergone PVP. The efficacy parameters were the changes from baseline of the International Prostate Symptom Score (IPSS), the quality of life (QoL) score, the maximum urinary flow rate (Qmax) and the postvoid residual volume (PVR). The patients were evaluated preoperatively and then at post-operative 1, 3, 6, 12 and 24 months. Their complications were also evaluated. Results: The mean prostate volume was 45.6ml. The mean lasing time was 44.9 minutes and there was no significant blood loss or fluid absorption during or immediately after PVP. Significant improvements in the IPSS, the QoL score, the Qmax and the PVR were noted as early as 1 month after PVP treatment. After 24-month follow-up, the mean IPSS decreased from 22.4 to 9.9 (p<0.0001) and the QoL score decreased from 4.4 to 2.3 (p<0.0001), while the mean Qmax changed from 8.3 to 14.4ml/sec (p< 0.0001). The PVR decreased from 82.0 to 49.9ml (p=0.033). The complications were retrograde ejaculation (26.9%), transient catheterization (6.7%), transient dysuria (2.9%), bladder neck contracture (1.9%), urethral stricture (0.9%) and meatal stenosis (0.9%). 1 patient was diagnosed with prostate cancer 32 months after operation. Conclusions: Significant improvements of the subjective and objective voiding parameters were achieved and these were sustainable for at least 2-year, with minimal complications, after PVP. PVP seems to be a safe and effective treatment for symptomatic BPH. (Korean J Urol 2008;49: 831-836) 󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏

A New Discharge Scheme of a Prepulse Plus Two Main Pulses forCapillary-Discharge Soft-X-Ray Laser

Reducing the capillary-discharge current is one way of possiblydecreasing the pumping power requirement. We examine the influence ofvarious discharge currents on laser intensity and determine thesuitable pre-discharge condition for a 46.9-nm discharge-pumped Ne-likeAr soft-x-ray amplifier. The experimental results show that a highadditional pre-pulse current at amplitude of several kA and with a veryshort duration of several tens of nanosecond can effectively decreasethe amplitude of the main discharge current at the lasing time. Wepropose a new discharge scheme of a pre-pulse plus two main pulseswhich appears to significantly decrease the requirement for dischargecurrent. This in turn may decrease the pumping power requirement forthe capillary discharge laser and can greatly increase laserefficiency.

PHOTOSELECTIVE POTASSIUM-TITANYL-PHOSPHATE LASER VAPORIZATION OF THE BENIGN OBSTRUCTIVE PROSTATE: OBSERVATIONS ON LONG-TERM OUTCOMES

We present long-term observations on photoselective vaporization of the prostate in a prospectively studied cohort of men with obstructive benign prostatic hyperplasia. Obstructive benign prostatic hyperplasia in 94 men was treated with transurethral near contact vaporization with potassium-titanyl-phosphate laser with the patient under general or spinal anesthesia. Baseline characteristics, perioperative data, postoperative outcomes and adverse events were recorded. Mean prostate volume was 45 ml (range 13 to 136). Mean lasing time was 47 minutes (range 10 to 99), and there was minimal blood loss and no evidence of fluid absorption. All 94 men were outpatients and all but 1 became catheter-free in less than 24 hours. Baseline mean American Urological Association symptom index score was 22, quality of life score 4.5, peak urinary flow rate 7.8 ml per second and post-void residual urine volume 197 ml. After surgery percentage changes from baseline in mean values of these parameters, reflecting significant (p <0.0001) improvement at 1, 2, 3 and 5 years, ranged from 83% to 88%, 86% to 90%, 170% to 252% and 76% to 89%, respectively. Complications were mild, and included transient dysuria (6%), delayed hematuria (3%), bladder neck contracture (2%) and 2-day retention (1%). No patient had incontinence or newly developed impotence, but up to 26% of the sexually active men experienced retrograde ejaculation. Postoperatively, low stage prostate cancer was detected in 5% of the patients. : Despite limitations our long-term experience and the literature suggest that significant improvements in symptomatic and urodynamic outcomes of photo-selective vaporization of the prostate are achievable and sustainable.

POTASSIUM-TITANYL-PHOSPHATE LASER LAPAROSCOPIC PARTIAL NEPHRECTOMY WITHOUT HILAR CLAMPING IN THE SURVIVAL CALF MODEL

Laparoscopic partial nephrectomy (LPN) with hilar clamping represents the various challenges associated with warm ischemia. We tested the feasibility, and acute and chronic outcomes of LPN using a potassium-titanyl-phosphate (KTP) laser without vascular hilar clamping in the survival calf model. Six Jersey calves weighing 76 to 94 kg underwent a total of 12 staged bilateral transperitoneal laser LPNs of the mid/lower pole using an 80 W KTP laser, including left kidney chronic LPN with 1-month followup in 6 and right kidney acute LPN with immediate sacrifice in 6. Two techniques (ablative vaporization in 5 subjects and wedge resection in 7) were evaluated. Renal parenchymal resection and hemostasis were achieved only with the laser without any adjunctive hemostatic sutures or bioadhesives. Retrograde pyelography, renal arteriography and histological analyses were performed. All 12 procedures were successful performed laparoscopically without open conversion and 11 (92%) were done without hilar clamping. Mean total operative time was 2.9 hours (range 1.5 to 5) and mean blood loss was 119 cc (range 25 to 300). Mean lasing time was 56 minutes (range 20 to 100) with an average energy use of 54 kJ. Mean preoperative and postoperative hemoglobin (10.38 and 10.52 gm/dl) and serum creatinine (0.46 and 0.4 gm/dl, respectively) were similar. At 1-month followup there was no evidence of urinary leakage or arteriovenous fistula. This initial study of laparoscopic KTP laser partial nephrectomy without hilar clamping confirms its technical feasibility in most cases and good short-term outcomes. This success of laser LPN in the robust survival calf model with its human-sized kidney holds promise for future clinical application.

Optical injection probing of single ZnO tetrapod lasers

The properties of zinc oxide (ZnO) nanotetrapod lasers are characterized by a novel ultrafast two-color pump/stimulated emission probe technique. Single legs of tetrapod species are isolated by a microscope objective, pumped by 267 nm pulses, and subjected to a time-delayed 400 nm optical injection pulse, which permits investigation of the ultrafast carrier dynamics in the nanosize materials. With the optical injection pulse included, a large increase in the stimulated emission at 400 nm occurs, which partially depletes the carriers at this wavelength and competes with the normal 390 nm lasing. At the 390 nm lasing wavelengths, the optical injection causes a decrease in the stimulated emission due to the energetic redistribution of the excited carrier depletion, which occurs considerably within the time scale of the subpicosecond duration of the injection pulse. The effects of the optical injection on the spectral gain are employed to probe the lasing dynamics, which shows that the full-width at half-maximum of the lasing time is 3 ps.

The lasing time of soft x-ray laser pumped by capillary discharge

The laser spike of Ne_like argon at 469nm pumped by capillary discharge is mea sured with x_ray diode. Changing the pressure of Ar gas filled in the ceramic ca pillary and the peak value of the main discharge current, we study the effects o f experimental parameters on lasing time, which is the time of spike after the o nset of the main discharge current. The experimental results show that the soft x_ray laser is produced at the rise_time of the main discharge current which is 65%—75% of the peak at the lasing time. The lasing time can be delayed several ns when the pressure increases from 28Pa to 55Pa or the peak of main discharge c urrent decreases. In addition, there is maximum amplitude of the laser spike abo ut 42Pa.

Recent research activities at BFEL laboratory

Beijing free electron laser (BFEL) is a Compton-type mid-infrared FEL facility, with first lasing in 1993. In the past two years, two experimental stations were constructed, and the reliability and stability of BFEL improved much. The lasing time provided to the users was more than 1000 hours, and about 250 samples have been irradiated, many application items concerned. Next, BFEL will be upgraded to be user’s facilities, and other three experimental stations will be furnished. This paper describes the operation, application and upgrade plan of BFEL in details. In addition, the development of several research activities are mentioned.

Numerical Investigation of the Prospects of High Energy Laser in Drilling Oil and Gas Wells

Lasers are expected to provide a less expensive alternative to conventional machining and have found wide spread use in many industries. However, the physical phenomena involved in many laser applications are not fully understood. A better and more quantitative understanding of the physical mechanisms governing these phenomena will diminish the need for extensive trial and error experiments. Most of the theoretical models available in the literature have dealt with quasi-steady material removal using a continuous wave laser. This article presents a numerical model to predict the transient thermal behavior process of rocks under the influence of a pulsed laser. A wide range of parameters were considered in this study, the laser powers were varied from 0.1 to 100 kW and the lasing time was varied between 1 and 100 s. One of the results presented in this article shows that limestones consume less energy per unit volume of material removed as compared to sandstones. A comparison between the findings of this numerical study and published experimental data is also presented and shows a qualitative agreement. Finally, it is shown that numerical modeling can be useful in scaling up laboratory results to field applications.

Status of the Beijing IR Free Electron Laser facilities

Beijing free electron laser (BFEL) is a Compton type mid-infrared FEL facility. By using a thermionic cathode RF gun as an injector, 30 MeV s-band RF linac and two wiggler-optical cavity beam lines generate mid- and far-infrared radiation in the wavelength range of 5-50 µm. BFEL facility possesses the conditions for a user's facility. The running is stable, intensity fluctuation of laser is small, and wavelength adjustment is flexible. The stability test showed that the pulse energy fluctuation is about 1% within 30 minutes, and wavelength fluctuation is less than 0.1%. In this year, the lasing time used for users has reached 1000 hours. More than 250 samples have been studied and many application items have been concerned. Five user's stations will be established. Among them, two key experimental stations; FEL spectrum analysis station, and FEL steady state analysis station, have been constructed. For the purpose of user's applications, special equipments have been provided. Some experimental results of the application items are also presented.

HIGH POWER POTASSIUM-TITANYL-PHOSPHATE LASER VAPORIZATION PROSTATECTOMY

We prospectively studied a cumulative cohort of men with obstructive benign prostatic hyperplasia who underwent potassium-titanyl-phosphate (KTP) laser vaporization prostatectomy to determine the safety and efficacy of this procedure. A total of 55 men with symptomatic bladder outlet obstruction due to benign prostatic hyperplasia were treated with a 60 W. KTP laser produced by a prototype Laserscopedagger generator and delivered through a side-deflecting fiber with a 22Fr continuous flow cystoscope. Sterile water was used for irrigation. The prostatic lobes were vaporized to within capsular fibers. Mean lasing time plus or minus standard deviation was 44 +/- 19 minutes. Mean prostate volume plus or minus standard deviation was 43 +/- 14 ml. No patient had any significant blood loss or fluid absorption, or required blood transfusion. Foley catheters did not require irrigation and were removed less than 24 hours postoperatively. All patients remained satisfied with voiding outcome, which changed significantly (p <0.0001). Mean improvement in American Urological Association symptom score at 3, 6, 12 and 24-month intervals was 75%, 79%, 82% and 82%, respectively. Mean increase in peak flow rate at the same intervals was 250%, 242%, 255% and 278%, respectively. Complications included mild transient dysuria in 7%, bladder neck contracture in 2% and delayed hematuria in 4% of patients. None of the patients required re-catheterization or reoperation, or had incontinence or newly developed impotence. Of the sexually active patients 15% and 9% had retrograde ejaculation at 1 and 2 years, respectively. Our observation in a 2-year period indicates that 60 W. KTP laser vaporization prostatectomy is safe and effective for quickly relieving bladder outlet obstruction with minimal postoperative complications, a high rate of patient satisfaction and, to date, a generally good outcome.

Nonlinear dynamics of the dual-wavelength CO2 laser

Theoretical studies have been made of the nonlinear-dynamic modes of operation of a dual-wavelength CO2 laser with continuous pumping by electric discharge and loss modulation in one of the lasing channels. It is shown that by varying the modulation depth and frequency, it is possible to control, over a fairly wide range, the time and energy parameters of lasing in both channels, going from regular to chaotic modes of operation.

Ocena pogodnosti održavanja vozila specijalne namene

In this work, based on data which are taken from real service for the engine of a particular vehicle, evaluation of the maintainability was carried out using the distribution method of long - lasing time of the procedure of maintenance like the cumulative function of probability. Based on the obtained evaluation the analysis of the Mean Time To Repair (MTTR) was carried out as well as the meeting the Tactical - technical requirements.

Erectile dysfunction following Nd-YAG visual laser-assisted prostatectomy (VLAP)

We investigated if side fire Nd-YAG visual laser prostatectomy (VLAP) causes erectile dysfunction (ED) in patients who were sexually active prior to the procedure. The 36 study patients gave a detailed medical/sexual history: physical examination included bulbo-cavernous reflex (BCR) on rectal examination and routine blood tests. Lasing time, power of the applied laser beam (in watts), coagulation site and energy intensity were recorded. Patients with new onset ED during the one year study period underwent pudendal nerve conduction (PNC), color duplex Doppler ultrasonography, and NPT/RigiScan testing. In 6 out of 36 (16.7%) patients reporting significant post-operative ED, there was a tendency towards higher energy applied and longer lasing time but no correlation between prostate size or the site of energy application. Patients reported loss of night and/or morning erections (n = 5), retrograde ejaculations (n = 2), loss of ejaculate (n = 2), and decreased sensation of orgasm (n = 3). Three had abnormal PNC, duplex Doppler showed abnormal blood supply in four, and all six had abnormal NPT/RigiScan. We believe this is the first demonstration that VLAP may be associated with a high rate of ED and that the lasing time and intensity of applied laser energy may play a role in this outcome.

High-power potassium-titanyl-phosphate (KTP/532) laser vaporization prostatectomy: 24 hours later

Objectives. To study the feasibility and immediate postoperative outcome of vaporization prostatectomy by high-power potassium-titanyl-phosphate (KTP/532) laser in 10 men with bladder outlet obstruction due to benign prostatic hyperplasia (BPH) and to evaluate their clinical and voiding outcome 24 hours postoperatively. Methods. The KTP/532 laser at 60 W was produced by a prototype Laserscope generator and delivered through a side-deflecting fiber with a 22F continuous-flow cystoscope. Sterile water was used for irrigation. The prostatic lobes were readily vaporized to within capsular fibers. The mean lasing time was 29 ± 8 minutes, during which a mean of 104.6 ± 30 kJ of energy was delivered. Results. The prostate volumes ranged from 22 to 60 mL (mean 38.4 ± 9.7). None of the 10 patients had any significant blood loss or any fluid absorption. Foley catheters were removed in less than 24 hours postoperatively. All patients were satisfied with their voiding outcome. The mean peak urine flow rate increased from 8 ± 1.3 mL/s preoperatively to 19.4 ± 8.4 mL/s (142%, P = 0.003266) 24 hours postoperatively. Postvoid residual volumes remained essentially unchanged from their preoperative levels, as expected ( P = 0.767423). One patient had urgency, but none had dysuria, hematuria, or incontinence or required recatheterization. Three patients have returned for 3-month follow-up; all 3 patients have had excellent results and are very satisfied with the outcome. Conclusions. Our very early and limited experience indicates that high-power KTP/532 laser vaporization prostatectomy is feasible and appears to be safe and effective for quickly relieving bladder outlet obstruction due to BPH. Larger randomized clinical trials to compare this technique with standard transurethral resection of the prostate and more follow-up data are needed to determine its long-term efficacy and durability.

In vitro comparison of debonding force and intrapulpal temperature changes during ceramic orthodontic bracket removal using a carbon dioxide laser

The aim of this study was to develop a method to reduce the fracture of ceramic orthodontics brackets during debonding procedures. Lasers have been used to thermally soften the bonding resin, which reduces the tensile debonding force. Thermal effects of lasers may create adverse effects to the dental pulp. Previous studies have shown that no pulpal injury occurs when the maximum intrapulpal temperature rise stayed below 2 degrees C. This study investigated the effect of lasing time on intrapulpal temperature increase and tensile debonding force with a 18 watt carbon dioxide laser. Ceramic brackets were bonded to mandibular deciduous bovine teeth and human mandibular first premolars with a photoactivated bonding resin. Modified debonding pliers was used to accurately position the laser beam onto the ceramic bracket. Lasing time required to keep the maximum intrapulpal temperature rise below 2 degrees C was determined by the use of thermocouples inserted into the pulp chambers of the specimens. A tensile debonding force was applied on the control group without lasing and the experimental group was debonded after applying a predetermined lasing time with a carbon dioxide laser. It was found that there was a significance difference (P < 0.05) in tensile debonding force between the control group and the experimental group. It is feasible to use a laser for the debonding of ceramic brackets while keeping the intrapulpal temperature rise below the threshold of pulpal damage.

Enhanced beam characteristics of a discharge-pumped soft-x-ray amplifier by an axial magnetic field.

We report results of the study of soft-x-ray amplification in a discharge-created plasma under an externally applied axial magnetic field. This technique is observed to improve the uniformity and divergence of the beam of a 46.9-nm discharge-pumped Ne-like Ar soft-x-ray amplifier by decreasing the plasma density gradients at the time of lasing. At the optimum strength of 0.15 T, the magnetic field also causes an increase in the laser beam intensity. At higher fields the Zeeman effect is found to contribute to line broadening, decreasing the laser output. \textcopyright{} 1996 The American Physical Society.