Conventional Solid-state Lasers Research Articles

Burn depth assessment by dual-wavelength light emitting diodes-excited photoacoustic imaging in rats.

Accurate burn depth assessment is crucial to determine treatment plans for burn patients. We have previously proposed a method for performing burn depth assessments based on photoacoustic (PA) imaging, and we have demonstrated the validity of this method, which allows the successful detection of PA signals originating from the blood under the bloodless burned tissue, using rat burn models. Based on these findings, we started a clinical study in which we faced two technical issues: (1) When the burn depth was shallow, PA signals due to skin contamination and/or melanin in the epidermis (surface signals) could not be distinguished from PA signals originating from the blood in the dermis; (2) the size of the system was too large. To solve these issues, we propose a burn depth diagnosis based on dual-wavelength light emitting diodes (LEDs)-excited PA imaging. The use of LEDs rendered the system compact compared to the previous one that used a conventional solid-state laser. We replicated human burned skin by applying a titrated synthetic melanin solution onto the wound surface in albino rat burn models and measured their burn depths by PA excitation at 690 and 850 nm, where melanin and haemoglobin show greatly different absorption coefficients. As a result, the surface signals were eliminated by subtracting the PA signals at 690 nm from those at 850 nm. The resultant estimated burn depths were strongly correlated with the histological assessment results. The validity of the proposed method was also examined using a burn model of rats with real melanin.

Optical Coherence Tomography Following Panretinal Photocoagulation Demonstrating Choroidal Detachment

Retinal laser therapy such as panretinal photocoagulation can be associated with complications, including rare cases of choroidal detachment. This report describes high-resolution optical coherence tomography (OCT) imaging after retinal laser panretinal photocoagulation (PRP) in patients with proliferative diabetic retinopathy (PDR) demonstrating choroidal detachment. A series of three sequential patients with high-risk proliferative diabetic retinopathy who were PRP laser naïve were examined with spectral-domain OCT immediately after green solid-state laser or PASCAL® PRP treatment. All three patients demonstrated a significant choroidal detachment immediately after PRP treatment. By one month after PRP, the choroidal detachment resolved spontaneously in all patients. OCT examinations were performed to detect and evaluate the severity and the change of choroidal detachment and thickness measurements were quantified and demonstrated a mean decrease in choroidal thickness of 122 µm (p < 0.05 in all patients). Conventional green solid-state laser and PASCAL® laser both have the risk of developing complications such as choroidal detachment. While the rate of choroidal detachment has been reported to be quite low, this could be due to subclinical, self-limited, choroidal detachments. The risk could be larger than previously reported using modern high-resolution clinical optical imaging such as OCT.

Ion-Doped Photonic Crystal Fiber Lasers

Compared with conventional solid-state lasers, fiber lasers have the advantages of small size, simple cooling system, and good output beam quality, enabling them an extended service lifetime in industrialized environments. Periodically arranged photonic crystals have been the most important gain medium for high-power laser applications, which overcame the problems in fiber lasers such as small mode field, low degree of nonlinearity, and non-adjustable dispersion. In this mini-review, we summarize the recent advances of typical ion-doped photonic crystal fiber lasers doped, discuss the challenges, and provide an outlook on the future developments in ion-doped photonic crystal fiber lasers.

A High Power, Frequency Tunable Colloidal Quantum Dot (CdSe/ZnS) Laser.

Tunable lasers are essential for medical, engineering and basic science research studies. Most conventional solid-state lasers are capable of producing a few million laser shots, but limited to specific wavelengths, which are bulky and very expensive. Dye lasers are continuously tunable, but exhibit very poor chemical stability. As new tunable, efficient lasers are always in demand, one such laser is designed with various sized CdSe/ZnS quantum dots. They were used as a colloid in tetrahydrofuran to produce a fluorescent broadband emission from 520 nm to 630 nm. The second (532 nm) and/or third harmonic (355 nm) of the Nd:YAG laser (10 ns, 10 Hz) were used together as the pump source. In this study, different sized quantum dots were independently optically pumped to produce amplified spontaneous emission (ASE) with 4 nm to 7 nm of full width at half-maximum (FWHM), when the pump power and focusing were carefully optimized. The beam was directional with a 7 mrad divergence. Subsequently, these quantum dots were combined together, and the solution was placed in a resonator cavity to obtain a laser with a spectral width of 1 nm and tunable from 510 to 630 nm, with a conversion efficiency of about 0.1%.

Vortex and LG01-mode Nd:YAG laser involving a circular Dammann grating

By introducing a circular Dammann grating (CDG) into the pump unit, we demonstrated an end-pumped Nd:YAG laser that emitted a vortex and first-order LG mode with high laser efficiency and high power. In our scheme, the CDG was used to reshape the pumping light into an annular profile, and the adaptation of it was realized easily by inserting it into the pump unit of a conventional end-pumped solid-state laser; the laser cavity was simple, compact, and consisted of only a laser crystal and an output coupler. The beam power of this laser reached 1.86 W at an absorbed pump power of 6.38 W with a slope efficiency of 34.5%.

Extending laser plasma accelerators into the mid-IR spectral domain with a next-generation ultra-fast CO2 laser

Expanding the scope of relativistic plasma research to wavelengths longer than the λ/≈ 0.8–1.1 μm range covered by conventional mode-locked solid-state lasers would offer attractive opportunities due to the quadratic scaling of the ponderomotive electron energy and critical plasma density with λ. Answering this quest, a next-generation mid-IR laser project is being advanced at the BNL ATF as a part of the user facility upgrade. We discuss the technical approach to this conceptually new 100 TW, 100 fs, λ = 9–11 μm CO2 laser BESTIA (Brookhaven Experimental Supra-Terawatt Infrared at ATF) that encompasses several innovations applied for the first time to molecular gas lasers.BESTIA will enable new regimes of laser plasma accelerators. One example is shock-wave ion acceleration (SWA) from gas jets. We review ongoing efforts to achieve stable, monoenergetic proton acceleration by dynamically shaping the plasma density profile from a hydrogen gas target with laser-produced blast waves. At its full power, 100 TW BESTIA promises to achieve proton beams at an energy exceeding 200 MeV.In addition to ion acceleration in over-critical plasma, the ultra-intense mid-IR BESTIA will open up new opportunities in driving wakefields in tenuous plasmas, expanding the landscape of laser wakefield accelerator (LWFA) studies into the unexplored long-wavelength spectral domain. Simple wavelength scaling suggests that a 100 TW CO2 laser beam will be capable of efficiently generating plasma ‘bubbles’ a thousand times greater in volume compared with a near-IR solid state laser of an equivalent power. Combined with a femtosecond electron linac available at the ATF, this wavelength scaling will facilitate the study of external seeding and staging of LWFAs.

Theoretical study of relaxation oscillations in a free-running diode-pumped rubidium vapor laser

Diode-pumped alkali lasers (DPALs) have undergone rapid development to become one of the most promising candidates for use as high-power laser sources in recent years. Relaxation oscillation (RO) is a common phenomenon related to the dynamic process in the time domain. Sometimes, it is applied in parameter measurement, but sometimes it should be eliminated to ensure stable output. In this paper, we develop a kinetic model to study the RO features of a DPAL, which are different from those of a conventional solid-state laser. The results reveal that the cell temperature, buffer gas pressure, pumping power, cavity length, and reflectance of an output coupler affect the characteristics of ROs. Among these parameters, the cell temperature and the pumping power exert relatively strong influences on the waiting time of the first spike in the RO. Additionally, the cavity length cannot markedly affect the peak value of the laser intensity. These new analyses should prove useful for understanding the dynamic process of DPAL oscillation and for the future design of a steady high-powered DPAL.

A perspective on novel sources of ultrashort electron and X-ray pulses

Recently, much attention has been devoted to the development of new pulsed sources of radiation for investigating matter with atomic scale temporal and spatial resolution. While much has been achieved thanks to modern ultrafast laser technology, the ultimate coherent light source, the X-ray free electron laser (X-FEL), promises to deliver the highest X-ray photon flux in the shortest pulses at energies unreachable by conventional solid-state lasers. In parallel, other approaches that utilize electrons in table-top setups as a probe have been developed demonstrating the potential for a valid complement to X-ray based techniques. Here, we consider yet another possible avenue in which the technology of electron diffraction and imaging is pushed further; we estimate the interest and performances of a femtosecond high energy electron microscope and propose a hybrid experiment with relativistic electrons as a probe and fs X-ray pulses as a pump taking advantage of both technologies.

Theoretical study of the lock-in in pulsed laser gyroscopes

The problem of lock-in in a pulsed laser gyroscope, which may be a new kind of rotation sensor, is studied theoretically. Using a new method, we derive a generalized expression for the lock-in rotation rate, which can be applied to both conventional continuous wave and solid-state pulsed laser gyroscopes. A Gaussian pulse, secant hyperbolic pulse, and super-Gaussian pulse are taken as examples for numerical calculation of the pulsed laser gyroscope lock-in rotation rate; the results indicate that a super-Gaussian pulse is more suitable than the other two. For a super-Gaussian pulsed laser gyroscope, the dead band disappears when the distance between the scatter element and the crossover point exceeds the full width at half maximum (FWHM) of the pulse, whereas for the secant hyperbolic pulse type the distance must be about 4.5 times greater than the FWHM.

The Analytical Solution of Rate Equations in End-Pumped Fiber Lasers with Minimum Approximation and Temperature Distribution during the Laser Operation

High-power fiber lasers have many applications in medicine, military, industry, etc. due to their advantages. They have high beam quality and high efficiency with respect to the conventional solid-state lasers [1–8]. In high-power regime, thermal effects influence the laser operation and cannot be neglected [9]. The thermal effects will produce the poor beam quality and knowledge of them will be important in laser design. In this paper, as the first, we analytically solved the rate equations in single end-pumped Yb-doped fiber laser. To solve the rate equations, we considered the minimum approximation, this means taking into account the upper population density of fiber and absorption cross-section, which have been ignored in the literature [10]. So, we improved the analytical rate equation solutions and found the output laser power versus input parameters. By using the output power of the laser, we solved the heat conduction equation in the laser during operation. In this way, we considered heat deposited in the fiber due to pump and laser powers and solved the heat equation. The temperature distribution during the operation has been obtained and compared with temperature distribution in turn-off. The results were applied for Yb-doped fiber lasers and the plots have been discussed.

Fiber lasers: A future space technology [same article as "Fiber lasers: A future technology for lasers in space", ibid, vol. 23, n. 4, pp. 25-30, 08

The constraints of operation in space have largely precluded the use of conventional solid-state systems for applications including remote sensing, communication relays, and active radars. A new technology, lasers, may offer all of the needed features at an affordable price. An appealing aspect of the is that it does not need a rigid optical bench. Only the output end of the need be held in rigid reference to the optical tracking system. Design, fabrication, and testing of the resonator is generally the most expensive and longest lead part of the effort for conventional solid-state lasers. Advances in Fiber Optic technology and devices mean that the fiber laser need not be a simple device but may be a complex system employing sophisticated technology such as wavelength selective Bragg reflectors and nonlinear optical frequency shifters. Three companies have recently obtained single-mode outputs of 3540 watts single mode at 1.03-1.1 microns.

Fiber lasers: A future technology for lasers in space

The constraints of operation in space have largely precluded the use of conventional solid-state laser systems for applications including remote sensing, communication relays, and active laser radars. A new technology, fiber lasers, may offer all of the needed features at an affordable price. An appealing aspect of the fiber laser is that it does not need a rigid optical bench. Only the output end of the fiber need be held in rigid reference to the optical tracking system. Design, fabrication, and testing of the laser resonator is generally the most expensive and longest lead part of the effort for conventional solid-state lasers. Advances in fiber optic technology and devices mean that the "fiber laser" need not be a simple device but may be a complex system employing sophisticated technology, such as wavelength selective Bragg reflectors and nonlinear optical frequency shifters. Three companies have obtained single-mode outputs of 35 - 40 watts single mode at 1.03 - 1.1 mu.

Miniaturization and Power Scaling of Fundamental Mode Optically Pumped Semiconductor Lasers

We demonstrate that TEM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">00</sub> mode optically pumped semiconductor lasers (OPSLs) may be scaled to tens of watts in the visible wavelength range using laser cavities an order of magnitude smaller than those of conventional solid-state lasers. In particular, we show that the output power may be scaled linearly by increasing the number of optically pumped semiconductor (OPS) devices and derive a unique solution for a dynamically stable resonator that is independent of the physical cavity length and internal design. This enables miniaturization of high-power OPS lasers to ~1 cm footprints without compromising many resonator performance metrics. The results are applied to demonstrate a 15-mm footprint cavity producing 7.3-W output at 486 nm, and a cavity with two OPS chips with 24-W output at 561 nm. In addition, we show that efficient TEM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">00</sub> mode performance may be realized using free-space-coupled, high-power laser diode bars. Single-frequency operation is also demonstrated, and an rms noise level less than 0.01% is achieved.

High‐power vertical external‐cavity surface‐emitting lasers

Recently multiwatt power levels have been generated from Vertical External-Cavity Surface-Emitting Lasers in high quality spatially symmetric output beams. While these results are very impressive for a high brightness semiconductor source, they have largely been achieved in a wavelength band already well served by conventional solid-state lasers. To fully realise the potential of this technology, the wavelength versatility offered by the semiconductor materials must be utilized. Significant power scaling at wavelengths away from 1µm is a key technical challenge for the VECSEL developer. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Applications of High Power Single-Mode Fiber Lasers to Novel Microwelding and Micromachning

Single-mode fiber lasers have many advantages over conventional solid-state lasers, which include high beam quality, no need for cooling, high conversion efficiency, compactness, long life time and so on, attracting attention as an industrial tool for materials processing due to rapid increase in the output power. Present article overviews recent status of the applications of high-power single-mode fiber laser to laser materials processing including microwelding and micromachining.

Free-Space and Intermolecular Interaction Effects on the Local-Chain Rotational Relaxation Dynamics in Dye + Polymer Lasing Materials

Dielectric relaxation spectroscopy (DRS) and thermally stimulated depolarization currents (TSDC) are combined to analyze the secondary (β) side-chain relaxation mode of poly(methyl methacrylate) (PMMA) in conventional solid-state laser matrices. The response of undoped PMMA is compared with that of mixtures with fluorescent dyes: the highly polar and ionic rhodamine 6G/Cl- and pyrromethene 567 dyes and the neutral and apolar substituted perylene and perylimides. Variations in characteristic features of the β relaxation, such as the spectral position and the relative strength of the thermocurrent and dielectric loss bands as well as the absolute values and the width of the distribution in apparent activation energies (Ea), are exploited to isolate different types of intermolecular and intramolecular guest−host interactions. The results are interpreted in view of opposing effects on the relaxation characteristics of the pendant groups. In the presence of the perylene/perylimide dyes the β process is mainly influenced by variations in the local free space: by increasing the size of the dye molecule, the (re)orientation of the ester carbonyl side groups is more effectively hindered (i.e., increased Ea and antiplasticization). In contrast, in the xanthene/pyrromethene + PMMA mixtures, dipole−dipole and electrostatic interactions and charge-transfer reactions may be considered to control the dynamics of the β relaxation mode. The complementary character of the two dielectric techniques and possible relationships between the dielectric results and optical characteristics of each blend are discussed.

Fluorescence lifetime system for microscopy and multiwell plate imaging with a blue picosecond diode laser

We report a wide-field fluorescence lifetime imaging (FLIM) system that uses a blue picosecond pulsed diode laser as the excitation source. This represents a significant miniaturization and simplification compared with other time-domain FLIM instruments that should accelerate the development of clinical and real-world applications of FLIM. We have demonstrated this instrument in two configurations: a macroimaging setup applied to multiwell plate assays of chemically and biologically interesting fluorophores and a microscope system that has been applied to imaging of tissue sections. The importance of the adjustable repetition rate of this laser source is discussed with respect to noise reduction and precision in the lifetime determination, illustrating a further significant advantage over conventional mode-locked solid-state lasers.

Tunable, femtosecond pulse source operating in the range 106–133 m based on an Yb^3+-doped holey fiber amplifier

Summary form only given. Wavelength tunable femtosecond optical pulse sources have applications in areas as diverse as ultrafast spectroscopy, materials processing, optoelectronics, nonlinear optics and optical chemistry. In the past, such sources have been available only in limited wavelength ranges and were realized using solid state lasers with complex, high precision cavities. More recently, the soliton self frequency shift (SSFS) in silica fibers has been exploited to obtain tunable femtosecond pulses; tuning from 1.55-2.2 /spl mu/m was previously reported in conventional silica fiber, and tuning from 1.3-1.6 /spl mu/m has been demonstrated using tapered microstructured fiber. Here we report what we believe is the first demonstration of a continuously tunable soliton source in the wavelength range 1.06-1.33 /spl mu/m, a wavelength range that is difficult to access using conventional solid state laser technology. The system is based on diode pumped Yb/sup 3+/ doped silica fiber components, and operates at mW average input power levels in a 4.7 m length of fiber.

Mode-scalable fiber-based chirped pulse amplification systems

A new generation of compact and robust ultrashort pulse lasers is currently emerging based on rare-earth doped fiber gain media. This paper reviews the development of high-power fiber technology, which recently has led to millijoule energies and /spl sim/10 W average powers from various femtosecond fiber systems. These results indicate that fiber technology has a significant potential to replace conventional solid-state lasers and promises important advantages both for practical use and for achieving high powers and energies. Chirped pulse amplification and different mode-size scaling techniques compose the foundation of this ultrashort-pulse fiber technology. Mode-size scaling can be achieved either by using multimode core fibers, which can produce a diffraction-limited beam at the fiber amplifier output, or by "mode-cleaning" of multimode core fiber output through saturated optical parametric amplification.

Spectral Output and Spiking Behavior of Solid-State Lasers

Experiments show that conventional solid-state lasers can go into oscillation simultaneously in many modes. This is somewhat surprising since it appears impossible to ``eat holes'' in temperature-broadened lines and thus only one or, at most, a few modes should be able to oscillate. However, the spatial variation in the field intensity of the various modes produces nonuniform distributions in the inverted population and one can show that there is little tendency for these distributions to smooth out due to spatial cross relaxation. Such nonuniform distributions could lead to simultaneous oscillation in many modes. Formulas which relate the number of unstable modes to the pump power and various other maser parameters are obtained. The results show that it is exceedingly difficult to obtain single mode operation in conventional masers at high pumping levels. Ways to avoid a nonuniform distribution density and methods to achieve high-power single-mode operation in practice are discussed. It is also possible to show the effect of slow spatial cross relaxation on the spiking behavior.