In present-day single-rod/single-beam solar laser systems, the thermal lens effect is a serious issue that limits its ability for a scale-up to higher powers and improved beam quality. Aiming at resolving this shortcoming, the concept of a seven-rod/seven-beam solar pumping scheme is proposed. This scheme was composed of a first-stage heliostat-parabolic mirror system and a single large laser head. The large laser head consisted of seven fused silica compound parabolic concentrators, which transmitted and focused the concentrated solar radiation to each single-laser rod of small diameter, within a conical cavity, which enabled multiple passages of the pump rays. Consequently, each laser rod was pumped by only one-seventh of the total concentrated solar power, ensuring a significant reduction of the thermal induced effects in the laser rods. 13.3 W/m2 TEM00-mode solar laser collection efficiency was numerically achieved, representing an enhancement of 1.68 times over the experimental record from a single-rod prototype. 1.80 times improvement in solar-to-TEM00-mode laser power conversion efficiency was also registered in relation to the previous experimental record.
A multirod solar side-pumping concept is proposed to study the feasibility of multirod/multibeam laser systems in large-sized solar furnaces. This scheme was based on the one-megawatt solar furnace (MWSF) in Odeillo, France, which collected and concentrated solar rays into an input face of a solar homogenizer placed at the focal zone. At its output face, 12 laser heads were positioned, each of which was composed of a two-dimensional compound parabolic concentrator that focused the uniform solar radiation from the homogenizer’s output to an Nd:YAG rod mounted inside a fused silica flow tube. Each laser rod was pumped by one-twelfth of the total concentrated solar power transmitted through the homogenizer, ensuring a good thermal performance under highly concentrated solar power. A 22.84-kW total multimode solar laser power, corresponding to 12.48-W / m2 collection efficiency and 2.28% solar-to-laser power conversion efficiency, was numerically determined. The latter represents an enhancement of 1.75 times over the previous numerically calculated value for a multirod/multibeam laser scheme based on another one-MWSF near Tashkent, Uzbekistan.
We present here a tracking error compensation concept in solar-pumped lasers, by pumping two thin laser rods simultaneously, each rod by half of the solar collector area instead of the mostly used scheme with one thick rod pumped by a full solar collector area. A semicylindrical fused silica lens allows an efficient focusing of the concentrated solar power from the focal spot of the parabolic mirror into the two thin laser rods mounted within two compound parabolic concentrator-semicylindrical pump cavities. The multimode solar laser output power, the threshold pump power, and the slope efficiency of a single-rod scheme, a dual-rod scheme with two laser beams, and a dual-rod scheme with one laser beam are calculated both numerically and analytically, revealing a clear advantage of the dual-rod one laser beam scheme in terms of solar laser output power and threshold pump power. A large improvement in tracking error compensation capacity is numerically attained with this new approach, leading to 2.57 and 3.00 times enhancement in tracking error width at 10% laser power loss in ΔY (altitude) and ΔX (azimuth) errors, respectively, as compared to the most efficient end-side-pumped scheme by the same collection area.
A four-rod solar pumping concept is proposed for the significant improvement in TEM00-mode solar laser performance. A quadrangular pyramidal reflector is used to separate the focused solar rays from a 2.0-m diameter parabolic mirror into four focal spots. Four laser heads, each one consisting of a double-stage biconical lens/conical pump cavity and a small diameter Nd:YAG rod, are placed at each of the four focal zones. TEM00-mode laser output of 7.22 W is numerically obtained from each rod, resulting in 28.9 W (4 × 7.22 W) total TEM00-mode power from the four-rod scheme with 9.41 W / m2 collection efficiency. This value is 2.5 times more than that of the numerically calculated laser power collection efficiency from a single-rod pumped by the same parabolic mirror. A brightness conversion efficiency of 0.86% is achieved. Substantial improvements in TEM00-mode solar laser stability and thermal performance are also numerically demonstrated.
We demonstrated a solar-pumped laser with a heliostat–parabolic mirror system. A designed conical pump cavity with a water-filled quartz tube lens was used to couple efficiently the concentrated solar radiation from the focal zone of the primary concentrator into a 5.5-mm-diameter, 95-mm-length grooved Nd:YAG crystal rod within a gold-plated conical pump cavity. For 1.0-m2 effective solar radiation collection area, 20.1-W continuous-wave (CW) output laser power was obtained, corresponding to a total system slope efficiency of 5.04%. This value was 1.31 times higher than the previous with the same solar facility. For 1.5-m2 effective collection area, 34.6-W CW output laser power was achieved at the total system slope efficiency of 4.51%. A strong dependency of laser power on laser rod mounting position was also found.
We report here a compact pumping scheme for achieving large improvement in collection and conversion efficiency of a Nd:YAG solar-pumped laser by an innovative ring-array solar concentrator. An aspheric fused silica lens was used to further concentrate the solar radiation from the focal region of the 1.5-m-diameter ring-array concentrator to a 5.0-mm-diameter, 20-mm-length Nd:YAG single-crystal rod within a conical-shaped pump cavity, enabling multipass pumping to the laser rod. 67.3-W continuous-wave solar laser power was numerically calculated, corresponding to 38.2-W / m2 solar laser collection efficiency, being 1.22 and 1.27 times more than the state-of-the-art records by both heliostat-parabolic mirror and Fresnel lens solar laser systems, respectively. 4.0% conversion efficiency and 0.021-W brightness figure of merit were also numerically obtained, corresponding to 1.25 and 1.62 times enhancement over the previous records, respectively. The influence of tracking error on solar laser output power was also analyzed.
The conversion of sunlight into laser light by direct solar pumping is of ever-increasing importance because broadband, temporally constant, sunlight is converted into laser light, which can be a source of narrowband, collimated, rapidly pulsed, radiation with the possibility of obtaining extremely high brightness and intensity. Nonlinear processes, such as harmonic generation, might be used to obtain broad wavelength coverage, including the ultraviolet wavelengths, where the solar flux is very weak. The direct excitation of large lasers by sunlight offers the prospect of a drastic reduction in the cost of coherent optical radiation for high average power materials processing. This renewable laser has a large potential for many applications such as high-temperature materials processing, renewable magnesium-hydrogen energy cycle and so on. We propose here a scalable TEM00 mode solar laser pumping scheme, which is composed of four firststage 1.13 m diameter Fresnel lenses with its respective folding mirrors mounted on a two-axis automatic solar tracker. Concentrated solar power at the four focal spots of these Fresnel lenses are focused individually along a common 3.5 mm diameter, 70 mm length Nd:YAG rod via four pairs of second-stage fused-silica spherical lenses and third-stage 2D-CPCs (Compound Parabolic Concentrator), sitting just above the laser rod which is also double-pass pumped by four V-shaped pumping cavities. Distilled water cools both the rod and the concentrators. 15.4 W TEM00 solar laser power is numerically calculated, corresponding to 6.7 times enhancement in laser beam brightness.
To improve the efficiency of Nd3+-doped YAG solar laser, cross-pumped Cr3+ and Nd3+ co-doped YAG ceramic material has attracted more attentions in recent years. The sensitizer Cr3+ ions have broad absorption bands in the visible region. Despite the interests in Cr:Nd:YAG ceramic medium, researchers have achieved significant laser efficiencies with different Nd:YAG single-crystal rods. While it is clear about the effectiveness of Nd:YAG single-crystal rods for solar laser operation, there still exist some concerns about the advantages of Cr:Nd:YAG ceramics in solar-pumped lasers. A 0.9 m diameter Fresnel lens is used as an economical solar collector. A 4 mm diameter, 25 mm length 1.0 at% Nd:YAG single-crystal rod and a 0.1 at% Cr: 1.0 at% Nd:YAG ceramic rod are pumped alternatively within a conical cavity through a secondary concentrator. With the Nd:YAG rod, the maximum laser power is 12.3 W, corresponding to 19.3 W/m2 collection efficiency. With the Cr:Nd:YAG ceramic rod, the maximum laser power is 13.5 W, corresponding to 21.2 W/m2 collection efficiency. This result is, to the best of our knowledge, the highest collection efficiency achieved with Cr:Nd:YAG ceramic medium. There is also a 109% increase in slope efficiency. In summary, we have experimentally observed a moderate, but not significant, advantage of Cr:Nd:YAG ceramics over Nd:YAG single-crystal medium in both solar laser conversion and slope efficiency.
Solar-pumped solid-state lasers are promising for renewable extreme-temperature material processing and space power applications. An efficient Fresnel lens solar laser pumping approach is proposed here. The incoming solar power is firstly collected and concentrated by four 800 mm x 800 mm square Fresnel lenses and redirected by four plane mirrors to a central focal spot of 12 mm FWHM diameter, attaining 443 W concentrated solar power. Secondly for further concentration, both a set of four aspherical lenses and a fused silica sphere are positioned in the focal zone. Both side-pumping and end-pumping are achieved simultaneously for a 7 mm diameter by 12 mm length Nd:YAG single-crystal rod mounted within the sphere. Since there is no strong pump radiation absorption within the central core zone of the rod, thermal lensing effect is also minimized with the proposed scheme. A 600 mm length plane-plane resonant cavity is used to extract 1064 nm laser emission efficiently. Optimum pumping parameters and solar laser output powers are found through ZEMAX non-sequential ray-tracing and LASCAD laser cavity analysis. By taking into account 16 % of spectrum overlap between the 1.0 % Nd:YAG absorption spectrum and the solar spectrum, 183 W absorbed solar power is assumed in ZEMAX numerical analysis. Considering a round trip loss of 1.32 % for the resonant cavity, 45.2 W laser power is numerically attained through LASCAD software, corresponding to 17.7 W/m2 collection efficiency. The proposed pumping scheme presents an excellent compromise between the laser output power and its beam quality.
To obtain a good compromise between collection efficiency and brightness figure of merit of solar-pumped lasers, a new side-pumping scheme is proposed. Firstly the solar radiations are collected and concentrated by six 700 mm diameter Fresnel lenses. The concentrated solar radiations are subsequently reflected by six plane folding mirrors with 95% reflectivity, into a common focal spot. This allows the concentration of 1740 W solar power with about 6.4 W/mm2 peak solar flux. A secondary concentrator is composed of six aspheric fused silica lenses, positioned around a 40 mm radius fused silica sphere, compressing all the concentrated solar radiation from the six Fresnel lenses into an 8 mm diameter by 9 mm length Nd:YAG single-crystal rod. By positioning the spherical concentrator slightly above the aspherical lenses, a more uniform absorption profile is achieved. Mechanical support with a water cooling system ensures an efficient cooling to the laser medium. Optimal laser parameters are found through ZEMAX™ and LASCAD™ numerical analysis software. Only 16% of the solar power is absorbed by Nd:YAG medium. Solar laser power of 42.6 W is numerically calculated, reaching a collection efficiency of 18.5 W/m2. For a 400 mm plane-concave resonance cavity with –5m radius of curvature, M2x = M2y = 22 beam quality factors are numerically predicted. A near uniform pump absorption profile can be achieved by increasing the number of Fresnel lens and folding mirrors.
A novel solar laser uniformly pumped by six Fresnel lenses is proposed here. The incident solar radiation is firstly collected and concentrated by six 0.8 m diameter Fresnel lenses and then reflected by other six plane mirrors to a central focal zone, where a laser head is mounted. About 2.5 kW solar power with 3.5 W/mm2 peak solar flux can be achieved in the focal zone. The laser head is composed of a fused silica six-sphere type secondary concentrator that further compresses the concentrated solar power from the six Fresnel lenses-plane mirrors to a core-doped YAG Nd3+:YAG ceramic disk. Optimum pumping parameters and solar laser output powers are found through ZEMAX non-sequential ray-tracing and LASCAD laser cavity analysis, respectively. The laser resonant cavity is formed by a PR 1064 nm output coupler and a HR 1064 nm plane reflector. An 8 mm diameter central hole is drilled through the six-sphere type concentrator to allow the extraction of laser power from the disk. Since only 16 % of the useful solar power is absorbed by the Nd:YAG medium, for 950 W/m2 of terrestrial solar irradiation, the effective solar pump power of 456 W is assumed in ray-tracing analysis. 72.2 W of multimode laser power is predicted for an 8 mm diameter gain medium embedded within a conical undoped YAG cladding, reaching the collection efficiency of 24.1 W/m2. M2 = 16.6 is numerically calculated, corresponding to the brightness figure of merit of 0.26 W. A near uniform absorbed pump profile is achieved.
Incoming solar energy is firstly collected 137 small parabolic mirrors, 180mm in diameter, 210mm in focal length and
then coupled by 137 optical fibers with 2mm in diameter each, to a diffusion bounded thin-disk Nd:YAG laser material.
The flexibility of optical fiber allows the placement of laser cavity in a convenient place away from the solar collection
mirrors. The conical polishing of the fiber output sections permits further enhancement of pump light absorption by the
Nd:YAG thin-disk, diffusion bounded to an undoped YAG cap with 80mm maximum diameter. For optimal pumping
condition with 1.8mm diameter polished tip, 20W laser power was numerically calculated, corresponding to a collection
efficiency of 5.9 W/m2. M2 factors of Mx2=88.5 and My2=89.4 were also attained, indicating an almost symmetrical
absorption profile. The proposed scheme can provide a solution to the thermal problems that has plagued the solarpumped
lasers for many years.
Since the first reported Nd:YAG solar laser, researchers have been exploiting parabolic mirrors and heliostats for
enhancing laser output performance. We are now investigating the production of an efficient solar-pumped laser for the
reduction of magnesium from magnesium oxide, which could be an alternative solution to fossil fuel. Therefore both
high conversion efficiency and excellent beam quality are imperative. By using a single fused silica light guide of
rectangular cross section, highly concentrated solar radiation at the focal spot of a stationary parabolic mirror is
efficiently transferred to a water-flooded V-groove pump cavity. It allows for the double-pass absorption of pump light
along a 4mm diameter, 30mm length, 1.1at% Nd:YAG rod. Optimum pumping parameters and solar laser output power
are found through ZEMAXTM non-sequential ray-tracing and LASCADTM laser cavity analysis. 11.0 W of multimode
laser output power with excellent beam profile is numerically calculated, corresponding to 6.1W/m2 collection efficiency.
To validate the proposed pumping scheme, an experimental setup of the double-stage light-guide/V-groove cavity was
built. 78% of highly concentrated solar radiation was efficiently transmitted by the fused silica light guide. The proposed
pumping scheme can be an effective solution for enhancing solar laser performances when compared to other side-pump
Aiming at studying solar photocoagulation in biological tissue with both low energy and high energy portions of solar
spectrum, a simple color separation technique is proposed. The chromatic aberration characteristic of Fresnel lens is
exploited to achieve color separation by a plane mirror with a large central elliptical hole, reflecting the solar radiation
above 600nm to one fused silica light guide, while allowing the passage of the remaining radiation to another guide.
ZEMAX™ ray-tracing code is used to optimize the performance of each optical component. To attain a stable solar
coagulation, the prototype is tested on a two-axis solar tracker. The ex vivo measurement is performed on chicken
breasts at the solar power level of 30W and the exposure time of 60 seconds, attaining a uniform coagulation over a large
area of 15mm x 15mm. A strong dependence of the penetration depth on wavelength is observed. Our cost effective solar
photocoagulation prototype produces the same type and extent of tissue coagulation ordinarily achieved with surgical
The use of LED devices for phototherapy has been expanding in the last decade. This technology provides a safer
emission spectrum in large target tissue areas when compared to laser emissions. For enhancing the phototherapeutic
effects of red light emitted by LEDs, a simple optical concentrator capable of efficient light concentration and
homogenization was developed. The LEDs wavelength of 660 nm is coincident with an absorption peak of the
mitochondrial photoreceptor molecule cytochrome c oxidase. The prototype was optimized by non-sequential ray-tracing
software ZEMAX, attaining both excellent light uniformity and 50mW/cm2 irradiance at the concentrator output end.
Heat emanated from the LEDs source is effectively dissipated by the side walls of the concentrator, ensuring a nearly
constant temperature environment for tissue treatment. The prototype was tested on cutaneous hyperpigmented marks
caused by cupping in two healthy volunteers. Marks were irradiated by LEDs radiations with or without the use of
concentrator respectively. Equal exposure durations and light fluences were tested. The use of the concentrator-coupled
LEDs source revealed an activation of blood movement immediately after LEDs exposure, an effect not attainable by the
LEDs source without the concentrator even at extended exposure time. Promising futures for the treatment of
inflammation, tissue repair and skin rejuvenation could be expected by adopting this simple technique.
By using a solid-core fused silica light guide of a large numerical aperture, high power solar energy can be transmitted economically to a convenient place outside the focal area of a primary parabolic concentrator. The light flux distribution at the focal phase was firstly measured and the intercept factors of angle dependence were calculated individually for the light guides of 2, 4, 5.8, 7.3, 10, 12 and 14 mm diameters. By taking into account the influence of the loss dependence ηg(Φi) on incident angled, a simple model for the efficiency calculation of the whole system was introduced. The light guides were placed separately at the focus of the primary concentrator and the output powers of 50, 206, 374, 506, 690, 770 and 818W were successfully measured, attaining the transmission efficiency of 65 percent for the light guided of 14mm diameter. In length dependence loss measurement, the attention of -1.87 dB/m was found. The transmission property of a curved light guide was also tested, showing no significant loss in output power. The utilization of high power solar energy inside rooms or other thermally insulated places can therefore be expected. A novel light guide with an angular transformed input end was also put forward at the end. The input rays of large angles were transformed into the output rays of small angles by the angular transformed polished direction on a light guide. Both high transmission efficiency and high output power were achieved.
Flexible optical fibers and fiber bundles can be used to transfer concentrated sunlight to a desirable place where it could be used to pump a solid state laser. One flexible fiber bundle was built. It consisted of seven optical fibers. The output section of optical fibers were polished to an hexagonal form. The bundle was placed at the focus of a primary parabolic mirror to capture the solar energy in the core-region of the focal spot. The radiation exiting the fibers was concentrated with a DCPC or with a long conical concentrator. An optical adhesive was utilized to bond the fiber bundle and the concentrator together. For non-contact type concentration, a DCPC was utilized and no index compensating liquid was necessary. A moderate optical flux of 13 W/mm2 was measured, with a large angular divergence as expected together with a non-homogeneous light distribution from the output end of the DCPC concentrator; both were certainly responsible for the unsuccessful attempts at pumping the laser. Hence a long conical concentrator was designed and built. Experimental results shown that both the incident ray acceptance capability and the output light quality are better than the DCPC. A solar flux of about 20 W/mm2 was obtained. Success at pumping the crystal laser can now be expected and will be reported elsewhere.
The notion of transporting concentrated solar energy radiation by flexible optical fibers or fiber bundles has been developed for a variety of uses. With the aim of CW pumping a laser crystal outside the focusing area of a primary parabolic mirror, an optical fiber bundle with a frustum-type output end was used to transmit and concentrate solar energy to a flux level high enough to pump a solid state laser. The transmission properties of a fiber optic frustum-type concentrator was first analyzed with the help of a ray-tracing program, which revealed strong influences of both output diameter and length on the transmission efficiency of a frustum concentrator. The idea of achieving an ideal angular transformer with fiber optic technology in the area of nonimaging optics was also proposed. The output section of each optical fiber was polished to form a hexagonal frustum. When seven of these polished frusta from the optical fibers were joined together, a novel solar energy concentrator was obtained. The output power from the concentrator end was 67 W, corresponding to the solar flux of 23 W/mm2. The experimental results of transporting and concentrating the solar radiation by using four fiber bundle with a square frustum output end was also reported. The maximum solar flux of 28 W/mm2 was obtained with a single optical fiber of conical output end.
Flexible optical fibers and fiber bundles can be used to transfer solar energy to a desirable place, where it could be used either to pump a laser crystal or to carry out other useful mechanical, chemical or thermal processings. Two flexible fiber-optic bundles were built. Each bundle consists of 19 optical fibers of 1.5 mm diameter each. The input section of each single fiber is polished to form a hexagonal column. When the input columns were joined together, two compact fiber-optic bundles were formed, leaving no dead space between the fibers and hence, the concentrated solar energy was transmitted without extra loss. Two off-axis parabolic mirrors with hexagonal form were held onto a solar tracker which continuously tracks the Sun. With an incident intensity of 650 W/cm2, each primary mirror captured 143 W solar energy and concentrated it into a light spot of hexagonal form, which matches well with the input area of the fiber-optic bundle. Solar energy of 100 W was successfully delivered by each bundle, with transmission efficiency of 70%. The two fiber bundles were also combined to form a large bundle for 200 W solar energy delivery.
The solid core polycrystalline middle infrared region (MIR) optical fiber has no bending loss and has been successfully used as a flexible CO2 laser guide for medical operations. By using a suitable cooling we have improved the power handling capacity for (phi) 1 mm MIR- fiber to 50 W. However this is far less than the needs for most nonmedical applications, like the 500 W requirements for cork cutting. For this purpose a method was developed to join together several fibers and transmit more power. With a fiber bundle composed of 4 MIR fibers, about 120 W is transmitted (with about 50% efficiency for cw power). Preliminary tests were made to improve the power handling capacity and efficiency, so that, in future, about 500 W CO2 laser power can be delivered by using a larger fiber bundle.
Four multimode fiber optic sensing units are combined to form a simple fiber optic silicon impact sensor. Three high resonant frequency sensing units are used to localize the impact point by detecting the impact induced acoustic waves and their relative arrival times. The impact location accuracy of 4 cm is achieved over a 1 m X 2 m area. The averaged signal output from four sensing units is utilized to compensate the acoustic attenuation effect of the real impact magnitude. The novel linear design of each sensing unit structure offers an excellent linearity for impact magnitude detection.
The autofluorescence of cancerous and normal human stomach tissues was measured in vitro, by fluorescence spectroscopy, within three hours of surgery ablation. A new fluorescence emission band, centered at about 380 nm for the cancerous stomach tissue is reported, for 340 nm excitation. This band is practically absent for the normal tissue when this is excited at the same wavelength. For UVB excitation (between 283 and 305 nm) the emission bands are centered around 350 nm and 470 nm, for both tissues, in agreement with the literature. The ratios of the fluorescence intensities for cancerous and normal tissues are measured at the center of the three bands, the intensity for the diseased tissue being always higher than for the normal one. The presence of a new band centered at 380 nm, combined with the intensity ratios, may prove of great relevance towards early in vivo detection of stomach cancer.
Silicon micromechanics technology has formed the basis of a range of compact and reliable sensors, measuring variables such as pressure, force and acceleration. Most micromechanical sensors require some form of electrical read-out. Therefore, these sensors are classified as electrically active. Electrically passive sensors also have many applications, and the best examples of such sensors are those based on fiber optic technology. In this paper, we describe a sensor which combines the advantages of both silicon micromechanics and fiber optics. Specifically, an accelerometer has been fabricated, and initial results on the performance of this device are presented.
In multiphoton ionization mass spectrometry, the increase in laser pulse intensity leads to an additional absorption of photons by molecules, and the degree of fragmentation also increases significantly. A laser pulse is usually focused to interact with the molecular beam only once, and the laser power is then wasted. A novel device for increasing the laser pulse intensity in a multiphoton ionization mass spectrometer is put forward. By collecting and refocusing the laser pulse precisely onto the laser-molecules interaction region, the laser pulse intensity in this region is increased. By using two UV reflectors and a lens, the 0.3 ns delayed laser pulse is guided back to superimpose almost simultaneously onto the original pulse. UV optical fiber is used to guide the residual laser pulse out from the vacuum chamber. The accurate interaction between light pulses and molecules is obtained by monitoring this output laser pulse intensity. By using this device, the mass spectrum of benzene was produced, which showed a stronger fragmentation than was obtained with the usual method at the same laser power. This laser intensity enhancement device is of practical importance to applications where a strong local laser field is needed.
A novel three-dimensional interferometric and fiber-optic displacement measuring probe is described. As an important sensing part of a coordinate measuring machine, this compact measuring probe is successfully used in coordinate and surface scanning measurements of several types of complicated workpieces in precision engineering metrology. It is also applicable to three-dimensional vibration measurement. The distinguishing feature of this probe resides in its higher measurement accuracy on a relatively large measuring range, as compared with other conventional electric 3-D measuring probes commonly used in coordinate measuring machines. +/- 0.2 micrometers accuracy is achieved in a +/- 100 micrometers range in any spatial direction. The measuring force is less than 0.33N. This probe is very suitable for continuous surface scanning measurement. This three-dimensional interferometric and fiber-optic measuring probe consists mainly of three parts. The resilient mechanical part provides a universal movement for the measuring tip. The interferometric and fiber-optic small displacement sensing part measures this universal movement in the X, Y, and Z directions simultaneously and precisely. The opto-electronic signal detecting and processing part gives a real-time digital display of the measuring tip spatial displacement.