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ABSTRACT: A new type of diffractive optical element for detecting and measuring the power distribution of transverse modes emanating from radially symmetric laser resonators is presented. It is based on a relatively simple straightforward design of a phase-only diffractive optical element that serves as a matched filter, which correlates between specific prerecorded transverse modes with a certain azimuthal mode order and those in the incident laser light. Computer simulations supported by experimental results demonstrate how such elements can accurately detect modes with spiral phases and provide quantitative results on the modal power distribution.
Applied Optics 12/2007; 46(32):7823-8. · 1.41 Impact Factor
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ABSTRACT: A method for increasing the output energy from newly developed passively Q-switched Er:glass eyesafe lasers is presented. The increase of energy is achieved by incorporating binary phase elements inside the laser cavities. Experimental results reveal that the output energies can be increased by more than a factor of two. Moreover, by manipulating the output phase with the binary phase elements, the peak energy density in the far field is increased by more than a factor of 4.5.
Applied Optics 11/2007; 46(30):7426-31. · 1.41 Impact Factor
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ABSTRACT: Multimode laser operation is usually characterized by high output power, yet its beam quality is inferior to that of a laser with single TEM00 mode operation. Here we present an efficient approach for improving the beam quality of multimode laser resonators. The approach is based on splitting the intra-cavity multimode beam into an array of smaller beams, each with a high quality beam distribution, which are coherently added within the resonator. The coupling between the beams in the array and their coherent addition is achieved with planar interferometric beam combiners. Experimental verification, where the intra-cavity multimode beam in a pulsed Nd:YAG laser resonator is split into four Gaussian beams that are then coherently added, provides a total increase in brightness of one order of magnitude. Additional spectral measurements indicate that scaling to larger coherent arrays is possible.
Optics Express 05/2005; 13(7):2722-30. · 3.59 Impact Factor
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ABSTRACT: We report on efficient coherent addition of spatially incoherent multimode laser beam distributions. Such addition is demonstrated within a multi-channel laser resonator configuration, obtaining more than 90% combining efficiency while preserving the good beam quality. We explain the rather surprising physical phenomenon of coherently adding spatially incoherent light by self-phase-locking of each of the modal components within the multimode beams. Our approach could lead to significantly higher output powers concomitantly with good beam qualities than were hitherto possible in laser systems.
Optics Express 11/2004; 12(20):4929-34. · 3.59 Impact Factor
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ABSTRACT: We present an approach for efficient conversion of a single-high-order-mode distribution from a laser to a nearly Gaussian distribution and vice versa. It is based on dividing the high-order mode distribution into equal parts that are then combined together coherently. We implement our approach with several optical arrangements that include a combination of discrete elements and some with single interferometric elements. These arrangements are analyzed and experimentally evaluated for converting the TEM01 mode distribution with Mx(2) = 3 to a nearly Gaussian beam with Mx(2) = 1.045 or Mx(2) = 1.15. The basic principle, design, and experimental results obtained with several conversion arrangements are presented. The results reveal that conversion efficiency is typically greater than 90%, compared with theoretical ones. In addition, some arrangement is exploited for converting the fundamental Gaussian-beam distribution into the TEM01 mode distribution.
Applied Optics 05/2004; 43(12):2561-7. · 1.41 Impact Factor
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ABSTRACT: Laser resonator configurations, which enable laser operation with two orthogonally polarized transverse modes, are presented. The intensity distributions of these two modes can be chosen to be complementary, so the gain medium can be exploited more efficiently than with a single mode, leading to improved output power. Moreover, the two modes can be combined and efficiently transformed into a single high-quality beam. Basic principles and experimental results with Nd:YAG lasers are presented.
Applied Optics 07/2002; 41(18):3634-7. · 1.41 Impact Factor
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ABSTRACT: A highly efficient intracavity coherent addition of nine individual laser distributions is presented. It is achieved with two passive interferometric combiners that are introduced into the combined laser cavity. The results reveal that the combined output power is greater by almost a factor of 9 compared to that of the single laser distributions, while the beam quality is the same. © 2006 American Institute of Physics. The potential for high output power concomitantly with good beam quality has led to the development of many meth-ods for phase locking and the coherent addition of lasers over the past several decades. These include evanescent waves coupling, 1,2 Talbot and Fourier transform resonators, 3,4 active feedback control of both cw and ultrafast lasers, 5–7 the introduction of diffractive components and phase elements into the laser resonators, 8–11 Vernier-Michelson resonators, 12,13 and the incorporation of fiber couplers. 14,15 In general two major difficulties must be over-come when performing coherent addition. The first results from the need for proper phase locking which requires very accurate relative alignment between the lasers. The second, and somewhat related difficulty, results from the need to accurately control the relative phase so as to obtain construc-tive interference between the laser distributions. In the past, we demonstrated an approach for efficient coherent addition of two Gaussian laser distributions, using relatively simple intracavity interferometric combiners. 16 The ability to scale this approach in a compact manner to coherently add multiple beam distributions is of great prac-tical importance. Here we extend this approach, to coher-ently add larger arrays of laser distributions, using somewhat more complicated interferometric combiners. Specifically, we first extend the approach in order to obtain efficient co-herent addition using a single sequential interferometric combiner that is designed to deal simultaneously with three laser distributions. This is followed by the coherent addition of nine laser distributions, using two such interferometric combiners that are orthogonally oriented inside the combined laser cavity. Essentially, similar combiners as those intro-duced here can be used to coherently add larger arrays 4 4, 5 5, etc. using only two interferometric combiners, thus enabling compact laser configurations with high output power. The single-substrate interferometric combiner and how it coherently adds three parallel laser beams along a line, is presented in Fig. 1. The interferometric combiner is formed of a high precision plane parallel plate, with specially de-signed coatings. Specifically, a third of the front surface is coated with an antireflection layer, a third with a 50% beam splitter layer, and the remaining third with a 66% reflec-tance beam splitter layer. Two thirds of the rear surface are coated with a highly reflecting layer and the remaining third is coated with an antireflection layer. As shown in Fig. 1, beam 1 enters the interferometric combiner, reflected from the backsurface and intercepts beam 2 at the 50% beam split-ter layer. The reflected part of beam 1 interferes construc-tively with the transmitted part of beam 2, while the remain-ing parts of the two beams interfere destructively towards the direction of loss channel 1a. The combined beam, composed of reflected beam 1 and transmitted beam 2, propagates to-wards the backsurface, where it is reflected and intercepts beam 3 at the 66% beam splitter layer. The reflected part of the combined beam interferes constructively with the trans-mitted part of beam 3, while the remaining parts of the two beams interfere destructively towards the direction of loss channel 2a. The overall combined beam, hence, composed of all three beams, emerges from the output interface of the interferometric combiner. With two such interferometric combiners, oriented orthogonally with respect to each other, a two-dimensional array of nine laser distributions can be coherently added. As is well known, phase locking and coherent addition self-occurs due to the inherent ability of the combined laser resonator to select the mode of operation with minimal losses, but only if all the individual laser distributions have some common longitudinal modes. In general, as the number of laser distributions that must be coherently added in-creases, the probability for obtaining common longitudinal modes may rapidly decrease. 12 Such a decrease is alleviated with our interferometric combiners, whose constant thick-ness ensures that the path difference between sequential laser distributions is always the same.
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ABSTRACT: We investigate configurations for upscaling the number of laser distributions that can be coherently added by means of intra-cavity interferometric combiners. Experimental demonstrations of coherent addition of 5 and 25 laser distributions are presented. Calculated results indicate that with our configurations upscaling to a large number of coherently added distributions is possible but strongly depends on the tolerances of the interferometric combiners.
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ABSTRACT: A new approach for stable intra-cavity phase locking of several laser channels is presented. In this approach, special interferometric couplers are incorporated inside a laser resonator to obtain efficient self phase-locking between separate laser channels. We analyze the approach and demonstrate experimentally phase-locking of two and of four laser channels, that are derived from Nd:YAG lasers, with 92% and 83% power efficiencies respectively.
