四束输出被动Q开关Nd:YAG/Cr4+:YAG复合激光器

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"High-peak-power passively Q-switched Nd:YAG/Cr4+:YAG composite laser with multiple-beam output" 这篇论文介绍了一种新型的半导体泵浦的高峰值功率被动Q开关Nd:YAG/Cr4+:YAG复合单晶激光器，该激光器具有四束独立可调焦的输出。这种激光设备的研发与性能测试表明，其脉冲能量超过3毫焦耳，脉冲持续时间为0.9纳秒，具备了选择每束光束焦点的独立能力。 Nd:YAG/Cr4+:YAG复合材料是该激光器的核心，其中Nd:YAG（掺钕钇铝石榴石）是常用的固体激光材料，而Cr4+:YAG则作为Q开关。Q开关是一种控制激光器输出脉冲能量和频率的技术，通过改变激光谐振腔内的损耗，实现短脉冲、高能量的激光输出。在被动Q开关模式下，无需外部电子设备，而是利用非线性光学效应来控制激光的发射，这通常涉及到在激光介质中引入吸收物质，当激光达到一定强度时，吸收物质的吸收状态发生改变，从而触发激光的快速释放。该系统的设计独特之处在于其多束输出功能，允许四束激光独立聚焦，这在实际应用中具有显著优势。例如，在汽车汽油发动机的多点点火中，可以同时激发多个燃烧点，提高燃油效率和发动机性能。此外，这种激光器也可能在空间推进或航空学中的湍流环境中用于点火，因为它可以精确控制每个点火点的能量和位置。文章还提到了接收、修订和发布的时间，表明这是一项2016年的研究工作，且已由Chinese Laser Press出版。OCIS代码揭示了这篇论文涉及的主题，包括固态激光器和钕离子激光器，这些都是激光科学和技术领域的关键领域。这篇研究论文展示了高峰值功率、被动Q开关的Nd:YAG/Cr4+:YAG复合激光器的技术细节，尤其是其多束输出和独立调焦的能力，这些特性使其在汽车工程和空间科技等领域有潜在的应用价值。通过深入研究和优化，这种激光技术有望推动相关行业的发展和创新。

High-peak-power passively Q-switched Nd:YAG/Cr

:YAG

composite laser with multiple-beam output

T. Dascalu, G. Croitoru, O. Grigore, and N. Pavel*

National Institute for Laser, Plasma and Radiation Physics, Laboratory of Solid-State Quantum Electronics,

Magurele, Ilfov, Bucharest 077125, Romania

*Corresponding author: nicolaie.pavel@inflpr.ro

Received July 26, 2016; revised September 25, 2016; accepted September 26, 2016;

posted September 28, 2016 (Doc. ID 272440); published October 21, 2016

We report on the design, realization, and output performance of a diode-pumped high-peak-power passively

Q-switched Nd:YAG∕Cr

4

:YAG composite medium monolithic laser with four-beam output. The energy of a

laser pulse was higher than 3 mJ with duration of 0.9 ns. The proposed system has the ability to choose inde-

pendently the focus of each beam. Such a laser device can be used for multipoint ignition of an automobile

gasoline engine, but could also be of interest for ignition in space propulsion or in turbulent conditions specific

OCIS codes: (140.3580) Lasers, solid-state; (140.3530) Lasers, neodymium; (140.3540) Lasers, Q-switched;

(140.5560) Pumping.

http://dx.doi.org/10.1364/PRJ.4.000267

1. INTRODUCTION

Ignition induced by laser is currently viewed as an alternative

technique to ignition realized by a spark plug, especially for

vehicles with internal combustion engines [1–4]. Among the

advantages of this new ignition method, one could mention:

(i) the absence of the quenching effect of the developing flame

kernel due to the lack of a spark plug electrode, resulting in

a shorter burn duration; (ii) the possibility to ignite at an op-

timal position into the engine chamber for efficient combus-

tion; (iii) lowering fuel consumption and decreasing exhaust

gas emissions under conditions of normal engine operation,

i.e., near the stoichiometric air–fuel ratio, or (iv) the possibil-

ity to ignite lean air –fuel mixtures and thus to further reduce

engine impact on the environment.

ACO

laser was used to obtain in 1978, for the first time, the

ignition by laser of a single-cylinder engine [5]. Furthermore,

a four-cylinder engine was ignited, in 2008, by a Q-switched

Nd:YAG laser [6]. Because of the experimental conditions,

the bulky lasers were placed outside of the engines and the

laser beams were directed into the engine cylinders by

adequate optics.

A solution for realization of a compact spark-like laser

device was proposed in 2007 by Kofler et al. [7]. Thus, it

was shown that a Nd:YAG laser medium that is passively

Q-switched by a Cr

4

:YAG crystal with saturable absorption

(SA) can deliver pulses with few-millijoule energy and nano-

second-order duration, suitable for laser ignition. The first

high-peak-power passively Q-switched Nd:YAG-Cr

4

:YAG

spark-plug laser was realized in 2010 by Tsunekane et al.

[8]; furthermore, the same research group has investigated

the characteristics of a Yb:YAG-Cr

4

:YAG discrete media

combination for laser ignition applications [9]. Several other

approaches, like the passively Q-switched diffusion-bonded

Nd:YAG∕Cr

4

:YAG laser with wedged Cr

4

:YAG SA [10]

or the diffusion-bonded Nd:YAG∕Cr

4

:YAG laser pumped

laterally through a YAG prism [11], could also be considered

and optimized in order to be used for ignition by a laser. It is

worth mentioning that the majority of these lasers were

pumped longitudinally with fiber-coupled diode lasers. On the

other hand, side pumping with a diode array enabled the reali-

zation of a high-energy Nd:YAG-Cr

4

:YAG laser (the so-called

HiPoLas laser) [12 ]; the same pumping scheme was employed

to build a passively Q-switched Nd:YAG-Cr

4

:YAG pulse-burst

laser for laser ignition [13].

For the first time, in 2013 an automobile gasoline engine

was ignited with only laser sparks by Taira et al. [14].

Recently, we have also operated a four-cylinder engine with

laser sparks [15]. Measurements at average speeds (below

2.000 rpm) concluded that ignition by laser improves engine

stability and decreases emission of CO and HC in comparison

with the same engine that was ignited by classical spark

plugs. In these experiments, laser sparks that were built with

diffusion-bonded Nd:YAG∕Cr

4

:YAG composite media and

that delivered single-beam output have been used [14,15].

On the other hand, a laser offers the possibility to obtain igni-

tion at multiple points, thus better and more uniform combus-

tion in comparison with ignition by electrical spark plugs. For

example, increased pressure and shorter combustion time

were measured for laser ignition in two points of CH

∕air

and H

∕air mixtures in a static chamber [16]. Also, experi-

ments realized with H

∕air mixtures (in a static chamber) con-

cluded that ignition at two points assures faster combustion

in comparison with single-point ignition [17].

To generate multiple points of ignition, several solutions

have been proposed. Thus, end pumping with three inde-

pendent lines of a passively Q-switched diffusion-bonded

Nd:YAG∕Cr

4

:YAG composite ceramic medium allowed

realization of the first spark-plug-like laser device with three

focusing points, at fixed locations [18]. In another approach, a

spatial light modulator was applied to a single laser beam to

Dascalu et al. Vol. 4, No. 6 / December 2016 / Photon. Res. 267

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