CNT-SA激光器：亚纳米高峰值功率脉冲特性研究

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"这篇研究论文探讨了在双量子消薄(Nd:Lu0.15Y0.85VO4)激光器中，利用不同壁结构的碳纳米管(CNTs)实现高峰值功率亚纳秒脉冲特性。通过同时采用电光调制器和CNT饱和吸收体，在双量子开关和模式锁定(QML)激光器中首次产生了具有高峰值功率的亚纳秒单模锁模脉冲。实验中，研究人员使用了单壁CNTs(SWCNTs)、双壁CNTs(DWCNTs)和多壁CNTs(MWCNTs)作为饱和吸收体，以研究不同的CNT结构对单模锁模脉冲特性的影响。在10.72W的泵浦功率下，观察到了显著的结果。" 这篇论文详细介绍了在激光技术领域的一个创新成果，即通过结合电光调制器和碳纳米管饱和吸收体（CNT-SA）在双重量子开关和模式锁定的掺Nd:Lu0.15Y0.85VO4激光器中产生的亚纳秒脉冲特性。这种激光器工作在1.06微米波长，能产生高峰值功率的脉冲，并且首次实现了在量子开关包络下的单模锁模。碳纳米管因其独特的物理性质，如高非线性光学响应和快速响应时间，常被用作激光器中的饱和吸收体，以实现模式锁定。在这项研究中，科研人员使用了三种不同壁结构的CNTs，分别是单壁、双壁和多壁，以此探究它们如何影响激光器的脉冲特性。这些不同结构的CNTs在激光系统中的应用，可以调整和优化激光器的性能，如脉冲宽度、重复频率和峰值功率。在实验过程中，当泵浦功率达到10.72W时，他们观察到了显著的亚纳秒脉冲输出。这表明，通过调整CNT的壁结构，可以有效地控制激光脉冲的特性和质量，从而可能在各种应用中，如精密测量、光纤通信和医学成像等领域，提高激光器的性能。此外，这项工作还强调了同步使用电光调制器和CNT-SA在双量子损失调制器中的重要性，这种方法能够产生更短的脉冲和更高的峰值功率，这对激光技术的发展具有重要意义。该研究不仅提供了新的设计思路，也展示了对现有激光器技术的改进，对于未来激光科学和技术的研究具有深远的影响。

High peak power subnanosecond pulse characteristics

with different wall structured CNTs in a doubly

QML Nd:Lu

0.15

0.85

laser

Wenjing Tang, Jia Zhao, Kejian Yang, Shengzhi Zhao,* Guiqiu Li, Dechun Li, Tao Li, and Wenchao Qiao

School of Information Science and Engineering, Shandong University, 27 Shanda South Road, Jinan 250100, China

*Corresponding author: shengzhi_zhao@sdu.edu.cn

Received October 20, 2016; revised December 7, 2016; accepted December 8, 2016;

posted December 9, 2016 (Doc. ID 279038); published January 9, 2017

By simultaneously employing both an electro-optic modulator and carbon nanotube saturable absorber (CNT-SA)

in a dual-loss modulator, a subnanosecond single mode-locking pulse underneath a Q-switched envelope with

high peak power was generated from a doubly Q-switched and mode-locked (QML) Nd:Lu

0.15

0.85

laser at

1.06 μm for the first time, to our knowledge. CNTs with different wall structures—single-walled CNTs (SWCNTs),

double-walled CNTs (DWCNTs), and multi-walled CNTs (MWCNTs)—were used as SAs in the experiment to in-

vestigate the single mode-locking pulse characteristics. At pump power of 10.72 W, the maximum peak power of

OCIS codes: (140.3518) Lasers, frequency modulated; (140.3538) Lasers, pulsed; (140.3580) Lasers,

solid-state; (140.4050) Mode-locked lasers.

https://doi.org/10.1364/PRJ.5.000046

1. INTRODUCTION

Stable pulsed lasers with high peak power and short pulse du-

ration have attracted much interest in the fields of laser mea-

surement, nonlinear optics, micromachining processes, and

so on [1–4]. To date, the most common approach to produce

ultrashort pulses is the passive continuous wave (CW) mode-

locking method based on saturable absorption [5]. However,

most of the reported CW mode-locking lasers have a high rep-

etition rate of up to megahertz or even gigahertz, which is ad-

justed only by changing the cavity length. The high repetition

rate could further lower the per-pulse energy and limit the ap-

plication fields of CW mode-locking lasers. In fact, pulses with

manageable low repetition rate and high pulse energy are

needed in some applications, such as fluorescence lifetime

measurement [1], chemical analysis based on laser ablation

[3], and laser micromachining [4]. Thus, in order to generate

short pulses with high peak power and optional low repetition

rate, the dual-loss-modulation Q-switched and mode-locked

(QML) technology is employed [6,7]. By simultaneously using

an active modulator and a saturable absorber (SA) in a laser

resonator, the dual-loss-modulated QML regime can appa-

rently compress the duration of the Q-switched envelope. The

repetition frequency of the mode-locking pulses underneath

the Q-switched envelope is related to the cavity round-trip

transit time. When the pulse width of the Q-switched envelope

is compressed to be shorter than the cavity round-trip trans-

mit time, only one subnanosecond mode-locked pulse in a

Q-switched envelope exists [8]. In this case, the repetition rate

of the single mode-locking pulse will equal that of the active

modulator. In such way, a stable subnanosecond single

mode-locking pulse with low repetition rate and high peak

power can be realized.

In comparison to the active modulator, the role of an SA for

pulse duration compression is more pronounced due to its fast

loss modulation inside the cavity. Therefore, it is important to

choose an excellent SA. In recent years, carbon nanotubes

(CNTs), as an excellent SA, have been successfully employed

in various lasers to generate ultrashort pulses [9–15]. In

comparison with the conventional semiconductor SA (e.g.,

SESAM), CNT-based SAs offer excellent performance with

the advantages of broad absorption spectra (0.8–2.1 μm),

ultrafast recovery time, chemical stability, high optical damage

threshold, and ease of manufacture [9,13,14]. In accordance

with the wall number, CNTs can be divided into single-

walled CNTs (SWCNTs), double-walled CNTs (DWCNTs),

and multi-walled CNTs (MWCNTs) [11,12,16]. To date,

an MWCNT-based dual-loss-modulation subnanosecond

single mode-locking Nd:Lu

0.5

∕KTP green laser has been

demonstrated [17]. However, subnanosecond single mode-

locked lasers at 1.06 μm have not been reported until now,

to our knowledge. Moreover, there is great interest in investi-

gating the subnanosecond single mode-locking pulse charac-

teristics versus CNTs with different wall structures.

In this paper, diode-pumped dual-loss-modulated QML

Nd:Lu

0.15

0.85

lasers at 1.06 μm with an electro-optic (EO)

modulator and different CNT-SAs were presented. To get

a higher pulse energy and shorter pulse duration, a mixed

crystal Nd:Lu

0.15

0.85

was used as the gain medium for

its large energy storage capacity, broad gain spectrum, and

small stimulated emission cross section [18]. An EO modula-

tor was chosen as the active modulator owing to its fast

switching and excellent hold-off ability, which was beneficial

to obtaining a shorter pulse duration of the Q-switched

envelope. By accurately designing the cavity parameters,

a subnanosecond pulse with high stability, high peak

46 Photon. Res. / Vol. 5, No. 1 / February 2017 Tang et al.

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