1.73微米高重复率电光调Q光学参量振荡器的研究

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"这篇论文介绍了一种基于钾钛酸钡的电光调Q开关的高重复频率1.73微米光学参量振荡器(OPO)，实现了在1729.4纳米波长的最大输出功率1.56瓦，原始基频激光功率5.48瓦。该激光器产生的脉冲宽度为11.22纳秒，重复频率500赫兹时，脉冲能量超过3毫焦耳，据作者所知，这是在1.73微米波段运行的OPO激光器中，能量输出最高的，达到了100赫兹数量级。这种激光器主要用于深度组织的选择性成像，是活体患者易损斑块诊断的一种有前景的方法。" 这篇论文详细探讨了电光调Q技术在高重复频率1.73微米光学参量振荡器中的应用。光学参量振荡器（OPO）是一种非线性光学设备，能够将输入的激光能量转换到不同的波长，实现宽带光谱覆盖。在本研究中，OPO基于钾钛酸钡（KTP）晶体，这是一种常见的非线性光学材料，因其高效的二次谐波生成和四波混频特性而广泛用于光谱学和激光技术。论文中提到的关键点包括： 1. **电光调Q开关技术**：这是一种控制激光脉冲质量和能量的技术，通过改变激光腔内的折射率来实现对激光脉冲的快速开关。在本文中，电光调Q使得OPO能够产生高能量、短脉宽的脉冲，这对于某些应用如医学成像至关重要。 2. **高重复频率**：500赫兹的重复频率意味着激光器能够在每秒内产生500个脉冲，这为连续操作提供了足够的脉冲密度，同时保持了较高的单脉冲能量。 3. **输出功率和脉冲能量**：1729.4纳米处的最大输出功率1.56瓦和单脉冲能量3毫焦耳的结合，表明该OPO在1.73微米波段具有卓越的性能。这在同类设备中是前所未有的，提升了该波长激光器的潜力。 4. **应用领域**：由于1.73微米波长的光可以穿透生物组织，因此这种激光器特别适用于深度组织成像，尤其是活体患者的易损斑块诊断。易损斑块是指可能导致心脏病或中风的动脉斑块，早期检测和诊断对于预防心血管疾病非常重要。这篇论文展示了电光调Q开关技术在提高1.73微米OPO性能方面的成功尝试，以及其在生物医学领域的潜在应用价值。这一创新可能为未来的医疗成像和治疗提供更有效、更精确的工具。

Electro-optically Q-switched high-repetition-rate

1.73 μm optical parametric oscillator

Qianhuan Yu (喻乾桓)

1,2

, Mingjian Wang (王明建)

*, and Weibiao Chen (陈卫标)

Key Laboratory of Space Laser Communication and Detection Technology, Shanghai Institute of Optics and

Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China

University of Chinese Academy of Science, Beijing 100049, China

*Corresponding author: wmjian@siom.ac.cn; **corresponding author: wbchen@mail.shcnc.ac.cn

Received February 11, 2015; accepted May 15, 2015; posted online July 7, 2015

We demonstrate a potassium titanyl phosphate-based optical parametric oscillator (OPO) emitting at 1729 nm.

A maximum output power of 1.56 W at 1729.4 nm is obtained with an original fundamental laser power of

5.48 W. The pulse with a pulse duration of 11.22 ns exceeds 3 mJ at a 500 Hz repetition rate. To our knowledge

this is the highest energy output of an OPO laser emitting around 1.73 μm operating at a 100 Hz order of mag-

nitude. This laser is primarily used for bond-selective imaging of deep tissue, a promising way for diagnosing

vulnerable plaques in live patients.

OCIS codes: 140.3070, 140.3538, 140.3580, 190.4970.

doi: 10.3788/COL201513.081406.

The generation of lasers radiating in the infrared has

attracted great interest for their important applications

in medical diagnostics, food and agrochemical quality con-

trol, neuroimaging, etc.

[1–4]

. Recent research reveals the

existence of an optical window between 1600 and

1850 nm that makes it promising for deep tissue imaging.

In this optical window lasers radiating around 1730 nm

play an important role for intravascular photoacoustic

imaging, a well-established, hybrid, and most promising

candidate for noninvasive measurement techniques

[5]

High repetition rate nanosecond lasers around 1730 nm

currently are applied to this technique. However, this im-

aging technique has been stifled by its slow imaging speed,

which mainly depends on the repetition rate of the pulse

[6]

As higher pulse repetition will make the imaging system

work faster, this tissue imaging technique calls for a laser

emitting around 1730 nm with a high pulse repetition rate.

Traditionally it is possible to obtain a laser emitting at

1730 nm directly by pumping an Er:YLF crystal

[7]

Doroshenko et al. have already adopted a flashlamp-

pumped Er:YLF laser with a quasi-continuous output

of more than 800 mJ

[8]

. Barnes et al. have reported a

Q-switched Er:YLF laser with a pulse energy of 25 mJ

pumped by a flashlamp. The repetition of the pulse in

the system is limited to 5 Hz. The short wavelength pump

bands of Er:YLF cannot match the commercial laser diode

(LD) emitting waveband, so it is not possible to pump the

crystal with a LD

[9]

. This leads to low power conversion

efficiency. Moreover, higher repetition rates bring a seri-

ous thermal effect while pumped by a Xe flashlamp. Being

pumped by a flashlamp also leads to low power conversion

efficiency. Therefore, it is intractable to obtain a laser

emitting around 1730 nm at a high repetition rate by

using an Er:YLF crystal.

Another way to obtain a 1.73 μm laser is with an optical

parametric oscillator (OPO). In the past few years interest

in efficient eye-safe lasers has stimulated the development

of OPOs

[10–12]

. Since 1995, quasi-phase-matching (QPM)

schemes were also popularly used to obtain infrared laser

radiation

[13]

. This inspired us to make an OPO matching

the demand. Many tunable OPOs already have a tuning

range including 1730 nm. In 2005, Peng et al. reported a

high-repetition-rate tunable OPO with a wide tuning

range from 1650 to 2100 nm

[14]

. Only about 1.5 mJ can

be obtained at 1730 nm. Even some commercial OPO

enterprises such as OPOTEK also have several tunable

products with a tuning range including 1730 nm. How-

ever, either their tunable product operating repetition rate

stays in a ten hertz order of magnitude, such as Opolette

532, or the output energy of their products is not strong

enough for an imaging system such as Opolette HR.

Consequently, these products cannot solve the problem

of accelerating the imaging speed. In order to solve the

problem, a high-power laser working at a high repetition

rate emitting around 1.73 μm needs to be developed.

Here, a potassium titanyl phosphate (KTP)-OPO

driven by a diode-end-pumped Nd:YAG laser emitting

at around 1.73 μm is demonstrated for the first time to

our knowledge. Under a pumping laser power of 5.48 W

and repetition rate of 500 Hz, a maximum average output

power of 1.56 W at 1729.4 nm was obtained, correspond-

ing to an optical-optical conversion efficiency of 28.5%

from an original fundamental laser to a signal laser. A

pulse energy of more than 3 mJ at 500 Hz with a pulse

duration of 11.22 ns was obtained. The output pulse

energy fluctuation supervised by a power meter of

1.73 μm was less than 0.5% during the 2 h operating

period.

A schematic diagram of the experimental setup is

depicted in Fig.

1. Two fiber-coupled LDs with a 30 W

maximum output power emitting at 808 nm were used

as the pump source. The fiber core diameter was

COL 13(8), 081406(2015) CHINESE OPTICS LETTERS August 10, 2015

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