Department of Applied Physics and Chemistry and Institute for Laser Science, University of Electro-Communications, Chofugaoka 1-5-1, Chofu, Tokyo 182-8585, Japan.
Sensors (Basel). 2010;10(5):4296-341. doi: 10.3390/s100504296. Epub 2010 Apr 29.
We have reviewed the generation and amplification of wavelength-tunable multicolored femtosecond laser pulses using cascaded four-wave mixing (CFWM) in transparent bulk media, mainly concentrating on our recent work. Theoretical analysis and calculations based on the phase-matching condition could explain well the process semi-quantitatively. The experimental studies showed: (1) as many as fifteen spectral up-shifted and two spectral down-shifted sidebands were obtained simultaneously with spectral bandwidth broader than 1.8 octaves from near ultraviolet (360 nm) to near infrared (1.2 μm); (2) the obtained sidebands were spatially separated well and had extremely high beam quality with M(2) factor better than 1.1; (3) the wavelengths of the generated multicolor sidebands could be conveniently tuned by changing the crossing angle or simply replacing with different media; (4) as short as 15-fs negatively chirped or nearly transform limited 20-fs multicolored femtosecond pulses were obtained when one of the two input beams was negatively chirped and the other was positively chirped; (5) the pulse energy of the sideband can reach a μJ level with power stability better than 1% RMS; (6) broadband two-dimensional (2-D) multicolored arrays with more than ten periodic columns and more than ten rows were generated in a sapphire plate; (7) the obtained sidebands could be simultaneously spectra broadened and power amplified in another bulk medium by using cross-phase modulation (XPM) in conjunction with four-wave optical parametric amplification (FOPA). The characterization showed that this is interesting and the CFWM sidebands generated by this novel method have good enough qualities in terms of power stability, beam quality, and temporal features suited to various experiments such as ultrafast multicolor time-resolved spectroscopy and multicolor-excitation nonlinear microscopy.
我们已经回顾了在透明体中通过级联四波混频（CFWM）产生和放大波长可调谐多色飞秒激光脉冲的方法，主要集中在我们最近的工作上。基于相位匹配条件的理论分析和计算可以对该过程进行半定量解释。实验研究表明：（1）从近紫外（360nm）到近红外（1.2μm），获得了多达十五个上移的光谱边带和两个下移的光谱边带，光谱带宽大于 1.8 个倍频程；（2）获得的边带空间分离良好，具有极好的光束质量，M(2)因子优于 1.1；（3）通过改变交叉角或简单更换不同的介质，很方便地调节生成的多色边带的波长；（4）当两个输入光束中的一个为负啁啾而另一个为正啁啾时，获得了最短为 15fs 的负啁啾或接近变换极限的 20fs 多色飞秒脉冲；（5）边带的脉冲能量可达微焦耳级，功率稳定性优于 1% RMS；（6）在蓝宝石板中产生了具有多于十个周期列和多于十个行的宽带二维（2-D）多色阵列；（7）通过在另一个体介质中结合交叉相位调制（XPM）和四波光学参量放大（FOPA），可以同时对边带进行光谱展宽和功率放大。特性表明，这是很有趣的，通过这种新方法产生的 CFWM 边带在功率稳定性、光束质量和时间特性方面具有良好的品质，适用于各种实验，如超快多色时间分辨光谱学和多色激发非线性显微镜。
