Using Femtosecond Laser Light to Investigate the Concentration- and Size-Dependent Nonlinear Optical Properties of Laser-Ablated CuO Quantum Dots

Abstract

In this work, the nonlinear optical (NLO) properties of CuO nanoparticles (CuO NPs) were studied experimentally using the pulsed laser ablation (PLA) technique. A nanosecond Nd: YAG laser was employed as the ablation excitation source to create CuO NPs in distilled water. Various CuO NPs samples were prepared at ablation periods of 20, 30, and 40 min. Utilizing HR-TEM, the structure of the synthesized CuO NPs samples was verified. In addition, a UV-VIS spectrophotometer was used to investigate the linear features of the samples. The Z-scan technique was utilized to explore the NLO properties of CuO NPs samples, including the nonlinear absorption coefficient (β) and nonlinear refractive index (n2). An experimental study on the NLO features was conducted at a variety of excitation wavelengths (750-850 nm), average excitation powers (0.8-1.2 W), and CuO NPs sample concentrations and sizes. The reverse saturable absorption (RSA) behavior of all CuO NPs samples differed with the excitation wavelength and average excitation power. In addition, the CuO NPs samples demonstrated excellent optical limiters at various excitation wavelengths, with limitations dependent on the size and concentration of CuO NPs.

Keywords: copper nanoparticles; femtosecond laser; high repetition rate; nonlinear absorption; nonlinear optics; nonlinear refraction; optical limiter; quantum dots.

Figure 1

Schematic preview of the pulsed laser ablation process for synthesizing CuO NPs via a nanosecond Nd: YAG pulsed laser.

Figure 2

The size distribution of the CuO NPs ablated by the nanosecond Nd: YAG Laser (a) LAT = 20 min, (b) = 30 min, and (c) LAT = 40 min.

Figure 3

The laser ablation time (LAT) of the CuO NPs is a function of both the total surface area (left x-axis) and the number of particles per gram (right x-axis).

Figure 4

Molar concentration of CuO NPs determined via ICP–OES at different laser ablation times (LATs).

Figure 5

The linear absorption spectra of the three CuO NPs samples at LAT = 20, 30 and 40 min.

Figure 6

Energy band gap of the CuO NPs samples at different LATs.

Figure 7

The experimental setup of the Z-scans: A, attenuator; L, convex lens; S, CuO NPs sample; BS, beam splitter; I, iris; PM, power meter.

Figure 8

Open-aperture (OA) Z-scan measurements for different CuO NPs samples at a constant excitation wavelength of 800 nm: (a) LAT = 20 min, (b) LAT = 30 min and (c) LAT = 40 min.

Figure 9

Effect of average power $P_{avg}$ on the NLA coefficient at a constant excitation wavelength of 800 nm: (a) NLA coefficient as a function of average CuO NPs average size and (b) NLA coefficient as a function of the CuO NPs concentration.

Figure 10

Open-aperture (OA) Z-scan measurements for different CuO NPs samples at a constant average power of 1 W: (a) λ = 750 nm, (b) λ = 800 nm and (c) λ = 850 nm.

Figure 11

The effect of the excitation wavelength on the NLA coefficient at a constant average power of 1 W: (a) NLA coefficient as a function of the average size of CuO NPs and (b) NLA coefficient as a function of the CuO NPs concentration.

Figure 12

Closed-aperture (CA) Z-scan measurements for different ablation times of the CuO NPs samples at a constant excitation wavelength of 800 nm: (a) LAT = 20 min, (b) LAT = 30 min and (c) LAT = 40 min.

Figure 12

Closed-aperture (CA) Z-scan measurements for different ablation times of the CuO NPs samples at a constant excitation wavelength of 800 nm: (a) LAT = 20 min, (b) LAT = 30 min and (c) LAT = 40 min.

Figure 13

Variations in the nonlinear refractive indices of the CuO NPs samples at a constant excitation wavelength of 800 at LAT = 20 min, LAT = 30 min and LAT = 40 min.

Figure 14

The dioptric power of the Kerr lens as a function of different average powers for LAT = 20 min, LAT = 30 min, and LAT = 40 min.

Figure 15

Optical limiter behavior of the CuO NPs sample (a) LAT = 20 min, (b) LAT = 30 min, and (c) LAT = 40 min.

Figure 15

Optical limiter behavior of the CuO NPs sample (a) LAT = 20 min, (b) LAT = 30 min, and (c) LAT = 40 min.