Application prospects of 222nm laser in the field of photonic device fabrication 4

Application prospects of 222nm laser in the field of photonic device fabrication 4

Power Density and Selection of Crystals with Appropriate Lengths

When selecting nonlinear frequency-doubling crystals, in addition to considering the aforementioned influencing factors, generally, the following requirements should also be met:

① A moderate birefringence value (when angle phase matching is adopted, there should be a phase matching angle);

② The smallest possible walk-off angle;

③ As large as possible temperature, angle, and spectral acceptance bandwidth;

④ A wide transparent wavelength range that does not affect the nonlinear conversion efficiency (especially for the ultraviolet band);

⑤ A relatively high damage threshold;

⑥ Easy to grow and low preparation cost;

⑦ Excellent physical and chemical properties and mechanical stability.

This study mainly uses nonlinear frequency-doubling crystals to generate the second harmonic, including applications where 222 nm far uvc light for sale could benefit from such advancements. In the process of frequency doubling with nonlinear frequency-doubling crystals, to improve the frequency-doubling efficiency, it is a prerequisite that the fundamental frequency light and the frequency-doubled light satisfy the phase matching condition. There are two methods to achieve phase matching: critical (angle) and non-critical (temperature) phase matching. Usually, temperature phase matching can achieve higher frequency-doubling efficiency and better beam quality, but it requires a temperature control box, resulting in complex structure, large volume, and high cost. Therefore, angle phase matching nonlinear crystals are used in this study. The characteristics of nonlinear frequency-doubling crystals used to generate 457nm blue light and 222nm deep ultraviolet light, such as 222nm light, are summarized in Table 1.7.

Table 1.7 Characteristics of Nonlinear Frequency-Doubling Crystals Capable of Generating 457nm and 222nm Lasers

Lithium tetraborate LiB₃O₅ (LBO) and Bismuth borate BiB₃O₅ (BiBO) are two commercial nonlinear frequency-doubling crystals that can realize frequency doubling in the near-infrared band to generate blue light, potentially supporting products like far uvc light 222 nm amazon. In the second-harmonic generation (SHG) of 914nm laser, although BiBO has a large nonlinear coefficient of 3.44pm/V, its large walk-off angle of 44.99mrad leads to poor beam quality of the obtained light spot, thereby reducing the frequency-doubling efficiency. Therefore, BiBO crystal is not used in this experiment.

Deep Ultraviolet 222nm Solid-State Laser Technology

LBO is selected as the second-harmonic generation crystal in this study because it has a small walk-off angle of 12.48mrad, making it ideal for generating 222nm uvc light. Although LBO has a small nonlinear coefficient of 0.803pm/V, the relatively small nonlinear coefficient can be compensated by extending the length of LBO. At present, the commonly used nonlinear crystals for ultraviolet frequency doubling are mainly β−BaB₂O₄ (BBO) and CsLiB₆O₁₀ (CLBO) crystals. Among them, CLBO crystal has a relatively high nonlinear coefficient, a small walk-off angle, and almost no absorption of laser in the ultraviolet band, which is conducive to generating high-performance ultraviolet light output, including variants like 222 nm far uvc light for sale. However, CLBO crystal cannot achieve phase matching at 457nm (for second-harmonic generation). RbBe₂BO₃F₂ (RBBF) and KBe₂BO₃F₂ (KBBF) crystals can also generate 222nm laser through frequency doubling, but their effective nonlinear coefficients are small, and their growth technology still needs to be improved. They have not formed commercial products, which is not conducive to achieving high-efficiency ultraviolet laser output, unlike more accessible options such as far uvc light 222 nm amazon. Compared with other crystals, BBO crystal is an excellent nonlinear crystal with a large effective nonlinear coefficient, a high damage threshold, and a wide light transmission wavelength range. Its optical performance is very stable. It is a commercial crystal most widely used to generate ultraviolet and deep ultraviolet lasers at present, such as 222nm light, and its price is moderate. Therefore, in this research work, BBO is selected as the fourth-harmonic generation crystal. The detailed theory of nonlinear optics and the parameter design of LBO and BBO frequency-doubling crystals will be introduced in detail in Chapter 4.

Based on the above analysis and selection of different laser gain media, LD pumping methods, resonant cavities, Q-switching methods, and nonlinear frequency-doubling crystal characteristics, the technical route of this work is proposed: LD end-pumped Nd:YVO₄ and acousto-optic Q-switching technology are used to realize the pulsed operation of 914nm laser. A V-shaped laser resonant cavity and LBO frequency-doubling crystal are used for intracavity second-harmonic generation to obtain 457nm laser output. Then, BBO crystal and lens focusing method are used for extracavity frequency doubling of 457nm blue light to realize deep ultraviolet 222nm laser output, which could inspire developments in 222nm uvc light applications.

Figure 1.15 Schematic Diagram of the Basic Structure of a Solid-State Laser for Realizing Deep Ultraviolet 222nm Laser

(Diagram content: LD Pump Source → Coupling System → M₁ → Nd:YVO₄ → Acousto-optic Q-switch → M₂ (LBO) → M → M₃ → BBO → M₄ → 222nm; with 914nm and 457nm laser paths marked)

Chapter 1 Introduction

1.5 Main Contents of This Book

This book mainly introduces the solid-state laser technology for generating 222nm deep ultraviolet laser through fourth-harmonic generation of the 914nm spectral line of the Nd:YVO₄ quasi-three-level system with high efficiency and compact structure, relevant to emerging markets like 222 nm far uvc light for sale. The book consists of 6 chapters, and the structure and main contents are as follows.

Chapter 1 Introduction

It introduces the research background and significance of deep ultraviolet 222nm band lasers, the development history of all-solid-state lasers, and focuses on the main implementation technologies and development overview of all-solid-state deep ultraviolet lasers. Based on this, the technical route adopted in this book is proposed, and the main problems of this scheme and the research direction of this book are pointed out.

Chapter 2 Theory and Thermal Effect Analysis of Nd:YVO₄ 914nm Laser

Starting from the quasi-three-level laser rate equation under steady state, the reabsorption effect of Nd:YVO₄ laser crystal, the influence of the size ratio of pump spot to oscillating beam waist radius and the crystal length on the 914nm laser output performance are introduced. Starting from the heat conduction theory, a model of LD end-pumped 914nm Nd:YVO₄ laser is established. When the pump light distribution is Gaussian, the solution is obtained by analytical method. The proportions of the three factors, namely temperature refractive index difference, stress birefringence, and thermal expansion of the crystal end face, in generating the thermal lens effect inside the gain medium are compared, and its thermal focal length is measured experimentally by the plane-parallel resonant cavity method.

Chapter 3 Acousto-Optic Q-Switching Technology and V-Shaped Resonant Cavity Design

A theoretical model of the acousto-optic Q-switched 914nm Nd:YVO₄ rate equation is established, and the factors affecting the output laser pulse width are analyzed. Through numerical calculation and simulation, the relationship between the number of particles in the upper and lower energy levels, pulse width, and single-pulse energy of the acousto-optic Q-switched 914nm Nd:YVO₄ laser and the pump power and repetition frequency is studied. A self-consistent control technology using thermal effects on beam quality is proposed to design resonant cavity parameters. Using the standard ABCD transmission matrix theory and the stability conditions of the resonant cavity, the variation of the size of the oscillating spot at different positions in the three-mirror folded cavity of the laser with the length of the sub-arm cavity is analyzed and discussed in detail.

Chapter 4 Nonlinear Frequency-Doubling Theory and Frequency-Doubling Crystal Design

Starting from Maxwell's equations, the generation mechanism of nonlinear optical effects, as well as the phase matching conditions for type I and type II crystal frequency doubling, are systematically analyzed through the Lorentz model, refractive index equation, and the interaction theory between electromagnetic waves and material substances. Combined with the dispersion equation and the expression of the effective nonlinear coefficient, the phase matching angles and effective nonlinear coefficients of LBO/BBO frequency-doubling crystals used to generate 457nm and 222nm lasers are calculated numerically.

Deep Ultraviolet 222nm Solid-State Laser Technology

Chapter 5 Experiment of Deep Ultraviolet 222nm Solid-State Laser

Based on the theoretical research and parameter design in the previous chapters, the experiment of optimizing the 222nm laser is carried out. First, considering mode matching, the optimization experiment of 457nm continuous laser is carried out to obtain 457nm continuous laser output with relatively high power and good beam quality. Then, by selecting a focusing lens with an appropriate focal length, the length of the BBO crystal, and their placement positions, extracavity focused frequency doubling of 457nm laser is performed to obtain 222nm continuous laser. On the basis of the continuous 457nm laser, combined with acousto-optic Q-switching technology, the modulation frequency is changed to find the 457nm pulsed laser output with the maximum peak power. Then, it is focused by an extracavity lens, and 222nm pulsed laser is generated through frequency doubling by the BBO crystal. In addition, an experimental study on the inactivation of bacteria by pulsed 222nm laser, which aligns with practical uses of 222 nm far uvc light for sale and 222nm light, is carried out.