基于二向色镜密集光谱合束的高亮度半导体激光研究

Dichroic Mirror Based on Dense Wavelength Combining of High-Brightness Laser Diode

相比常规的二向色镜激光合束,采用窄线宽半导体激光结合薄膜二向色镜进行的密集光谱合束,通道数量显著增多,可以实现高功率、高亮度的半导体激光输出。理论分析了薄膜二向色镜入射角度与中心波长、透过率之间的关系,结果表明:随着入射中心波长增大,入射角度逐渐变小,同时薄膜二向色镜的透射谱随之发生改变。对中心波长为969nm、976nm、981nm的3束半导体激光开展了密集光谱合束实验,实现了输出功率为311.9W、合束效率为95.88%、亮度为58.42MW/(cm^(2)·sr)、子束光谱间隔最大为7nm的合束激光输出,合束激光相比子束的光束质量退化率不大于1.06倍。

Objective The laser diode(LD)has many advantages,such as light weight,high efficiency and high reliability.However,it has disadvantages,such as low power in a single unit,poor beam quality and low brightness,that limit the LD’s application as a direct laser source in industry and national defence.Dichroic mirror spectral beam combination is a common aperture and different wavelength LD beam combing technology based on the super steep,narrow-band and thin-film.This method has advantages of narrow spectral width,stable wavelength,high brightness and compact system,which has been an effective approach for improving LD brightness,output power and spectral characteristics.We started with the Fabry-Perot(F-P)cavity basic theory and analysed the relationship between incident angle and central wavelength or transmission.It provided the basis for beam combing with thin-film and high efficiency dense spectral beam combing.Simultaneously,we were the first in China to conduct a three sub-beam combing experiment based on thin-film with a spectral interval of less than 7 nm.A 311.9 W power was obtained,with a 95.88%beam combing efficiency,a 58.42 MW/(cm^(2),sr)brightness,and a spectral width of 12 nm.We hope that the findings of our study will spur the use of laser deep fusion in welding,cutting,and small mobile platforms.Methods In this letter,we began with the basic theory of an F-P optical cavity,analysed the relationship between thin-film incident angle and central wavelength,as well as transmission.Then,we used different wavelengths of LD to evaluate the thin-film device angle and transmission properties.In addition,the spectrum,power,and efficiency of the sub-beam source were measured in variable current and temperature.Next,we established the dense spectral beam combing platform and conducted experimental research,such as pointing error analysis of near-and far-fields after installation and adjustment.In contrast,we measured the beam combing power and efficiency,as well as the beam quality deterioration before and after combing.Furthermore,we monitored the thin-film device’s heat stability to demonstrate the beam combing system’s stability.The optical path was established through the method of theoretical analysis and experimental demonstration.We can achieve kW level power output in the condition of 10 channel beam combing,according to the design and experiment.In addition,we compared the design to the measurement,and the two agreed well.Results and Discussions The study showed that as the central wavelength increased,the incident angle was smaller(Fig.2),and the transmission spectrum shifted.To achieve beam combing,we used different wavelengths,such as 969,976,and 981 nm,and the transmission was evaluated using the wavelength vs angle curve(Fig.3,Table2).For example,the best incident angle of 969 nm sub-beam is 29.6°,and the angle bandwidth is 0.9°.The spectrum was measured at currents ranging from 1 to 11 A and temperatures ranging from 10°to 30°(Fig.6,Table 3).We studied three sub-beam beams combing with a spectral interval of less than 7 nm and obtained an output power of 311.9 W,a beam combining of 95.88%(Fig.10),a brightness of 58.42 MW/(cm^(2),sr),a spectral width of 12 nm,and a beam quality deterioration was less than 1.06 times(Table.6).The temperature of the thin-film filter(TFF)device ranged from 27℃to 61.5℃with currents ranging from 5 A to 11.5 A(Fig.12).The results show that using TFF beam combing,we can obtain stable and high power output,the efficiency and beam quality deterioration are acceptable,the TFF device can bear high power density,and it has a strong promotion to the high power LD.Conclusions We used dichroic mirror dense spectral beam combing to model and analyse the impact on incident angle,centre wavelength and thin-film transmission.Further,we developed an experimental study on three subbeam combing wavelengths of 969,976,981 nm,achieving an output power of 311.9 W,a beam combining of 95.88%,a brightness of 58.42 MW/(cm^(2),sr),a spectral width of 12 nm,and a beam quality deterioration of less than 1.06 times.Compared to traditional beam combing based on the dichroic mirror,we can decrease the spectral width from several tens of nm to only 7 nm,and the combing channels substantially increased,allowing us to achieve higher brightness and power LD output relatively easily.In addition,when compared with dense spectral beam combing of about 0.5 nm,this type of beam combing has the disadvantages of a wider spectral interval,but this method can play the role of secondary beam combing and the output from dense spectral beam combing can be regarded as sub-beam.These findings are important in terms of increasing the power and brightness of direct diode lasers.