Low Noise Intracavity Frequency Doubling Yellow Green Laser at 556 nm Based on Ti3C2Tx-PVA Passively Q-switching
The low noise yellow-green laser at 556 nm has a wide range of applications in industries such as industrial,atmospheric remote sensing,communications,information storage,as well as in fields like food and drug detection.However,it is necessary to suppress the two spectral lines at 1 116 nm and 1 123 nm,which are close in wavelength and have similar stimulated emission cross-sections to each other,in order to ensure the oscillation of the fundamental frequency light at 1 112 nm in the cavity and achieve low noise frequency-doubled yellow-green laser at 556 nm.The conventional adoption of the F-P standard leads to considerable insertion loss,which markedly raises the oscillation threshold of the fundamental frequency light at 1 112 nm.As a consequence,the frequency-doubling efficiency and output power of the yellow-green laser at 556 nm are compromised,and there is a risk of the 1 112 nm fundamental frequency light failing to oscillate.When using a Birefringent Crystal(BC),precise adjustments of the Brewster angle of the BC,the angle between the BC surface and the optical axis of the cavity,and the phase-matching angle of the frequency-doubling crystal,are all typically required simultaneously.This intricate multidimensional angle tuning often presents formidable challenges in achieving a low noise yellow-green laser at 556 nm.In recent years,titanium carbide Ti3C2Tx has garnered significant attention in passive Q-modulated laser research due to its controllable energy band structure,wide range of nonlinear optical response,large nonlinear absorption coefficient,and high damage threshold.However,the current literature on Ti3C2Tx as a Saturable Absorber(SA)mainly revolves around 1.06 μm,1.3 μm,2.73 μm,and 3 μm laser wavelengths.To date,there has been no report on utilizing Ti3C2Tx for passively Q-switching of a yellow-green laser at 556 nm.The low noise passively Q-switched yellow-green laser at 556 nm is achieved through a technical approach that incorporates an 808 nm Laser Diode(LD)end-pumped Nd:YAG ceramic,a Ti3C2Tx-PVA film passively Q-switching,collaborative frequency selection and filtering with a Brewster Polarizer(BP)and a BC,as well as intra-cavity frequency doubling with a critical phase-matched type-I LBO crystal.The synergistic use of BP and BC not only ensures that only the p-polarised light at 1 112 nm achieves oscillation and amplification in the cavity,but also reduces the number of longitudinal modes at 1 112 nm,which results in the filtering of the fundamental frequency light at 1 112 nm and noise reduction of the frequency-doubled yellow-green laser at 556 nm.Using a liquid phase stripping and a spin coating methods,the Ti3C2Tx-PVA film containing 3～4 layers of Ti3C2Tx nanosheets with saturated light intensity and modulation depth near 1 μm wavelength of 2.12 MW/cm2 and 6.35%,respectively,was experimentally prepared.A passively Q-switched yellow green laser at 556 nm with Ti3C2Tx PVA thin film as SA was obtained.At 5.11 W LD pump power,the maximum average power,maximum repetition frequency,and narrowest pulse width of the yellow green laser at 556 nm were 86.2 mW,745.8 kHz,and 46 ns,respectively,with the power instability and the laser noise only at±0.39%and 0.37%in 4 h,respectively.Meanwhile,the beam quality factors were M2x = 1.837,M2y = 1.975.The results of power instability and laser noise of±0.39%and 0.37%in 4 h show that the synergistic utilization of BP induces BC to exhibit greater reflective losses for the 1 116 nm and 1 123 nm spectral lines,thereby further enhancing the cavity's suppression capability towards these two lines.Considering the adopted thermal management measures,an average power of 86.2 mW,a repetition frequency of 745.8 kHz and a pulse width 46 ns also demonstrates the excellent operational reliability of the Ti3C2Tx-PVA film as SA from another perspective.In summary,the combined use of BP and BC not only ensures that only the 1 112 nm laser oscillates in the cavity,but also reduces the number of longitudinal modes in the 1 112 nm laser,thereby achieving filtering and noise reduction in the frequency doubling yellow green laser at 556 nm."Ti3C2Tx-PVA film passively Q-switching combined with synergistic frequency selection and filtering using BP+BC"is an effective method for obtaining high stability and low noise yellow-green pulsed lasers.This method can provide high quality yellow-green pulsed laser sources for fields such as biomedical,laser measurement,pollution monitoring and spectral analysis.
Passively Q-switchingTi3C2Tx-PVALow noiseYellow-green laser at 556 nmFrequency selection and filtering
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