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Sixth Symposium on Novel Optoelectronic Detection Technology and Applications

Violet and blue laser in rubidium four-wave mixing system

Zhen Yang, Wanfa Liu, Shu Hu, Xianglong Cai, Hui Li, Xueyang Li, Xiaohong Zhao, Shihong Wang, Jingwei Guo

Published Apr 17, 2020• 0 citations
Publisher

Abstract

This paper reports the simultaneous output of 358.7nm and 420.3nm laser generated by two-photon excitation (52 S1/2→62 D5/2, TPE) and four-wave mixing effect (FWM) in rubidium system for the first time. Unlike some fluorescent signals, this four-wave mixing beam has a high monochromaticity and extreme directivity and can be used as a laser source. In this study, we also measured the fluorescence lines in the range of 300-820 nm under 52 S1/2→62 D5/2 TPE, and studied other transitions that may occur. The experimental results show that the blue-violet laser produced by this alkali metal rubidium four-wave mixing can provide a new laser source for underwater laser communication, display technology, fluorescence excitation, Raman spectroscopy, marine resource detection, laser biomedicine, lithography, high density information storage and other fields.

DOI
10.1117/12.2563487

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This paper reports the simultaneous output of 358.7nm and 420.3nm laser generated by two-photon excitation (52 S1/2→62 D5/2, TPE) and four-wave mixing effect (FWM) in rubidium system for the first time. Unlike some fluorescent signals, this four-wave mixing beam has a high monochromaticity and extreme directivity and can be used as a laser source. In this study, we also measured the fluorescence lines in the range of 300-820 nm under 52 S1/2→62 D5/2 TPE, and studied other transitions that may occur. The experimental results show that the blue-violet laser produced by this alkali metal rubidium four-wave mixing can provide a new laser source for underwater laser communication, display technology, fluorescence excitation, Raman spectroscopy, marine resource detection, laser biomedicine, lithography, high density information storage and other fields.
We demonstrate the generation of the coherent 420 nm laser via parametric four-wave mixing process in Rb vapor. A single 778 nm laser with circular polarization is directly injected into a high-density atomic vapor, which drives the atoms from the 5S1/2 state to the 5D5/2 state with monochromatic two-photon transition. The frequency up-conversion laser is generated by the parametric four-wave mixing process under the phase matching condition. This coherent laser is firstly certified by the knife-edge method and a narrow range grating spectrometer. Then the generated laser power is investigated in terms of the power and frequency of the incoming beam as well as the density of the atoms. Finally, a 420 nm coherent laser with power of 19 μW and beam quality of M x 2 = 1.32 , M y 2 = 1.37 is obtained with optimal experimental parameters. This novel laser shows potential prospects in the measurement of material properties, information storage, and underwater optical communication.
Blue-violet wavelength multiplexing offers the capability to enhance the operational capacity and efficiency in optical information processing, underwater communications, biology, and medicine. Here we present a specially designed atomic scheme of cesium for simultaneously generating two blue-violet lasers at 456 and 459 nm via four-wave-mixing (FWM)-based upconversion processes. We experimentally and theoretically show that a double-diamond-type coherent system pumped with 852 and 921 nm lasers is responsible for the efficient generation of the two blue-violet lasers. In this system, the large population inversions lead to self-amplified spontaneous emissions at 15.6 and 12.1 µ m , which, in turn, serve as the seeds for enhanced double FWM processes with dual-wavelength upconversions.
The four-wave mixing (FWM) process is an important method for generating collimated blue light from alkali vapor. In this paper, we introduced high-pressure He gas to broaden the absorption linewidth of Rb atoms for the pump laser. By using an optical parametric oscillator (OPO) that outputs tunable wavelength pump laser, we performed two-photon excitation of the Rb-He mixture and achieved redshifted and asymmetric broadened collimated light (CL) around 420 nm. We demonstrated the participation of Rb-He excimers in the FWM process for the first time, to the best of our knowledge, from both spectral and temporal dimensions, and revealed the underlying mechanism. Experiments showed that the peak of the ∼420 nm CL intensity appeared at higher heating temperatures, influenced by changes in the optical depth of the Rb-He mixture. This study provides both theoretical and experimental support for the promotion of a collimated blue light scheme in alkali metal -buffer gas systems, balancing the pump laser absorption and FWM efficiency.
We have incorporated a ring cavity to enhance the efficiency of parametric four-wave mixing in rubidium (Rb). Using an input coupler with 95% reflectance, a finesse of 19.6±0.5 is achieved with an Rb cell inside. This increases the circulating intensity by a factor of 5.6±0.5, and through two-photon excitation on the 5s1/2→5d5/2 transition with a single excitation laser, up to 1.9±0.3 mW of power at 420 nm is generated, 50 times what was previously generated with this scheme and comparable to low-power two-step excitation. The dependence of the output on the Rb density and input power has been explored, suggesting the process may be approaching saturation. The blue output of the cavity also shows greatly improved spatial quality, combining to make this a promising source of 420 nm light for future experiments.
Achieving population inversion through multi-photon cascade pumping is almost always difficult, and most laser medium work under 1-photon excitation mechanism. But for alkali atoms such as cesium, relatively large absorption cross sections of several low, cascading energy levels enable them properties such as up conversion. Here we carried out research on two-photon excitation alkali fluorescence. Two photons of near infrared region are used to excite alkali atoms to n 2 D5/2, n 2 D3/2 or higher energy levels, then the blue fluorescence of (n+1) 2 P3/2,(n+1) 2 P1/2→n 2 S1/2 are observed. Different pumping paths are tried and by the recorded spectra, transition routes of cesium are deducted and concluded. Finally the possibility of two-photon style DPALs (diode pumped alkali laser) are discussed, such alkali lasers can give output wavelengths in the shorter end of visual spectroscopy (400-460 nm) and are expected to get application in underwater communication and material laser processing.
Four-wave mixing can be used to generate coherent output beams, with frequencies difficult to acquire in commercial lasers. Here, a single narrow external cavity diode laser locked to the two photon 5s-5d transition in rubidium is combined with a tapered amplifier system to produce a high power cw beam at 778 nm and used to generate coherent light at 420 nm through parametric four-wave mixing. This process is analyzed in terms of the intensity and frequency of the incoming beam as well as the atomic density of the sample. The efficiency of the process is currently limited when on resonance due to the absorption of the 420 nm beam, and modifications should allow a significant increase in output power.