Mirrorless lasers avoid cavity-pulling effects by generating stimulated emission directly from an atomic gain medium without an optical cavity. However, most superradiant or superfluorescent emissions are transient, limiting their use as steady atom-referenced optical sources. Here, we demonstrate a continuous-wave dual-wavelength mirrorless laser in thermal rubidium vapor. A frequency-stabilized 420 nm laser pumps the 5S1/2→6P3/2 transition and generates directional infrared lasing at 1323 and 1367 nm through the non-cascaded 6S1/2→5P1/2 and 6S1/2→5P3/2 transitions. The emissions exhibit threshold-like pump-power dependence and a near-fundamental transverse mode, supporting CW mirrorless laser in a traveling-wave atomic gain medium. Heterodyne detection gives a 1367 nm linewidth of 32.5 kHz, which is 38 times narrower than the natural linewidth. This work establishes a linewidth-narrowed, cavity-free, atom-referenced dual-wavelength laser platform for precision spectroscopy, optical frequency references, and quantum sensing.Mirrorless lasers avoid cavity-pulling effects by generating stimulated emission directly from an atomic gain medium without an optical cavity. However, most superradiant or superfluorescent emissions are transient, limiting their use as steady atom-referenced optical sources. Here, we demonstrate a continuous-wave dual-wavelength mirrorless laser in thermal rubidium vapor. A frequency-stabilized 420 nm laser pumps the 5S1/2→6P3/2 transition and generates directional infrared lasing at 1323 and 1367 nm through the non-cascaded 6S1/2→5P1/2 and 6S1/2→5P3/2 transitions. The emissions exhibit threshold-like pump-power dependence and a near-fundamental transverse mode, supporting CW mirrorless laser in a traveling-wave atomic gain medium. Heterodyne detection gives a 1367 nm linewidth of 32.5 kHz, which is 38 times narrower than the natural linewidth. This work establishes a linewidth-narrowed, cavity-free, atom-referenced dual-wavelength laser platform for precision spectroscopy, optical frequency references, and quantum sensing.

Applied Physics LettersJul 13, 20260 citations

Physics of New Laser Sources

Neal Broadus Abraham, F. T. Arecchi, Aram Mooradian +1 more

NATO ASI series. Series B : PhysicsJan 1, 198528 citations

Continuous-wave laser absorption spectroscopy of the Thorium-229 nucleus

I. Morawetz, T. Riebner, L. Toscani De Col +17 more

A low-energy nuclear transition in the isotope thorium-229 has been excited in thorium-doped crystals with laser light. This opens the perspective towards a highly stable and robust solid-state optical nuclear clock. The required laser radiation at 148 nm wavelength has so far been produced using pulsed laser systems where only a small fraction of the incident photons has been resonant with the narrow nuclear transition. Here we show that the nuclear resonance can be excited with a continuous-wave narrow-bandwidth laser source with a power of less than 1 nW, and that the resonance signal can be detected in absorption rather than in fluorescence. This eliminates the slow nuclear fluorescence decay from the detection process and offers a considerable advantage for clock operation through fast signal acquisition. The VUV laser source is based on three sequential frequency doublings, starting from a diode laser at 1187 nm that is well suited for linewidth narrowing and for frequency comparisons with optical atomic clocks. We use absorption spectroscopy for the quantitative characterization of two different Th-centers in calcium fluoride crystal and measure the isomeric shift between them. One of the centers shows a very small static electric crystal field gradient 0.1 V/ $Å^2$ , to be compared to gradients in the range of 100 V/ $Å^2$ observed earlier. This indicates a center with high symmetry of the ions surrounding the Th nucleus, promising nuclear resonance lines that are nearly independent of the lattice spacing.A low-energy nuclear transition in the isotope thorium-229 has been excited in thorium-doped crystals with laser light. This opens the perspective towards a highly stable and robust solid-state optical nuclear clock. The required laser radiation at 148 nm wavelength has so far been produced using pulsed laser systems where only a small fraction of the incident photons has been resonant with the narrow nuclear transition. Here we show that the nuclear resonance can be excited with a continuous-wave narrow-bandwidth laser source with a power of less than 1 nW, and that the resonance signal can be detected in absorption rather than in fluorescence. This eliminates the slow nuclear fluorescence decay from the detection process and offers a considerable advantage for clock operation through fast signal acquisition. The VUV laser source is based on three sequential frequency doublings, starting from a diode laser at 1187 nm that is well suited for linewidth narrowing and for frequency comparisons with optical atomic clocks. We use absorption spectroscopy for the quantitative characterization of two different Th-centers in calcium fluoride crystal and measure the isomeric shift between them. One of the centers shows a very small static electric crystal field gradient 0.1 V/$Å^2$, to be compared to gradients in the range of 100 V/$Å^2$ observed earlier. This indicates a center with high symmetry of the ions surrounding the Th nucleus, promising nuclear resonance lines that are nearly independent of the lattice spacing.

physics.atom-phCross-listedarXiv:2604.16640Apr 21, 2026

Quantum-Mechanical Effects in Stimulated Optical Emission. II

Roscoe C. Williams

The existence of multiple-quantum transitions in optically pumped lasers, along with splitting of the laser line due to the modulation of the wave function at an angular frequency determined by the rate of pumping, is demonstrated for a certain class of incoherent broad-band sources pumping large pump bands in crystals. The source consists of a large number of stationary elements emitting wave fields continuously at various arbitrary frequencies and arbitrary phases. The distribution of frequencies and phases among the various elements is random. The pump band belongs to the class found in laser crystals of the ionic type. The analysis shows that such sources pumping such bands act like narrow-line sources pumping narrow lines. The effective linewidth is directly related to the pump rate.The existence of multiple-quantum transitions in optically pumped lasers, along with splitting of the laser line due to the modulation of the wave function at an angular frequency determined by the rate of pumping, is demonstrated for a certain class of incoherent broad-band sources pumping large pump bands in crystals. The source consists of a large number of stationary elements emitting wave fields continuously at various arbitrary frequencies and arbitrary phases. The distribution of frequencies and phases among the various elements is random. The pump band belongs to the class found in laser crystals of the ionic type. The analysis shows that such sources pumping such bands act like narrow-line sources pumping narrow lines. The effective linewidth is directly related to the pump rate.

Physical ReviewNov 2, 19641 citation

Å^2

, to be compared to gradients in the range of 100 V/

Å^2

observed earlier. This indicates a center with high symmetry of the ions surrounding the Th nucleus, promising nuclear resonance lines that are nearly independent of the lattice spacing.