We have demonstrated a laser in which the frequency shift due to small cavity fluctuations is far less than what would be expected from a conventional laser. The factor of sensitivity suppression is inferred to be equal to the effective group index experienced by the laser, implying that this laser is subluminal. We have observed a suppression factor as high as 663. Such a laser is highly self-stabilized compared to a conventional laser, and is expected to have a far smaller Schawlow-Townes linewidth. As a result, this laser may have potentially significant applications in the fields of high-precision optical metrology and passive frequency stabilization.
Indium oxide-doped hematite xIn 2 O 3 * (1 − x)α-Fe 2 O 3 (molar concentration x = 0.1-0.7) solid solutions were synthesized using mechanochemical activation by ball milling. XRD patterns yield the dependence of lattice parameters and grain size as function of milling time. After 12 h of milling, the completion of In 3+ substitution of Fe 3+ in hematite lattice occurs for x = 0.1. For x = 0.3, 0.5 and 0.7, the substitutions between In 3+ and Fe 3+ into hematite and respectively, In 2 O 3 lattices occur simultaneously. The lattice parameters of α-Fe 2 O 3 (a and c) and In 2 O 3 (a) vary with milling time. For x = 0.1, Mössbauer spectra were fitted with one, two, or three sextets versus milling time, corresponding to gradual substitution of In 3+ for Fe 3+ in hematite lattice. For x = 0.3, Mössbauer spectra after milling were fitted with three sextets and two quadrupole-split doublets, representing In 3+ substitution of Fe 3+ in hematite lattice and Fe 3+ substitution of In 3+ in two different sites of In 2 O 3 lattice. For x = 0.5 and 0.7, Mössbauer spectra fitting required two sextets and one quadrupole-split doublet, representing coexistence of In 3+ substitution of Fe 3+ in hematite lattice and Fe 3+ substitution of In 3+ in indium oxide lattice. The recoilless fraction studied versus milling time for each molar concentration exhibited low values, consistent with the occurrence of nanoparticles in the system. SEM/EDS measurements revealed that the mechanochemical activation by ball milling produced xIn 2 O 3 * (1 − x)α-Fe 2 O 3 solid solution system with a wide range of particle size distribution, from nanometer to micrometer, but with a uniform distribution of Fe, In, and O elements.
In this paper, we report a Raman laser which is extremely sensitive to a variation of the cavity length, using a scheme employing two stable isotopes of Rb. One isotope is used for producing a broad gain spectrum via the optically pumped Raman gain process, while the other is used for producing a narrow dip via the optically pumped Raman depletion process. By tuning the frequencies of the two Raman pumps, the center frequencies of the gain and dip can be aligned to the same frequency. This approach allows tuning of the gain and dip parameters independently over a broad range of operating conditions. With such a configuration, we can produce a negative dispersion around the two-photon resonance frequency in the vapor cell, which leads to a group index that is close to zero. By theoretically matching the experimental observations, we can infer that the sensitivity of such laser is enhanced by a factor of more than 2800, which is nearly a factor of three larger than the highest value reported previously using a different approach.
In this paper, we present the experimental observation of simultaneous bi-directional superluminal lasing in a triangular ring cavity without gain competition and crosstalk as needed for realizing a gyroscope based on the Sagnac effect. The gain spectrum for each of the lasers is tailored to be a narrow dip on top of a broad gain using two stable isotopes of Rb. Specifically, we make use of 85Rb to produce a broad gain spectrum via the optically pumped Raman gain process and 87Rb to produce a narrow absorption spectrum via the optically pump Raman depletion process. A separate gain cell is used for the laser in each direction. Inferred from the simulation, the spectral sensitivity enhancements of the clock-wise and counter-clock-wise superluminal ring lasers are ∼362 and ∼505, respectively, with the imbalance attributed to differences in pump powers.
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