Faraday Anomalous Dispersion Optical Filter Research Articles

Switchable Faraday laser with frequencies of 85Rb and 87Rb 780 nm transitions using a single isotope 87Rb Faraday atomic filter

In the development of atomic physics, laser sources with Frequencies corresponding to atomic transition and high stability are essential. The Faraday laser is a special diode laser using the Faraday anomalous dispersion optical filter (FADOF) to realize frequency selection, so the output laser frequency is automatically limited to the atomic Doppler broadening. However, the frequency of a Faraday laser corresponds to the range around only one atomic hyperfine transition. Here, we realize a switchable Faraday laser with two isotopes laser frequencies corresponding to 85Rb 52S1/2 (F=3)→52P3/2 and 87Rb 52S1/2 (F=2)→52P3/2 transitions based on a single isotope 87Rb-FADOF. The laser has good robustness against the fluctuation of diode current and temperature, with wavelength fluctuating within 0.8 pm from 16 to 30 °C of diode temperature, and has a free-running linewidth of 18 kHz. We also lock the laser frequency to the two cycling transitions of 85Rb 52S1/2 (F=3)→52P3/2 (F′=4) and 87Rb 52S1/2 (F=2)→52P3/2 (F′=3) by the modulation transfer spectroscopy technique. The Allan deviation of the residual error signal is 3×10−14/τ, and the frequency stability of the beat detection reaches 2.8×10−12 at 1 s integration time. This 780 nm switchable Faraday laser expands the application scenarios of Faraday lasers, which can be used in laser cooling atoms, optical frequency standards, and other quantum precision measurement fields.

Ghost imaging under direct sunlight conditions using FADOF

Sunlight background noise significantly hinders the operation of ghost imaging systems, posing a considerable challenge for target imaging under daytime sunlight conditions. This paper introduces a method to eliminate sunlight background noise using a Faraday anomalous dispersion optical filter (FADOF). A ghost imaging system based on FADOF is constructed, and experiments are conducted under strong background noise conditions. The system operates outdoors in direct sunlight, utilizing sunlight introduction system to introduce light into the detection path, directly reaching the detection end of the system. In this real sunlight noise condition, the ghost imaging system using FADOF filtering achieved nearly continuous and stable imaging throughout three summer days, contrasting with a system using a 10 nm filter that only functions properly after sunset. The research findings indicate that FADOF effectively enhances the ghost imaging system's resistance to background light noise, enabling continuous operation under conditions of strong background noise throughout the day.

Design of a Data Acquisition, Correction and Retrieval of Na Doppler Lidar for Diurnal Measurement of Temperature and Wind in the Mesosphere and Lower Thermosphere Region

Based on the resonance fluorescence scattering mechanism, a narrowband sodium (Na) lidar can measure temperature and wind in the mesosphere and lower thermosphere (MLT) region. By using a narrowband spectral filter, background light noise during the day can be suppressed, allowing for continuous observations. To obtain full-diurnal-cycle temperature and wind measurement results, a complex and precise retrieval process is required, along with necessary corrections to minimize measurement errors. This paper introduces the design of a data acquisition unit for three frequencies in three directions of the Na lidar system in the Chinese Meridian Project (Phase II) and investigates the calibration and retrieval methods for obtaining diurnal temperature and horizontal wind in the MLT region, using a Na Doppler lidar with Faraday anomalous dispersion optical filter (FADOF). Furthermore, these methods are applied to observations conducted by a Na lidar in Beijing, China. The wind and temperature results over full diurnal cycles obtained from the all-solid-state Na Doppler lidar are reported for the first time and compared with temperature measurements from satellite, as well as wind observations from a meteor radar. The comparison demonstrates a reasonable agreement between the results, indicating the rationality of the lidar-retrieved results and the feasibility and effectiveness of the data correction and retrieval method.

Research on Solid-state Optical Filtering Technology Using Faraday Anomalous Dispersion in Rare Earth-doped Crystals

This paper proposes a Faraday anomalous dispersion optical filter that uses rare earth-doped crystals to overcome the limitations of current atomic filtering technology, which include limited working wavelength and Doppler broadening. The paper analyses Er3+: LiYF4 1530 nm as an example filter. The results show that the proposed filter achieves high transmission while maintaining an ultra-narrow bandwidth transmission spectrum. The maximum transmission efficiency reaches 94.8% with a transmission bandwidth of hundred trillions HZ. The position of the transmission peak can be tuned by adjusting the size of the magnetic field, enabling the conversion of the transmission spectrum between the line center and the line wing.

Cold-atom optical filtering enhanced by optical pumping

Atomic optical filters such as Faraday anomalous dispersion optical filters (FADOFs) or similar technologies can achieve very narrow optical bandwidth close to the scale of atomic linewidth, which can be greatly reduced in cold atoms. However, limited by the number of cold atoms and the size of the cold atomic cloud, the number of atoms interacting with the laser is reduced, and the transmission remains as low as 2%. In this work, we introduce the optical pumping into the cold atomic optical filter to solve this problem. Circular polarized optical pumping can produce polarization of the atomic ensemble and induce dichromatic as well as the Faraday rotation. We demonstrate a cold-atom optical filter which operates on the 87Rb 52S1/2 (F=2) to 52P3/2 (F′=2) transition at 780 nm. The filter achieves an ultranarrow bandwidth of 6.6(4) MHz, and its peak transmission is 15.6%, which is nearly 14 times higher than that of the cold-atom optical filter realized by Faraday magneto-optic effect. This scheme can be extended to almost all kinds of atomic optical filters and may find applications in self-stabilizing laser and active optical clock.

Using FADOF to eliminate the background light influence in ghost imaging.

The high solar background during the day adversely affects the long distance daytime operations of ghost imaging. It is extremely hard to distinguish the signal light from the background noise light after they are both converted to voltage or current signals by the bucket detector, so spectral filtering before the detector is quite important. In this work, a Faraday anomalous dispersion optical filter (FADOF) is used in eliminating the background light influence in ghost imaging. Results of lab experiment show that the background light noise tolerance of the ghost imaging with FADOF is at least 18 times bigger than that with a 10 nm optical filter. The method has simple structure, great performance and great algorithms compatibility.

Polarization insensitive efficient ultra-narrow diode laser strictly locked by a Faraday filter.

A Faraday anomalous dispersion optical filter (FADOF) could lock high-power diode lasers to atomic resonance lines with ultra-narrow bandwidth. However, the polarization sensitivity of the Faraday filter limits its applications since the standard diode module often employs polarization combination to increase pumping brightness. We proposed a polarization-insensitive mutual injection configuration to solve this problem and locked a standard polarization combined diode module to Rb D2-line. The laser bandwidth was narrowed from 4 nm to 0.005 nm (2.6 GHz, FWHM) with 38.3 W output and an external cavity efficiency of 80%. This FADOF-based polarization-insensitive external-cavity scheme would find many applications, such as high energy atomic gas laser pumping (alkali lasers, metastable rare gas lasers) and quantum optics, etc.

A dual-wavelength bandpass Faraday anomalous dispersion optical filter operating on the D1 and D2 lines of rubidium

A dual-wavelength bandpass Faraday anomalous dispersion optical filter (DW-FADOF) operating at both the D1 and D2 lines of rubidium is experimentally demonstrated. The effects of certain system parameters, such as the incident laser power, magnetic field strength, and atomic density, on the performance of the filter are experimentally and theoretically investigated. Through elaborate simulation, an appropriate set of system parameters is selected, and the DW-FADOF achieves peak transmittance of 37.4% with a figure of merit (FOM) of 0.10 GHz−1 in the D1 line and 77.9% with a FOM of 0.33 GHz−1 in the D2 line, simultaneously. This FADOF provides transmission bands covering both two typical atomic transitions, and it can be used as a dual signal carrier. Due to the integration and minimization of loss, the results confirm the significant application potential of this filter in wavelength division multiplex communication and weak signal extraction.

18W ultra-narrow diode laser absolutely locked to the Rb D2 line.

We described a wavelength locked and spectral narrowed high-power diode laser with a Faraday anomalous dispersion optical filter (FADOF). By an external cavity with a 85Rb FADOF, the central wavelength of the diode laser was precisely locked to the Rb resonance D2 line. The bandwidth was narrowed from the free-running 4 nm to 0.002 nm (1.2 GHz, FWHM). At 4.9 A maximal driven current, the laser produced a continuous wave (CW) output of 18 W with an external cavity efficiency of 80%, either the current or the temperature had no impact on the central wavelength of the diode laser. The Rb cell works well without any damage under a long-time running. This ultra-stable and extreme-narrowed high power diode laser would find many applications in alkali lasers pumping, metastable rare gas laser pumping, spin-exchange optical pumping, and quantum optics.

Thermal and temporal characteristics of Faraday anomalous dispersion optical filters based on a hollow cathode lamp.

As a new, to the best of our knowledge, alternative to the saturated vapor-cell-based Faraday anomalous dispersion optical filter (FADOF), the FADOF based on a hollow cathode lamp (HCL-FADOF) not only enables the FADOF to work normally at room temperature without heating, but also has some new features due to the inherent characteristics of the HCL. In this Letter, we implement an HCL-FADOF operating on the rubidium D2 line and experimentally investigate the effect of ambient temperature on its performance and cold-start characteristics. Results show that the HCL-FADOF can provide excellent stability within a large temperature range, even at temperatures below 0°C. A comparison of the start performance between the HCL-FADOF and FADOF using saturated vapor cells is also provided. This work shows unique features of the HCL-FADOF in a low-temperature environment and its quick-start advantage, which provides a solid foundation for extensive applications.

Demonstration of Faraday anomalous dispersion optical filter with reflection configuration

A narrow linewidth Faraday anomalous dispersion optical filter (FADOF) with reflection configuration is achieved for the first time based on the cesium (Cs) ground state 6S1/2 to the excited state 6P3/2 transition at 852 nm. Compared with the conventional FADOF with transmission configuration, reflection-type FADOF can greatly improve the transmittance of optical filter under the same experimental parameters, because it allows signal light to go and return through the atomic vapor cell. In our experiment, peak transmittance at Cs 6S1/2 F = 4–6P3/2 transition is 81% for the reflection-type FADOF, and while 54% for the transmission-type FADOF when the temperature of Cs vapor cell and the axial magnetic field are 60 °C and 19 G. The idea of this reflection-type FADOF design has the potential to be applied to the FADOF operating between two excited states to obtain higher transmittance.

A Faraday Anomalous Dispersion Optical Filter Based on Rubidium Hollow-Cathode Lamp

Using a hollow-cathode lamp (HCL) to build a Faraday anomalous dispersion optical filter (FADOF) is a new method to realize narrow linewidth optical filters. In contrast to other atomic optical filters based on saturated vapors, which work at a relatively high temperature to maintain the atomic density, the HCL device using sputtered particles can work at a much lower temperature. In this work, a rubidium HCL-based FADOF (HCL-FADOF) working at 780 nm is established and carefully tested. With 20 mm cathode length, the transmittance can reach 29% under 18 mA discharge current and 260 G magnetic field at room temperature, which is equivalent to the performance of a saturated vapor-based FADOF (VC-FADOF) at more than 60 ∘C. This work provides a direct comparison of the performance of the HCL-FADOF and the VC-FADOF, which is of great benefit to further studies of atomic filters at normal temperature.

A Dual-Frequency Faraday Laser

The Faraday laser, with Faraday anomalous dispersion optical filter (FADOF) as frequency-selection element, is a natural narrow-bandwidth light source for laser physic experiments. In this work, a dual-frequency (DF) Faraday laser is demonstrated for the first time on Cs D2 line at 852 nm. The frequencies of the two modes of DF Faraday laser hinge on the peak transition frequencies of 852 nm FADOF transmittance spectrum corresponding to the ground state F=4 and F=3. The frequency difference between the two modes is tunable over a range of 1.4 GHz with the temperature of Cs vapor cell inside the FADOF. The linewidth of each laser mode is less than 33 kHz. Furthermore, the most probable linewidth of the beat-note spectra between the two modes is 902.95 Hz at different vapor-cell temperatures. Such a DF Faraday laser has many potential applications in atomic physics, such as sub-Doppler spectroscopy and coherent population trapping atomic clocks.

Isotope 87Rb Faraday filter with a single transmission peak resonant with atomic transition at 780 nm.

We demonstrate an isotope 87Rb Faraday anomalous dispersion optical filter (FADOF) with a single transmission peak resonant with the 5S1/2, F = 2 → 5P3/2, F' = 1, 2, 3 transitions at 780 nm with an enriched 87Rb isotope at low temperature. The isotope 87Rb FADOF achieves a single peak transmission of 74.8% with a bandwidth of 0.96 GHz. Compared with most of FADOFs operated at frequencies far from absorption, the isotope 87Rb FADOF that we have achieved can provide a transmission band exactly covering atomic transitions for many practical applications.

Induced-Dichroism-Excited Atomic Line Filter at 1529 nm

An induced-dichroism-excited atomic line (IDEAL) filter at 1529 nm operating on the transition of 87 Rb 5 2 P3/2-4 2 D3/2 is realized. Its peak transmittance achieves 63.8% at 80 °C by a 13.4 mW/mm 2 laser pumping at 780 nm and the equivalent noise bandwidth is 546 MHz. Detailed experiments show that, compared with the excited-state Faraday anomalous dispersion optical filter and excited-state Voigt atomic line filters which are realized by the same atomic vapor cell, operating on the same transition and under the same pumping intensity, the IDEAL filter achieves the same performance level without the magnetic field. This letter provides a new solution to ultra-narrow optical filtering at 1529 nm, and it is particularly useful in applications which require non-magnetic environments.

Signal intensity influences on the atomic Faraday filter.

Previous studies of the Faraday anomalous dispersion optical filter (FADOF) mainly focus on the weak signal light filtering, without regard for the influences of the signal light intensity on the filter itself. However, in some applications the signal light is strong enough to change the filter's performance. In this work, the influences of the signal light intensity on the transmittance spectrum is experimentally investigated in a 780nm Rb85 FADOF in both the line-center and wings operation modes. The results show that the transmittance spectrum varies significantly with the signal light intensity. As the signal light increases, some existing transmittance peaks decline, some new transmittance peaks appear, and the maximum transmittance peak frequency may change. The spectrum in strong signal lights can be quite different from those calculated by programs in the condition of weak signal lights. These results are important for applications of the FADOF in the condition of strong signal lights.

Atomic optical stimulated amplifier with optical filtering of ultra-narrow bandwidth

Taking advantages of ultra-narrow bandwidth and high noise rejection performance of the Faraday anomalous dispersion optical filter (FADOF), simultaneously with the coherent amplification of atomic stimulated emission, we propose a stimulated amplified Faraday anomalous dispersion optical filter (SAFADOF) at cesium 1470 nm. The SAFADOF is able to significantly amplify very weak laser signals and reject noise in order to obtain clean signals in strong background. We show that for a weak signal of 50 pW, the gain factor can be larger than 25000 (44 dB) within a bandwidth as narrow as 13 MHz. Having the ability to amplify weak signals with low background contribution, the SAFADOF finds outstanding potential applications in weak signal detections.

The Characteristics of Ar and Cs Mixed Faraday Optical Filter Under Different Signal Powers

The characteristics of the 852 nm cesium Faraday anomalous dispersion optical filter with Ar-filled cesium cell under different signal powers are investigated. The transmittance spectra are measured by changing the input laser power from 0.05 to 10 mW (the irradiance from 12.03 to 2406.88 W/m2) and the buffer gas pressure from 1 to 10 torr. The spectra without the buffer gas are also measured. The results reveal the entirely different variations of the transmittance spectra for the cells with and without the buffer gas. For the cell without the buffer gas, the sidebands of the spectrum get higher and the bandwidth is broadened as the input power increases. However, for the cell with the buffer gas, the sidebands are suppressed and the bandwidth is reduced. A single-peak transmittance spectrum will be formed eventually. These phenomena are remarkable at relatively high pressures of Ar (5 and 10 torr), which may be very suitable for applications such as Faraday laser, optical frequency standard, laser frequency stabilization, and laser locking. The sidebands of the spectrum can also be used to restrict the high input laser power which may cause damage to the system.

Intensity correlation imaging with sunlight-like source

We show a method of intensity correlation imaging of targets illuminated by a sunlight-like source both theoretically and experimentally. With a Faraday anomalous dispersion optical filter (FADOF), we have modulated the coherence time of a thermal source up to 0.167 ns. And we carried out measurements of temporal and spatial correlations, respectively, with an intensity interferometer setup. By skillfully using the even Fourier fitting on the very sparse sampling data, the images of targets are successfully reconstructed from the low signal-noise-ratio(SNR) interference pattern by applying an iterative phase retrieval algorithm. The resulting imaging quality is as well as the one obtained by the theoretical fitting. The realization of such a case will bring this technique closer to geostationary satellite imaging illuminated by sunlight.

A Faraday laser lasing on Rb 1529\u2009nm transition

We present the design and performance characterization of a Faraday laser directly lasing on the Rb 1529 nm transition (Rb, 5P3/2 − 4D5/2) with high stability, narrow spectral linewidth and low cost. This system does not need an additional frequency-stabilized pump laser as a prerequisite to preparing Rb atom from 5S to 5P excited state. Just by using a performance-improved electrodeless discharge lamp-based excited-state Faraday anomalous dispersion optical filter (LESFADOF), we realized a heterogeneously Faraday laser with the frequency corresponding to atomic transition, working stably over a range of laser diode (LD) current from 85 mA to 171 mA and the LD temperature from 11 °C to 32 °C, as well as the 24-hour long-term frequency fluctuation range of no more than 600 MHz. Both the laser linewidth and relative intensity noisy (RIN) are measured. The Faraday laser lasing on Rb 1529 nm transition (telecom C-band) can be applied to further research on metrology, microwave photonics and optical communication systems. Besides, since the transitions correspongding to the populated excited-states of alkali atoms within lamp are extraordinarily rich, this scheme can increase the flexibility for choosing proper wavelengths for Faraday laser and greatly expand the coverage of wavelength corresponding to atomic transmission for laser frequency stabilization.