Laser Frequency Shift Research Articles

Radiation reaction kinetics and collective QED signatures

Observing collective effects originating from the interplay between quantum electrodynamics and plasma physics might be achieved in upcoming experiments. In particular, the generation of electron–positron pairs and the observation of their collective dynamics could be simultaneously achieved in a collision between an intense laser and a highly relativistic electron beam through a laser frequency shift driven by an increase in the plasma density increase. In this collision, the radiation of high-energy photons will serve a dual purpose: first, in seeding the cascade of pair generation; and, second, in decelerating the created pairs for detection. The deceleration results in a detectable shift in the plasma frequency. This deceleration was previously studied considering only a small sample of individual pair particles. However, the highly stochastic nature of the quantum radiation reaction in the strong-field regime limits the descriptive power of the average behavior to the dynamics of pair particles. Here, we examine the full kinetic evolution of generated pairs in order to more accurately model the relativistically adjusted plasma density. As we show, the most effective pair energy for creating observable signatures occurs at a local minimum, obtained at finite laser field strength due to the trade-off between pair deceleration and the relativistic particle oscillation at increasing laser intensity. For a small number of laser cycles, the quantum radiation reaction may re-arrange the generated pairs into anisotropic distributions in momentum space, although, in the one-dimensional simulations considered here, this anisotropy quickly decreases.

Laser Frequency Shift and Stabilization of Atomic Fountain Based on Electro-Optic Modulation

Laser Frequency Shift and Stabilization of Atomic Fountain Based on Electro-Optic Modulation

Doppler effect of polarization grating.

The Doppler effect of motional polarization grating is studied for the first time to the best of our knowledge. Based on the optical properties of polarization grating, the Doppler effect principle of polarization grating is elucidated theoretically. A method to obtain the Doppler frequency shift based on beat frequency signal that is produced by superposition of order ±1 diffraction beams of polarization grating is proposed, and a proof-of-concept experiment is conducted to measure the frequency signal of the motional polarization grating. The movement characteristics of polarization grating varying with time can be obtained after a short-time Fourier transformation of the light signal. The experimental results are in good agreement with the theoretical predication, which verifies the correctness of the theoretical analysis and achieves the measurement of linear motion velocity and acceleration of motional polarization grating with high accuracy. This study proposes a new idea for laser frequency shift and has potential significance for further development of optical heterodyne detection.

Resonant four-photon scattering of collinear laser pulses in plasma.

Exact four-photon resonance of collinear planar laser pulses is known to be prohibited by the classical dispersion law of electromagnetic waves in plasma. We show here that the renormalization produced by an arbitrarily small relativistic electron nonlinearity removes this prohibition. The laser frequency shifts in collinear resonant four-photon scattering increase with laser intensities. For laser pulses of frequencies much greater than the electron plasma frequency, the shifts can also be much greater than the plasma frequency and even nearly double the input laser frequency at still small relativistic electron nonlinearities. This may enable broad range tunable lasers of very high frequencies and powers. Since the four-photon scattering does not rely on the Langmuir wave, which is very sensitive to plasma homogeneity, such lasers would also be able to operate at much larger plasma inhomogeneities than lasers based on stimulated Raman scattering in plasma.

Solid-state laser intra-cavity photothermal gas sensor

Compact, rugged and sensitive laser-based trace gas sensors are in high demand for science and commercial applications. To ensure high sensitivities, laser spectroscopic sensors often use extended interaction paths (e.g. multi-pass cells), which significantly increases their size, weight and susceptibility to misalignment. Herein, we present a novel, miniaturized photothermal gas sensor, where the gas sample is measured inside the resonator of a monolithic microchip solid-state laser operating at 1064 nm. The photothermal-induced gas refractive index variations are directly translated to a solid-state laser frequency shift, which is detected as a beatnote modulation in a heterodyne detection scheme. The system provides high sensitivity to refractive index changes at the level of ∼1.1 × 10−12 within ultra-short intra-cavity interaction path-length of 1.5 mm, which enables trace-gas measurements in a sensing volume of only 4 μl. In a proof-of-concept experiment using dry carbon dioxide as a test sample the sensor reached a minimum detection limit of 350 ppbv for a 100 s averaging time and NNEA = 4.1 × 10−8 [W cm−1 Hz−1/2].

Theoretical simulation of quantum cascade lasers based on InGaAs/AlInAs and InGaAs/AlAsSb quantum wells

Quantum cascade lasers based on semiconductor InGaAs/AlInAs and InGaAs/AlAsSb quantum wells exhibit electronic intersubband transitions within conduction bands and attract much attention due to their operation at room-temperature short wavelengths. In this work we performed a theoretical simulation of such quantum cascade lasers and studied the influence of their construction and application conditions on optical behaviour. The intersubband absorption processes in these quanta well structures were studied. Electronic properties and the conduction band edge profiles were simulated as well as the probability densities of the Wannier-Stark states were determined. The simulation results showed that with the rise of the temperature the threshold current density increases which also leads to a decrease in the optical gain. An increase of the applied electric field is accompanied by the optical gain rising and decrease of the threshold current density that results in a blue shift of laser frequency.

Laser frequency shift up to 5 GHz with a high-efficiency 12-pass 350-MHz acousto-optic modulator.

We demonstrate a novel laser frequency shift scheme using a 12-pass 350-MHz acousto-optic modulator (AOM). This AOM system shows better performance compared to ordinary acousto-optic modulation schemes. The frequency of the incident laser beam is shifted by 4.2 GHz with the total diffraction efficiency as high as 11%, and the maximum frequency shift is 5 GHz. Combining the ±1st order diffraction, laser signals with up to 10 GHz frequency difference can be obtained, which fulfill most frequency shift requirements of laser cooling and coherent manipulation experiments with alkali metal atoms.

Error analysis for lidar retrievals of atmospheric species from absorption spectra.

We generalize a model for retrieving atmospheric constituents from lidar absorption spectra measured at any laser frequency channels. Random and systematic retrieval errors from measurement noise and model bias, respectively, are analyzed parametrically and numerically to provide deeper insight. By placing four or more channels symmetrically around the absorption peak, retrieval errors from a common laser frequency shift and spectral baseline tilt can be eliminated. By solving for the frequency shift and spectral baseline tilt, atmospheric retrievals degrade only slightly even when such channels are shifted substantially out of symmetry. An etalon can thus be used for the wavelength stabilization.

Tailorable dispersion in a four-wave mixing laser.

We present experimental results demonstrating controllable dispersion in a ring laser by monitoring the lasing-frequency response to cavity-length variations. Pumping on an N-type level configuration in Rb87, we tailor the intra-cavity dispersion slope by varying experimental parameters, such as pump-laser frequency, atomic density, and pump power. As a result, we can tune the pulling factor, i.e., the ratio of the laser frequency shift to the empty cavity frequency shift, of our laser by more than an order of magnitude.

Note: A four-pass acousto-optic modulator system for laser cooling of sodium atoms.

We present a four-pass acousto-optic modulator (AOM) system for providing the repumping light for laser cooling of sodium atoms. With only one 400 MHz AOM, we achieve a tunable laser frequency shift around 1.6 GHz with total efficiency up to 30%. This setup provides an alternative over conventional methods to generate a sodium repumping light using more expensive high frequency AOMs or electro-optical modulators (EOMs) in the GHz domain. This compact and reliable setup can be easily adapted to other frequencies and may find applications in laser spectroscopy, laser cooling and trapping, and coherent manipulation of atomic quantum states.

引力波探测原理札记：LIGO干涉相移的五个起源

巨型迈克尔逊激光干涉仪是探测引力波的有效手段。本文研究了激光干涉引力波观察仪(Laser Interferometer Gravitational-Wave Observatory, LIGO)中的干涉臂长、干涉激光波长和频率等物理量在引力波振幅与引力波潮汐力作用下的变化量。本文总结出引力波引起LIGO干涉相位移动的五个物理因素: ①干涉臂标准长度的纯几何改变(非潮汐力贡献); ②激光标准波长的纯几何改变(非潮汐力贡献)；③干涉臂长度受潮汐力影响导致的改变(属引力波潮汐力贡献)；④激光波长受潮汐力影响导致的胀缩效应(属引力波潮汐力贡献)；⑤激光频率的弱相干效应。在引力波作用下，在互相垂直的两条干涉臂中的激光会有不同频移，这一频率弱相干条件也会影响干涉相位差。本文说明引力波潮汐力(引力落差)所导致的干涉激光波长屈伸效应能在LISA (Laser Interferometer Space Antenna)中有测量意义。本文还讨论了GW150914引力波信号频率变化率与描述螺旋合并双黑洞的引力波Blanchet频率方程之间的符合程度,发现GW150914引力波信号观察与理论在±30%差距上相符。 Giant Michelson interferometer is one of the essential means of gravitational wave detection. The influence of gravitational-tidal-force assisted laser wavelength stretch and laser-frequency soft coherence on the interference phase in LIGO (Laser Interferometer Gravitational-Wave Observatory) is investigated. It can be found that there are five physical origins of LIGO interference phase shift in LIGO gravitational wave detection: i) purely geometric change in standard length of interferometer arms (non-tidal contribution), ii) purely geometric change in standard length of laser wavelength (non-tidal contribution), iii) gravitational-wave tidal-force assisted change in interferometer arms (tidal contribution), iv) gravitational-wave tidal-force assisted change in laser wavelength (tidal contribution), and v) feeble coherence of laser frequency caused by gravitational wave in LIGO interferometer. The laser frequency shift in two vertical interference arms can occur due to gravitational wave, and hence such a faint coherence condition would also lead to interference pattern change when the gravitational wave propagates through the LIGO. The effect of flexion and extension in laser wavelength resulting from gravitational tidal force caused by a passing gravitational wave would have significance of measurement in LISA (Laser Interferometer Space Antenna). The frequency change rate of GW150914 gravitational wave signal resulting from in spiral, merger and ring-down of black-hole binaries has been addressed, and it can be found that the logarithm of the detected gravitational-wave frequency change rate agrees with the first-order Blanchet frequency equation within accuracy of ±30%.

Signal penalties induced by different types of optical filters in 100 Gbps PM-DQPSK based optical networks

Optical filters are crucial elements in optical communication networks. However, they seriously affect the signal quality, especially in the concatenation condition. In this paper, we study and simulate the signal penalties induced by five types of filters, including Butterworth, Gaussian, Bessel, Fiber Bragg Grating (FBG) and Fabry–Perot (F–P) filters, in order to optimize the optical network performance. Signal penalties, including both filter concatenation effect and filter induced in-band and out-band crosstalk, are analyzed by eye opening penalty (EOP) and Q-penalty. Simulation results show that the Butterworth filter performs best among these four types of filters. Total Q-penalty induced by a Butterworth filter-based demultiplexer/multiplexer pair, considering both filter concatenation effect and crosstalk, is lower than 0.5dB, when the filter bandwidth is in the range of 42–46GHz. Simulations done in a 100Gbps PM-DQPSK optical network indicate that the permitted cascaded number is 14 and 10 with respect to the case of filters aligned and misaligned, respectively. Penalties induced by laser frequency shift are investigated and the performance of the 3rd-order Butterworth filter is compared to the 4th-order superGaussian filter. Finally, discussions of optical filter performances, including insertion loss, reconfigurability and programmability, are presented.

A superradiant clock laser on a magic wavelength optical lattice.

An ideal superradiant laser on an optical clock transition of noninteracting cold atoms is predicted to exhibit an extreme frequency stability and accuracy far below mHz-linewidth. In any concrete setup sufficiently many atoms have to be confined and pumped within a finite cavity mode volume. Using a magic wavelength lattice minimizes light shifts and allows for almost uniform coupling to the cavity mode. Nevertheless, the atoms are subject to dipole-dipole interaction and collective spontaneous decay which compromises the ultimate frequency stability. In the high density limit the Dicke superradiant linewidth enhancement will broaden the laser line and nearest neighbor couplings will induce shifts and fluctuations of the laser frequency. We estimate the magnitude and scaling of these effects by direct numerical simulations of few atom systems for different geometries and densities. For Strontium in a regularly filled magic wavelength configuration atomic interactions induce small laser frequency shifts only and collective spontaneous emission weakly broadens the laser. These interactions generally enhance the laser sensitivity to cavity length fluctuations but for optimally chosen operating conditions can lead to an improved synchronization of the atomic dipoles.

Design of High Stability of DDS Signal Source for Laser Frequency Shift

Acousto-optical-Modulator (AOM)'S characteristics of shift frequency can be used to change the frequency of laser, the performance of AOM will improve directly by a high stability driving signal source. The paper presents a design of high stability of DDS signal source for laser frequency shift, the signal source output frequency range of 50MHz-400MHz. Using atomic frequency standard and external frequency multiplier as the reference source of DDS to make its frequency stability reaches , using sub-octave filter to get a high output signal spectral purity.

多光束傅里叶望远镜的移频设计

多光束傅里叶望远镜的移频设计

High-speed acousto-optic shutter with no optical frequency shift

Acousto-optic modulators are widely used for rapid switching and shuttering of laser beams. In many applications, the concomitant frequency shift is undesirable and must be compensated for elsewhere in the system. Here we present a simple method of achieving rapid laser power switching without an accompanying laser frequency shift. The demonstrated acousto-optic shutter achieves a switching time of around 25 ns, an extinction ratio of 46 dB, and efficiency comparable to a conventional double-pass acousto-optical modulator configuration.

Frequency stabilization of pulsed CO2 laser using setup-time method

A new method for laser-frequency stabilization by controlling the pulse setup time is presented. The frequency-stabilization system monitors the pulse setup time continuously, and controls it by adjusting the cavity length. Laser frequency is stabilized to the center of the gain curve when the setup time is the shortest. The system is used to stabilize a radio-frequency-excited waveguide CO2 laser tuned by grating, and the shift of laser frequency is estimated to be less than §25 MHz for an extended period. The system has the advantages of compact structure, small volume, and low cost. It can be applied for frequency stabilization of other kinds of pulsed lasers with adjustable cavity.

傅里叶望远镜中激光频移误差对成像质量影响的分析

傅里叶望远镜中激光频移误差对成像质量影响的分析

激光二极管自混合干涉和激光的频移

激光二极管自混合干涉和激光的频移

Calculation of the optimal polarisation anisotropy of interference mirrors of a ring laser resonator

The influence of the amplitude—phase polarisation anisotropy of the interference mirrors on the polarisation characteristics of a ring laser (ellipticity, frequency shifts, and losses) is analysed. The combination of the mirror parameters, at which the maximum sensitivity of the polarisation characteristics of radiation to the nonplanar deformation of the axial contour is observed, is determined. It is shown that there exists a range of optimal phase anisotropies of the mirrors.