FM noise of index-guided GaAlAs diode lasers

The FM-noise spectrum of index-guided GaAlAs-diode lasers is measured for different lengths of the laser cavity. The observed FM-noise peak near the internal laser resonance and the decrease of the FM noise with increasing cavity length is in agreement with a model which is considering the spontaneous emission noise source. From the measured noise data, the linewidth enhancement factor is determined.     

Stability and noise properties of diode lasers with phase-conjugatefeedback

For a diode laser subjected to filtered feedback from a phase-conjugating mirror, we present the first exact stability analysis and various noise spectra. The stability properties are intermediate between those of the injection laser and the laser with conventional optical feedback. The role of a finite response-time is to drastically enhance the steady-state stability For moderate feedback, the frequency noise is suppressed by several orders of magnitude, and the main relaxation frequency of the laser shows a crossover from the usual relaxation oscillation frequency to a new frequency determined by the amount of feedback. This may be of technological importance since it is expected to improve the modulation bandwidth     

All-electronic suppression of mode hopping noise in diode lasers

A simple all-electronic stabilization scheme is presented for suppression of external-cavity mode-hopping noise in diode lasers. This excess noise is generated when the laser is subjected to optical feedback and may degrade the overall performance of optical systems including sensors. Suppression of the noise has been demonstrated to improve the sensitivity of a coherent sensor by more than 23 dB     

氦-镉激光器电离波频率噪声的研究

通过对氦-镉激光器激光噪声谱上不连续振荡噪声分量的测试,发现放电管的边界条件、放电电流和镉密度对电离波频率特征峰的功率、频率、调制度、1/f噪声范围和其余噪声均有影响。得到电离波频率特征峰处100％的调制度结果。     

Frequency noise measurement of diode-pumped Nd:YAG ring lasers

The combined frequency noise spectrum of two lightwave Model 120-01A nonplanar ring oscillator lasers was measured by first heterodyne detecting the IF signal and then measuring the IF frequency noise using an RF frequency discriminator. The results indicated the presence of a 1/f² noise component in the power spectral density of the frequency fluctuations between 1 Hz and 1 kHz. After incorporating this 1/f² into the analysis of the optical phase tracking loop, the measured phase error variance closely matches the theoretical predictions     

Limitations and noise in interferometric systems using frequency ramped single-mode diode lasers

Frequency ramped diode laser sensing and measurement systems suffer from a variety of limitations and noise sources. Nonlinearities in the frequency ramp produce unwanted sidebands in the frequency spectra of the system output and make accurate distance determination difficult in the frequency domain. Thermally induced drifts in the laser frequency prohibit long-term sensitive phase measurements even with a reference interferometer. It is shown that phase noise due to the fundamental linewidth of the diode laser and not bias current noise determines the noise floor of most FMCW systems in the regimes away from (1/f) noise. Time domain techniques suffer from low resolution because only a few data points can be taken during each frequency ramp and thus achieve poor averaging of the phase noise. The signal to noise ratio (SNR) of frequency ramped systems is shown to be lower (10-30 dB) than the theoretical prediction for an unmodulated heterodyne system, which was substantiated by showing that the minimum detectable phase is somewhat higher than that predicted by the idealized model.     

Coupled-mode analysis of a periodic array of diode lasers

A generalised eigenmode analysis of phased-array diode lasers is presented that takes account of modal overlap between adjacent channels. The effect of the overlap is to modify supermode gain splitting nonuniformly. Current spreading suppresses supermode discrimination, resulting in single-lobed far-field operation of arrays with closely spaced lasers.     

半导体抽运Nd:YAG激光器强度噪声抑制的研究

为了降低半导体抽运固体激光器的弛豫振荡噪声,提高其输出功率的稳定性,采用光电负反馈的方法来抑制半导体抽运的固体激光器的强度噪声,并对激光器强度噪声的理论特性进行了分析。根据理论分析结果设计了比例-积分-微分反馈控制电路,通过运用该反馈电路对激光器进行强度噪声抑制实验,得到了比较理想的实验数据,即当抽运功率为700mW、弛豫振荡峰频率为300kHz时,弛豫振荡峰值处和低频区域强度噪声分别降低了45dB和15dB;当抽运功率为550mW、弛豫振荡峰值为250kHz时,弛豫振荡峰值处和低频区域强度噪声分别降低了40dB和10dB。结果表明,该反馈控制电路能够有效地降低半导体抽运固体激光器的强度噪声,提高激光器输出功率的稳定性。     

Optical and electronic reduction of Rayleigh backscatter noise in fibre-coupled semiconductor diode lasers

Optical and electronic feedback techniques have been implemented to reduce the noise induced by Rayleigh backscatter in a semiconductor laser endfire-coupled to an optical fibre. An intensity noise reduction of 12 dB and a frequency noise reduction of 30 dB were observed.     

Line broadening and intensity noise due to polarization switchingin external cavity diode lasers

The authors report on polarization switching as a new source of linewidth broadening and intensity noise in external grating diode laser setups that emit in a sequence of alternating wavelength intervals having TE and TM polarization, respectively. At the borders between two consecutive intervals, the continuous random hopping of the system between the two polarizations results in line broadening and in RIN values of -100 dB/Hz at frequencies below 100 MHz. In the middle part of each wavelength interval, linewidth of less than 300 kHz and low noise (<-145 dB/Hz) have been measured     

双光子激光器中噪声效应的半经典分析

应用Lamb的半经典激光理论,分析了散粒噪声和热噪声对激光特性的影响.推导了在散粒噪声和热噪声存在时激光场几率分布的Fokker-Planck方程,得到了计及噪声时聚束和反聚束的判据.并与单光子激光中噪声存在时相应的结果进行了比较.     

Single-lobe phased-array diode lasers

We show mathematically that the lowest-order supermode of a real-refractive-index phase-locked semiconductor diode laser array, which radiates into a single narrow far-field lobe, is favoured by its lower threshold when the gain in the interspaces between the waveguides exceeds that of the waveguides themselves.     

Q-switched semiconductor diode lasers

Diode lasers with an intracavity electroabsorption modulator have been operated with full on/off modulation at rates of 3 GHz. In addition, modulation of the lasers has been shown up to a detector-limited frequency of 6 GHz. A new model of these devices, which includes amplified spontaneous emission and high gain is developed in this paper. A quasi-static gain approximation is introduced and the dynamics of the electron and photon population are modeled by three coupled nonlinear difference equations which can be numerically solved with very little computation time. The model predicts the possibility of a new mode ofQ-switched operation with the capacity for repetition rates of tens of gigahertz and binary pulse position modulation at rates of the order of 10 Gbits/s.     

New optically pumped far-infrared lasers

Ninety-seven new far-infrared (FIR) laser transitions have been observed in optically pumped ethylene glycol, dimethyl ether, formic acid, and monomethyl amine, all excited by a pulsed CO2laser.     

Injection locking of diode lasers

We present a theoretical analysis of the forward and reflected amplitudes in a diode laser oscillator cavity for both a single resonant mode and an injected signal. The analysis includes gain saturation and allows the gain coefficient at the injected frequency to be different from that at the resonant frequency. Analytic solutions for the axially dependent amplitudes are presented for the case of equal gain coefficients. For the more general case, a formula is presented for the intensity necessary for locking, which is shown to reduce in various limits to other expressions previously published. One immediate consequence of the present formalism is that the use of antireflection coatings on the diode end facets should act to reduce the injected signal intensity necessary for locking. In fact, reduction of the reflectivities to values of a few percent should enable locking over the entire gain curve with incident intensities which are small compared to the slave oscillator's normal output.     

Optimal design of optically side-pumped lasers

A ray-tracing algorithm is used to determine the pump-absorption distribution, and the mode-coupling efficiencies to specific transverse modes are calculated. We develop a model for optimizing the pumping geometry for an optical side-pumped laser medium. Analytic and numerical results are given for the case of TEM₀₀ laser output arising from a few examples of Gaussian pumping. We also model the performance of a close-coupled, side-pumped configuration that is found in numerous recent high-power laser-diode-pumped solid-state lasers. A particular advantage of this system approach is that it allows characterization and selection of pump configurations before fabrication of the pump cavity     

Theory of optically pumped submillimeter lasers

Theoretical models of the operating characteristics of both pulsed and CW optically pumped submillimeter (SMM) lasers are reviewed. The SMM laser gain is discussed for both pressure and Doppler broadened transitions. A review is given of expressions for SMM laser gain based on quantum mechanical calculations in a three-level molecular system.     

Stability of single-mode optically pumped lasers

We study mode competition in optically pumped lasers with one active laser line. The stability of single-mode operation under one mode pumping (both fields arbitrarily intense) is determined by calculating the saturated laser gain using either a mono- or bichromatic probe. The probe spectra differ dramatically from the single-mode, intense field gain curves occasionally exploited in this context in earlier works. Some features in the spectra are interpreted with the dressed atom picture. The mathematically simpler single probe gain is shown to be a good approximation for large mode spacings. When the strong field induced Rabi flipping is comparable to the mode spacing, however, a bichromatic probe containing two frequencies which are symmetric with respect to the intense mode is usually needed. Typical mono- and bichromatic probe spectra are discussed and parameter regions are explored which give stable single-mode operation. The results are also relevant in general laser instability studies: some aspects due to the strong field induced coherences will be pointed out.     

Frequency and intensity noise in injection-locked semiconductor lasers: Theory and experiments

Analytical expressions for the power spectral densities of intensity and frequency noise of single-mode semiconductor lasers operating in a regime of injection locking are derived by appropriately taking into account the spontaneous emission processes into the lasing modes of both the master and slave lasers. They show how the noise spectra of the slave are influenced by the value of the injected power, by the difference between the emission frequencies of the master and slave optical cavities, and how they are correlated to the noise properties of both the master and the free-running slave. In particular, the very low frequency part of the frequency noise of the slave turns out to coincide with that of the master within a certain frequency region whose range increases as the values of the injected signal does, too. We also present measurements of the power spectral densities obtained by means of an experimental apparatus similar to that described in [1] and show how the experimental results are accounted for by the present theory.