Laser Amplitude Noise Research Articles

Amplitude noise reduction of 50 dB in colliding-pulse mode-locking dye lasers

Spurious sidebands observed in the noise spectrum of colliding-pulse mode-locking dye lasers result from coupling of the longitudinal mode beating modulations of the (argon-ion) pump laser with the dye laser. We achieve a 50-dB amplitude noise reduction at the mixing frequencies by inserting a single-frequency étalon in the argon-laser cavity. Furthermore, we find the amplitude noise of the colliding-pulse mode-locking laser to be entirely dominated by the (plasma discharge) noise of the argon laser.

Reduction of semiconductor laser diode phase and amplitude noise in interferometric fiber optic sensors

An optical configuration employing two conventional Michelson interferometers and a fiber Fabry-Perot interferometer connected in parallel is used to demonstrate the principle of common mode rejection of both the amplitude and frequency noise of a semiconductor laser. Common mode noise rejection is maximized when the outputs of the two interferometers with matched path imbalance, fringe visibility and amplitude are differentially combined. One interferometer is used as a reference, and the other as a sensing interferometer. The fiber Fabry-Perot interferometer is used as the sensing interferometer and is demonstrated as a miniature acoustic sensing element.

Suppression of laser noise in CW 337μm HCN lasers

In a d.c.-discharge-excited 337 μm HCN laser, amplitude laser noise has been observed at the frequency range of 30 kHz to 1 MHz. The laser noise is classified into three types; oscillation noise having sharp peaks, broadly distributed noise having a center frequency and 1/ f-noise. Characteristics of the laser noise have been studied experimentally. The laser noise is caused by small oscillation which appears on d.c.-discharge current and by random fluctuations of current and plasma density. The laser noise has been suppressed more than 30 dB by adjusting the laser parameters such as discharge current, pressure and flow rates of mixed gas (CH4 4 + N 2 + He) and added He.

Subpicosecond laser timing stabilization

The 0.25 Hz-25 kHz pulse timing fluctuations of a Nd:YAG CW-mode-locked laser are reduced from 20.6 ps to less than 0.30 ps rms by an electronic phase-lock loop. Stabilizer design considerations include the laser phase control characteristics, phase detector additive noise, and spurious detection of the laser amplitude noise by the loop phase detector. Applications include synchronization of multiple picosecond pulsed lasers, and synchronization of lasers and electronic signal sources in picosecond physical measurements. >

High-frequency amplitude noise of stripe injection lasers

Measurements and a comparative analysis were made of the spectra of amplitude fluctuations of the radiation emitted by several types of cw injection laser at frequencies in the range 0.1–2.2 GHz.

A study of the ν1 fundamental and bend-excited hot band of DNN+ by velocity modulation absorption spectroscopy with an infrared difference frequency laser

The combined application of the ac discharge velocity modulation technique with cw tunable difference frequency infrared generation and dual beam subtraction of laser amplitude noise produces an extremely sensitive (10−6 absorbance/Hz1/2) direct absorption method for observing vibrational spectra of molecular ions. In this study we report observation of the fundamental ν1 (D–N stretch) of DNN+ in both P and R branches from J=0 to 24, as well as the 30-fold weaker hot band transitions originating from the (0110) bending state. l-doubling in these latter transitions is measured interferometrically with a precision of ±10 MHz. Spectroscopic constants for (0000), (1000), (0110), and (1110) states are reported and compared with ab initio calculations and previous microwave measurements for DNN+.

Modeling noise by jump processes in strong laser-atom interactions

In this paper, a practical scheme for computing time-dependent properties, such as excitation probabilities and dipole correlation functions of a multilevel atom strongly excited by a laser in the presence of noise, is described in detail. The method, which is based on the notion of randomly interrupted, multivalued jump processes, can be used to treat laser phase, amplitude, and/or frequency noise, and fluctuating microfields. The method provides analytic expressions, which are based on eigenvalues and eigenvectors of a finite-dimensional matrix, for time dependence and spectral dependence, and it permits computation of time-dependent fluorescence emitted from atoms excited by a noisy laser. The method is illustrated by application to time-dependent spectra.

Reduction of FM noise in impatt oscillators by optical illumination

Experiments are described in which laser illumination of the active device has reduced the FM noise output by up to 5 dB for a GaAs impatt oscillator and 2 dB for a Si impatt oscillator. A qualitative explanation of the observed results is given, and the effect of laser amplitude noise on the maximum noise reduction obtainable is shown.

Noise characteristics in line-narrowed semiconductor lasers with optical feedback

Effects of optical-feedback-induced line-narrowing on low-frequency amplitude and phase noise of semiconductor lasers are reported. Free-running laser noise is compared with that of lasers operating with external mirror feedback. While less than 1 dB difference in the amplitude noise with and without feedback is observed, line-narrowed lasers exhibit 15–20 dB reduction in low-frequency wavelength instability, or phase noise.

Laser noise in fiber-optic interferometer systems

The amplitude stability of single-mode channeled-substrate planar diode lasers has been measured as a function of frequency (100 Hz–1 MHz) and driving current. The relative noise spectrum showed a decrease with increasing frequency and an overall reduction at all frequencies as the output power of the laser was increased. These results are compared with similar measurements of the most stable commercial single-mode HeNe lasers. The problems of laser amplitude noise in fiber-optic sensor systems is briefly discussed.

Ultrafast laser scanner microscope.

Advances in monolayer deposition of cervical cells have removed one of the last serious obstacles to the design of high-resolution automated diagnostic assessment systems. In this article, we describe the design considerations for a system that is capable of acquiring, within 60 sec, a 0.5 micron digitized image of a 4 cm2 area on a standard glass slide. The most feasible approach is found to be a system using a rotating polygon to sweep the focused spot from a laser across a 2-mm scan line while the slide is uniformly translated perpendicular to the scan direction the use of laser sources (a helium-neon laser at 632 nm and a krypton ion laser at 568 and/or 476 nm) as compared to the incoherent light sources used in conventional microscope systems alleviates many of the optical design problems and provides the proper wavelengths needed for recognition of Papanicolaou stained cells. We also find that focus control of the scanning spot should be achievable using a technique involving a holographic grating. Other relevant considerations such as sample heating problems, multiphoton absorption by the sample, detector signal-to-noise ratios, laser amplitude noise control, and the digitization and buffering of the data stream are also discussed.