High-efficiency 1064 nm nonplanar ring oscillator Nd:YAG laser with diode pumping at 885 nm.

We experimentally demonstrate a monolithic single-frequency nonplanar ring oscillator (NPRO) laser pumped by diode lasers from a thermally excited ground level directly into a metastable level of Nd3+:YAG gain medium. Continuous-wave output power of 4.54 W is obtained at 1064 nm with 7.6 W input at 885 nm, and the slope efficiency is 76.9% at incident power above 2 W. Compared with the 50.7% slope efficiency obtained using 808 nm pumping for the same NPRO, this direct pumping shows a potential advantage in improving the energy efficiency. The observation is consistent with an analysis of the heat generation in both direct and traditional pumping schemes. The power fluctuation is measured to be within 0.8% at 3 W output during a 10 h period.

Temporal response of laser power standards with natural convective cooling.

Laser power detectors with natural convective cooling are convenient to use and hence widely applicable in a power range below 150 W. However, the temporal response characteristics of the laser power detectors need to be studied in detail for accurate measurement. The temporal response based on the absolute laser power standards with natural convective cooling is studied through theoretical analysis, numerical simulations, and experimental verifications. Our results show that the response deviates from a single exponential function and that an ultimate response balance is difficult to achieve because the temperature rise of the heat sink leads to continuous increase of the response. To determine the measurement values, an equal time reading method is proposed and validated by the laser power calibrations.

Improvement of measurement uncertainties in laser power detector calibration by convolving with the detector's impulse response function.

For the calibration of thermal type laser power detectors with slow response time, instability of the input laser significantly contributes to the measurement repeatability. A convolution method is adopted to reduce the impact of source instability. The equivalent incident power is calculated by convolving the real-time power input and the detector impulse-response function (IRF). The value is applied in place of the traditional input power value for the calibration. The IRF is measured using the (1-70) W laser power primary standard at National Institute of Metrology of China. The measurement repeatability of the transfer detector's responsivity is improved from 1.1% using the traditional method to 0.19% using this method. The systematic errors, primarily due to source drift are also reduced. The proposed method can be applied in the calibration of general thermal type laser power detectors.

High-finesse cavity external optical feedback DFB laser with hertz relative linewidth.

We report hertz level relative linewidth distributed feedback diode lasers with external optical feedback from a high finesse F-P cavity, and demonstrate the efficient phase noise suppression and laser linewidth reduction of the optical feedback technique. The laser phase noise is dramatically suppressed throughout the measurement frequency range. Especially at the Fourier frequency of 17 kHz, approximately the linewidth of the F-P reference cavity, the laser phase noise is significantly suppressed by more than 92 dB. Above this Fourier frequency, the noise maintains a white phase noise plateau as low as -124.4 dBc/Hz. The laser's FWHM linewidth is reduced from 7 MHz to 4.4 Hz, and its instantaneous linewidth is 220 mHz in the Lorentzian fitting.

External cavity diode laser with kilohertz linewidth by a monolithic folded Fabry-Perot cavity optical feedback.

We present a extended-cavity diode laser (ECDL) with kilohertz linewidth by optical feedback from a monolithic folded Fabry-Perot cavity (MFC). In our experiments, an MFC replaces the retroreflecting mirror in the traditional ECDL configuration. Beat-note measurements between this MFC-ECDL and a narrow-linewidth reference laser are performed and demonstrate that the linewidth of this MFC-ECDL is about 6.8 kHz. Phase locking of this MFC-ECDL to the reference laser is achieved with a unity gain as small as 10.2 kHz.

Quasi synchronous tuning for grating feedback lasers.

A general analytical form of the round trip phase shift in grating feedback diode lasers is proposed. Using the new form, it is obvious that the round trip phase shift can be independent of rotation angle in first order approximation when only one restriction condition is met. We call this the quasi synchronous tuning (QST) condition. In the QST region, a considerably large mode hopping free tuning range can be obtained. An adjustment structure with only one freedom is needed to accurately find and locate the quasi synchronous pivot, which is not strictly confined on the grating surface and its extension. It means that the external cavity diode lasers design can be easier and the laser can be more stable and reliable.

[Studies on the hyperfine structures of I2 absorption line with third harmonic frequency stabilization in Nd:YVO4-KTP ring laser].

The experiment for research on the hyperfine structure of I2 absorption lines with third harmonic frequency stabilization in Nd: YVO4-KTP ring laser has been done. The hyperfine structures of two lines have been observed and the results are comparable with the theoretical calculations. One of the two lines is R(70) 36-1 is the transition of the excited state.