Lei S. Meng

High power 7-GHz bandwidth external-cavity diode laser array and its use in optically pumping singlet delta oxygen

Spectral bandwidth of a diode laser array is narrowed to 7 GHz FWHM by using a thick volume Bragg grating. Total output power reaches 13.5 W cw, of which 86% is in the 7-GHz band.

Continuous-wave rotational Raman laser in H 2

A diode-pumped, far-off-resonance cw Raman laser in H(2) with rotational Stokes emission is reported for the first time to our knowledge. The Raman laser can produce single-wavelength emission at either 830 nm (rotational Stokes) or 1180 nm (vibrational Stokes) depending on the frequency tuning of the pump laser. The mirrors for the rotational cw Raman laser are easier to produce; the laser also exhibits a wider continuous tuning range and is less sensitive to thermal effects than the previously studied vibrational Raman laser [Opt. Lett. 26, 426 (2001) and references therein].

High-conversion-efficiency, diode-pumped continuous-wave Raman laser

We demonstrate a diode-pumped cw Raman laser in H(2) with photon-conversion efficiency of (66+/-8)%. Pumped by an injection-locked diode laser at 792 nm, the Stokes laser produces a peak output power of ~16mW at 1180 nm. Accompanying the high Stokes power are deviations from the existing theory, which are believed to be caused by the thermal-lensing effect of the Raman gas.

85% power conversion efficiency 975-nm broad area diode lasers at − 50°C, 76 % at 10°C

Optimized single stripe 975-nm broad area devices deliver 76% power conversion efficiency at 10degC. Cooling the material leads to 85% efficiency at -50degC. External differential quantum efficiency is the dominant term.

Amplified output of a frequency chirped diode source via injection locking

Injection locking is a useful technique for amplifying the output power of a tunable external cavity diode laser. The injection-locked output retains the spectral properties of the injected signal while offering high powers. A self-aligning injection-locked system is demonstrated that uses a chirped external cavity diode laser as the master laser. A gain of 51.8 dB is demonstrated with injection-locked output powers greater than 62 mW The amplified linear frequency chirp of 800 MHz in 4 ?s is measured and shows no deviation from the frequency chirp of the master laser. The high gain and ability of the injection-locked output to follow the rapid tuning of the injected source make it an excellent amplification technique for applications requiring higher powers with fast tuning.

2.3-kW continuous operation cryogenic Yb:YAG laser

We present our recent developments in high-power, high-efficiency cryogenic Yb:YAG laser systems. Specifically, we will discuss our 2.3-kW master oscillator power amplifier (MOPA) which has shown optical wall-plug efficiencies above 30-% (diode-driver input to optical output). This laser system has been operated for long run times with continuous wave and pulsed output formats. The beam quality factor, M2, of the MOPA has been measured to be less than 2 and it is currently limited by the master oscillator. We are working to improve the devices beam quality and output power. In addition, we have demonstrated an all-cryogenic Yb:YAG laser that produced 29 W of optical power. Use of cryogenic diode laser pumps represents our next step towards achieving greater than 50% efficient high-power laser systems.

Using an injection-locked diode laser to pump a CW Raman laser

We demonstrate the use of an injection-locked diode laser (792 nm) as the pump source for a continuous-wave (CW) Raman laser with Stokes emission at 1182 nm. Phase modulation of the master signal is imparted to the slave laser output in order to generate an error signal for phase/frequency locking via the Pound-Drever-Hall method. To illustrate the utility of this technique, we achieve the highest pump rate yet observed for a CW Raman laser (>90 times threshold) and compare the data to the existing theory. We also show how current modulation of the slave laser can eliminate the need for an electrooptic modulator in the system altogether.

Diode laser transmitter for water vapor DIAL measurements

The design and performance of two diode laser based transmitters for differential absorption LIDAR (DIAL) are presented. The first laser transmitter uses a tunable external cavity diode laser (ECDL) in the Littman-Metcalf cavity configuration to injection seed a flared amplifier. Water vapor absorption measurements are demonstrated with this laser transmitter operating in a continuous wave mode. The second diode based laser transmitter uses an ECDL in the Littrow cavity configuration and angle-angle semiconductor optical amplifiers to produce amplified laser pulses. Both designs are easily adaptable to wavelengths in the visible to the near infrared spectral region.

Progress toward a water-vapor differential absorption lidar (DIAL) using a widely tunable amplified diode laser source

Water vapor is one of the most significant constituents of the atmosphere because of its role in cloud formation, precipitation, and interactions with electromagnetic radiation, especially its absorption of longwave infrared radiation. Some details of the role of water vapor and related feedback mechanisms in the Earth system need to be characterized better if local weather, global climate, and the water cycle are to be understood. A Differential Absorption LIDAR (DIAL) with a compact laser diode source may be able to provide boundary-layer water vapor profiles with improved vertical resolution relative to passive remote sensors. While the tradeoff with small DIAL systems is lower vertical resolution relative to large LIDARs, the advantage is that DIAL systems can be built much smaller and more robust at less cost, and consequently are the more ideal choice for creating a multi-point array or satellite-borne system. This paper highlights the progress made at Montana State University towards a water vapor DIAL using a widely tunable amplified external cavity diode laser (ECDL) transmitter. The ECDL is configured in a Littman-Metcalf configuration and was built at Montana State University. It has a continuous wave (cw) output power of 20 mW, a center wavelength of 832 nm, a coarse tuning range of 17 nm, and a continuous tuning range greater than 20 GHz. The ECDL is used to injection seed a tapered amplifier with a cw output power of 500 mW. The spectral characteristics of the ECDL are transferred to the output of the tapered amplifier. The rest of the LIDAR uses commercially available telescopes, filter optics, and detectors. Initial cw and pulsed absorption measurements are presented.

High-efficiency continuous-wave Raman laser pumped by an injection-locked broad-area diode laser

We report an efficient CW far-off-resonance Raman laser in H/sub 2/ gas pumped by an injection-locked broad-area diode laser. The pump wavelength 794 nm is Raman shifted to the Stokes wavelength 1185 nm. The total output Stokes power reaches 21.6/spl plusmn/0.5 mW and the photon conversion efficiency reaches (74/spl plusmn/10)%.