18 June 2015

FBH showcasing dual-wavelength diode laser for Raman spectroscopy

In hall B3 (booth 359) at Laser World of Photonics 2015 in Munich, Germany (22–25 June), FBH (Ferdinand-Braun-Institut, Leibniz-Institut fur Hoechstfrequenztechnik) of Berlin, Germany is showcasing a range of improvements and new developments regarding diode lasers and UV light-emitting diodes.

Separating signals – dual-wavelength diode laser for Raman spectroscopy

FBH is exhibiting novel dual-wavelength diode lasers suitable for use in miniaturized, portable laser measurement systems for Raman spectroscopy applications. The laser sources alternatingly emit light from only one chip at two different stabilized wavelengths, defined by gratings implemented into the chip. Wavelength selection is realized by separately addressable sections within the laser.

The diode laser chip is applicable for SERDS (shifted-excitation Raman difference spectroscopy), enabling the measurement of Raman spectra under real-world conditions even in highly fluorescent environments and when exposed to daylight. It is hence possible to separate Raman signals from background interference. Moreover, SERDS improves the detection limit by one order of magnitude compared with standard Raman spectroscopy.

Using such chip-scale monolithic light sources, a compact SERDS measurement head as small as a laser pointer has been realized for the first time, it is claimed. The device is the basis for a miniaturized and versatile SERDS spectroscopy system, enabling in-situ measurement in various security- and health-related fields including biology, medicine, food control, and pharmacy. Applications in absorption spectroscopy and terahertz radiation generation are also possible.

Higher brilliance and output power for diode lasers and bars

FBH develops high-brightness diode lasers in a variety of designs and packages, covering wavelengths of 630-1180nm. Single emitters with a stripe width of 90µm, for example, can reach 3.5W/mm-mrad (peak). The same applies to smaller stripes, delivering 4-5W/mm-mrad from a 30µm aperture.

For rapid prototyping applications, FBH has developed distributed Bragg reflector (DBR) ridge waveguide (RW) lasers with 24 individually addressable emitters featuring a wavelength spacing of >0.3nm and a spectral width of <1pm.

Further activities at FBH aim to constantly improve efficiency, reliability and output power. For example, bars emitting at a wavelength of around 940nm at temperatures of -70°C (203K) have yielded a record 2kW peak power per bar at a pulse width of 200µs. To date, such powers could only be achieved by combining the optical beams from at least four single bars, says FBH.

UV-B LED module for plant lighting

FBH is developing LED technology in the UV-B and UV-C spectral ranges, from the chip to the final radiation module. Applications are wide-ranging and include medical diagnostics and fluorescence spectroscopy as well as UV curing and disinfection.

A further application is plant lighting, for which the FBH has developed and manufactured a module enabling irradiation with UV-B light of a specific wavelength. In this particular case, LEDs emitting at a wavelength around 310nm are used to stimulate health-promoting secondary metabolites in plants. The optical power can be flexibly adjusted between 0 and 100%. The concept has been tested in experiments at the Institute of Vegetable and Ornamental Crops (IGZ). An exhibition module is available at FBH's Laser World of Photonics booth.

CLEO Europe

At the associated Conference on Lasers and Electro-Optics/Europe (CLEO Europe 2015), FBH is giving the short course 'High Power and High Brightness Semiconductor Laser Diodes and Applications'. It is also presenting several lectures and posters, including the following:

• narrowband gallium nitride (GaN) external-cavity diode laser with 400mW output power at 445nm for deep ultraviolet frequency doubling;

• micro-integrated, narrow-linewidth master oscillator power amplifier designed for quantum sensors in space;

• nanosecond high-current pulsed operation of ridge-waveguide lasers;

• coexistence of multiple stable continuous-wave states in micro-integrated external-cavity diode lasers;

• generation of 0.7W second-harmonic picosecond pulses near 560nm using a DBR diode laser and a ridge-waveguide PPLN crystal;

• GaAs-based phase modulator for laser radiation at 1070nm;

• coherent combining of two high-brightness laser diodes phase-locked by a Michelson-type external cavity;

• high-brightness narrow-stripe broad-area laser with 7W optical output at 910, 935 and 970nm for coarse spectral beam combining;

• timing jitter reduction of a two-section external-cavity semiconductor laser by harmonic mode-locking and optical feedback;

• spectral broadening of mode-locked semiconductor lasers by resonator-internal pulse shaping;

• controllable dual-wavelength-stabilized Y-branch DBR diode lasers at 785nm for SERDS;

• array with 24 DBR lasers for scanning applications (fabrication and characterization); and 

• increased slow-axis beam quality in 9xx nm high-power broad-area diode lasers by modifying the lateral current profile at the device edges.

Tags: Diode lasers

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