Concepts for High Power Laser Diode Systems 1. Introduction High power laser diode systems is a new development within the field of laser diode systems. Pioneer of such laser systems was SDL, Inc. which discontinued their product line in 1999. This technical document provides a summary of the different concepts and is designed to support customers in finding the best solution for their experimental requirements. The compared concepts include Master Laser Power Amplifier (MOPA) systems as well as tapered lasers with external cavity. Contents 1. Introduction... 1 2. Master Laser Power Amplifier (MOPA) Systems, DBR or DFB Master Laser... 2 3. Master Laser Power Amplifier (MOPA) Systems, Littrow Design... 3 4. Master Laser Power Amplifier (MOPA) Systems, Littrow Redesign... 4 5. Master Laser Power Amplifier (MOPA) Systems, Littman/Metcalf Design... 5 6. Master Laser Power Amplifier (MOPA) Systems, Littman/Metcalf Redesign... 6 7. Tapered Laser with External Cavity in Littrow Configuration... 7 8. Tapered Laser with External Cavity in Littman/Metcalf Configuration... 8 9. Summary and Comparison of the Different Concepts... 9 10. Literature... 10 Document: http://data.sacher-laser.com/techdocs/mopa.pdf. Page 1
2. Master Laser Power Amplifier (MOPA) Systems, DBR or DFB Master Laser The Master Laser Power Amplifier (MOPA) system is well known from literature since several years. It is able to achieve optical powers up to 2.5 Watt at 780nm. Tapered Amplifier Grating Laser 60dB OI Figure 2: Schematic setup of a MOPA system with a master Figure 2 shows the setup of a MOPA system with a master laser. As master laser DFB, DBR as external cavity laser are suitable. The beam of the master laser is coupled out via back facet of the laser diode. Master laser and the tapered amplifier are decoupled via a 60dB optical isolator. The alignment of the beam relative to the 3µm x 1µm aperture of the tapered amplifier is performed via two alignment mirrors. The tapered amplifier performs an optical amplification of typically 15mW 30mW up to the nominal output power of the MOPA system. The output beam of the tapered amplifier is collimated via two stage collimation optics. The tapered amplifier itself is protected via a 35dB optical isolator. 60dB isolators are available upon request. Spectral properties of the complete MOPA system are mainly determined by the spectral properties of the master laser. This results in typical linewidth of 1MHz (50ms), 5MHz (20s). The side-mode suppression is in the order of 55dB. between 500mW and 1500mW. Mechanical stability is determined by the stability of the adjustment mirrors. Advantage of this configuration is that there are no moving parts within the alignment sensitive beam path between master laser and power amplifier. Document: http://data.sacher-laser.com/techdocs/mopa.pdf. Page 2
3. Master Laser Power Amplifier (MOPA) Systems, Littrow Design The Master Laser Power Amplifier (MOPA) system is well known from literature since several years. It is able to achieve optical powers up to 2.5 Watt at 780nm. Tapered Amplifier Beam Steering Mirror 60dB OI Laser Grating Figure 1: Schematic setup of a MOPA system with a master laser in Littrow design Figure 1 shows the most common setup of a MOPA system with a master laser in Littrow configuration. The beam of the Littrow master laser is coupled out via the 0 th order of the diffraction grating. The beam steering is corrected via a beam steering mirror, c/f http://data.sacher.us/techdocs/bcm.pdf. Master laser and the tapered amplifier are decoupled via a 60dB optical isolator. The alignment of the beam relative to the 3µm x 1µm aperture of the tapered amplifier is performed via two alignment mirrors. The tapered amplifier performs an optical amplification of typically 15mW 30mW up to nominal output power of the MOPA system. The output beam of the tapered amplifier is collimated via two stage collimation optics. The tapered amplifier itself is protected via a 35dB optical isolator. 60dB isolators are available upon request. Spectral properties of the complete MOPA system are mainly determined by the spectral properties of the master laser. This results in typical linewidth of 1MHz (50ms), 5MHz (20s). The side-mode suppression is in the order of 40dB. between 500mW and 1500mW. Mechanical stability is determined by the stability of the adjustment mirrors as well as by the beam steering mirror. The beam steering mirror causes a parallel shift of the master laser beam during the wavelength scan. The absolute values of this beam shift is approximately ½ of the length change of the piezo actuator (up to 1-2µm) which results in a 0.5-1µm parallel shift of the laser beam. This value relates to the 1.5µm x 0.5µm adjustment tolerance for best coupling into the tapered amplifier. Document: http://data.sacher-laser.com/techdocs/mopa.pdf. Page 3
4. Master Laser Power Amplifier (MOPA) Systems, Littrow Redesign The Master Laser Power Amplifier (MOPA) system is well known from literature since several years. has realized this design with using their redesigned Littrow laser system as master laser. Tapered Amplifier Grating Laser 60dB OI Figure 2: Schematic setup of a MOPA system with a master laser in Littrow design Figure 2 shows the setup of a MOPA system with a master laser in Littrow configuration without the need for the beam steering mirror. The beam of the Littrow master laser is coupled out via back facet of the laser diode. Master laser and the tapered amplifier are decoupled via a 60dB optical isolator. The alignment of the beam relative to the 3µm x 1µm aperture of the tapered amplifier is performed via two alignment mirrors. The tapered amplifier performs an optical amplification of typically 15mW 30mW up to the nominal output power of the MOPA system. The output beam of the tapered amplifier is collimated via two stage collimation optics. The tapered amplifier itself is protected via a 35dB optical isolator. 60dB isolators are available upon request. Spectral properties of the complete MOPA system are mainly determined by the spectral properties of the master laser. This results in typical linewidth of 1MHz (50ms), 5MHz (20s). The side-mode suppression is in the order of 55dB. between 500mW and 1500mW. Mechanical stability is determined by the stability of the adjustment mirrors. Advantage of this configuration is that there are no moving parts within the alignment sensitive beam path between master laser and power amplifier. Document: http://data.sacher-laser.com/techdocs/mopa.pdf. Page 4
5. Master Laser Power Amplifier (MOPA) Systems, Littman/Metcalf Design The Master Laser Power Amplifier (MOPA) system is well known from literature since several years. has realized this design with using a Littman/Metcalf laser system as master laser. Tapered Amplifier Tuning Mirror Laser Grating 60dB OI Figure 3: Schematic setup of a MOPA system with a master laser in Littrow design Figure 3 shows the setup of a MOPA system with a master laser in Littman/Metcalf configuration. The beam of the Littman/Metcalf master laser is coupled out via back facet of the laser diode. Master laser and the tapered amplifier are decoupled via a 60dB optical isolator. The alignment of the beam relative to the 3µm x 1µm aperture of the tapered amplifier is performed via two alignment mirrors. The tapered amplifier performs an optical amplification of typically 15mW 30mW up to the nominal power values of the MOPA system. The output beam of the tapered amplifier is collimated via two stage collimation optics. The tapered amplifier itself is protected via a 35dB optical isolator. 60dB isolators are available upon request. Spectral properties of the complete MOPA system are mainly determined by the spectral properties of the master laser. This results in typical linewidth of 500kHz (50ms), 2MHz (20s). The side-mode suppression is in the order of 40dB. between 500mW and 1500mW. Mechanical stability is determined by the stability of the adjustment mirrors. Advantage of this configuration is that there are no moving parts within the alignment sensitive beam path between master laser and power amplifier. The patented alignment insensitive Littman/Metcalf cavity design results in a turn-key system. Mode-hop free tuning range is improved in comparison to the Littrow configuration due to our patented Littman/Metcalf cavity design. This results in a much easier handling of the MOPA system. Document: http://data.sacher-laser.com/techdocs/mopa.pdf. Page 5
6. Master Laser Power Amplifier (MOPA) Systems, Littman/Metcalf Redesign The Master Laser Power Amplifier (MOPA) system is well known from literature since several years. has modified this design with using their redesigned Littman/Metcalf laser system as master laser. Tapered Amplifier Laser 60dB OI Figure 4: Schematic setup of a MOPA system with a master laser in Littrow design Figure 4 shows the setup of a MOPA system with a master laser in Littman/Metcalf configuration. The beam of the Littman/Metcalf master laser is coupled out via back facet of the laser diode. Master laser and the tapered amplifier are decoupled via a 60dB optical isolator. The alignment of the beam relative to the 3µm x 1µm aperture of the tapered amplifier is performed via two alignment mirrors. The tapered amplifier performs an optical amplification of typically 15mW 30mW up to the nominal power values of the MOPA system. The output beam of the tapered amplifier is collimated via two stage collimation optics. The tapered amplifier itself is protected via a 35dB optical isolator. 60dB isolators are available upon request. Spectral properties of the complete MOPA system are mainly determined by the spectral properties of the master laser. This results in typical linewidth of 500kHz (50ms), 2MHz (20s). The side-mode suppression is in the order of 55dB. between 500mW and 1500mW. Mechanical stability is determined by the stability of the adjustment mirrors. Advantage of this configuration is that there are no moving parts within the alignment sensitive beam path between master laser and power amplifier. The patented alignment insensitive Littman/Metcalf cavity design results in a turn-key system. Mode-hop free tuning range is improved in comparison to the Littrow configuration due to our patented Littman/Metcalf cavity design. This results in a much easier handling of the MOPA system. Document: http://data.sacher-laser.com/techdocs/mopa.pdf. Page 6
7. Tapered Laser with External Cavity in Littrow Configuration This concept is an alternative to the well known Master Laser Power Amplifier (MOPA) concept. developed this concept since in 2001. It was commercialized since late 2002. Since then, more than three international conference contributions, publications and patent applications have been published on the properties and the performance of this system in MOT applications. Please find downloadable copies at http://www.sacher-laser.com/pubdocs2.php from our website. Tapered Laser Grating Figure 5: Schematic setup of a tapered laser system in Littrow design Figure 5 shows the setup of a tapered laser in Littrow configuration. The frequency generation as well as the power amplification are unified in one single stage device. Available power values are in the order of 500mW 1000mW, depending on the wavelength. The output beam of the tapered laser is collimated via two stage collimation optics. The tapered laser itself is protected via a 35dB optical isolator. 60dB isolators are available upon request. Spectral properties of the complete tapered laser system are determined by the performance of the external cavity. This results in typical linewidth of 1MHz (50ms), 10MHz (20s). The sidemode suppression is in the order of 55dB. between 500mW and 1000mW. Mechanical stability is determined by the stability of the external cavity. It is determined by the robust flex design without any moving parts. This concept has been proven to fully replace expensive MOPA systems. Document: http://data.sacher-laser.com/techdocs/mopa.pdf. Page 7
8. Tapered Laser with External Cavity in Littman/Metcalf Configuration This concept is an alternative to the well known Master Laser Power Amplifier (MOPA) concept. developed and commercialized this concept since 2004. It benefits from more than 10 years of experience of in manufacturing tunable diode laser systems in Littman/Metcalf configuration. Tapered Laser Grating Figure 6: Schematic setup of a tapered laser system in Littman/Metcalf design Figure 6 shows the setup of a tapered laser in Littman/Metcalf configuration. The frequency generation as well as the power amplification are unified in one single stage device. Available power values are in the order of 500mW 1000mW, depending on the wavelength. The output beam of the tapered laser is collimated via two stage collimation optics. The tapered laser itself is protected via a 35dB optical isolator. 60dB isolators are available upon request. Spectral properties of the complete tapered laser system are determined by the performance of the external cavity. This results in typical linewidth of 500kHz (50ms), 5MHz (20s). The side-mode suppression is in the order of 55dB. between 500mW and 1000mW. Mechanical stability is determined by the stability of the external cavity. It is determined by the patented alignment insensitive Littman/Metcalf cavity design. Mode-hop free tuning range is improved in comparison to the Littrow configuration due to our patented Littman/Metcalf cavity design. This results in a much easier handling of the tapered laser system.. Document: http://data.sacher-laser.com/techdocs/mopa.pdf. Page 8
9. Summary and Comparison of the Different Concepts This document provides a brief description of different concepts for high power laser diode system. In total, we presented 6 different concepts with different physical properties and different physical behavior. The following concepts have been presented and discussed: MOPA System with Master Laser in Littrow Configuration: This configuration is well known from literature. Most of the current work is still performed with this concept. It is a robust laboratory instrument which requires technically skilled scientists for operation. MOPA System with Master Laser in New Littrow Configuration: This concept is a modification of the original Littrow-MOPA. It results in an easier handling of the complete system and requires less time for getting started up. It is a robust laboratory instrument for scientists. MOPA System with Master Laser in Littman/Metcalf Configuration: This concept is a development which avoids the drawbacks of the original Littrow-MOPA. It results in a turn-key laser system which is easy to be handled. It is a robust laboratory instrument for scientists. MOPA System with Master Laser in New Littman/Metcalf Configuration: This concept is a development which avoids the drawbacks of the original Littrow-MOPA. It results in a turn-key laser system which is easy to be handled. It is a robust laboratory instrument for scientists and has the option for being motorized. Tapered Laser in Littrow Configuration: This concept was started for providing a cost effective solution for high power diode laser systems. Most current high power tunable diode laser systems in the 780nm regime are currently sold with this concept. It is a turn-key laser system. Tapered Laser in Littman/Metcalf Configuration: This concept bases in the Tapered Laser in Littrow Configuration. Advantages are the higher modehop free tuning range and the option for motorizing this laser system for automated measuring setups. It is a turn-key laser system. Document: http://data.sacher-laser.com/techdocs/mopa.pdf. Page 9
10. Literature [1] S. Stry, R. Knispel, L. Hildebrandt, J. Sacher, Compact Tuneable Diode Laser with Diffraction Limited 500 mw and their application in BEC and CDRS, TDLS, Zermatt, July 2003 [2] S. Stry, L. Hildebrandt, J. Sacher, C. Buggle, M. Kemmann, W. von Klitzing, Compact tunable diode laser with diffraction limited 1W for atom cooling and trapping, Photonics West 2004 [3] S. Stry, L. Hildebrandt, J. Sacher, Compact Tunable External Cavity Diode Laser with Diffraction Limited 1Watt optical power, and their application in BEC and CRDS, Photonics Europe 2004 [4] (to be continued) Document: http://data.sacher-laser.com/techdocs/mopa.pdf. Page 10