rus
Issue #1/2016
M.Bogdanovich, A.Grigor’ev, K.Lantsov, K.Lepchenkov, A.Ryabtsev, G.Ryabtsev, U.Tsitavets, M.Shchemelev
Portable Diode-Pumped Solid-State Lasers
Portable Diode-Pumped Solid-State Lasers
Compact and light laser devices emitting in the spectral range of 1.5–1.6 µm and characterized by very low power/energy consumption are indispensible for small-size range finders, target illumination and tracking systems, portable medical apparatus.
Diode–pumped solid-state lasers (DPSSLs) are characterized by low power consumption levels, compact dimensions and small weight in contrast with flash lamp pumped light emitters with similar output parameters. In most cases the lifetime of laser diode arrays (LDAs) and laser diode bars (LDBs) used as the pump radiation sources are two or even more orders of magnitude greater than that for the flash lamps. As a result nowadays DPSSLs are practically exclusive radiation sources for rangefinders, target illumination and/or tracking systems, spectroscopy, medicine, space researches and also for a number of special technological applications.
An extensive work on research, development and manufacturing in the field of laser physics and technique is performed at the B.I. Stepanov Institute of Physics of National Academy of Sciences of Belarus (NASB). Parameters of laser diode arrays and bars are studied in extreme environmental and operational conditions, their characteristics are optimized for effective application within the diode pump units. Much attention is given to investigations devoted to increase of the output energy and beam quality of DPSSLs and their operation lifetime. With this in mind, modeling of electrical, optical and thermal processes responsible for operation of the entire laser and its individual units under conditions similar to real regimes of applications are realized.
There are four main directions of works performed at the Institute of Physics of NASB and related to the development and manufacturing of prototypes and serial diode-pumped lasers: 1) ytterbium–erbium lasers operating within the eye–safe spectral region (1.5–1.6 мкм), 2) DPSSLs based on Nd 3–containing active elements (AE) with air cooling (radiation pulse repetition rate up to 100 Hz), 3) DPSSLs based on Nd 3+–containing active elements with water cooling (radiation pulse repetition rate up to 1 kHz), 4) optical parametric oscillators (OPOs) emitting within the spectral regions 1.5–1.6 and 3.0–5.0 µm. The laser diode modules based on (In, Al) GaAs/AlGaAs heterostructures capable of generating the light fluxes with high pulse power/energy in the spectral intervals 0.94–0.96 and 0.80–0.82 µm are used as pump radiation sources. As a rule, DPSSLs created at the Institute of Physics of NASB are supplied with the diode pump units operating in accordance with the transversal scheme of delivery of radiation. However, in some cases (e. g., when the technological picosecond laser or the laser with the extremely narrow lasing line width for Doppler lidar were developed) the longitudinal version of AE excitation is applied. It should be noted that all optical components including dielectric mirrors, polarizers and so on which are normally used in experimental studies and installed into serial laser samples are manufactured in Optical department of the Institute of Physics of NASB.
For modern small–sized range finders, optoelectronic target illumination and tracking systems, potable medicine devices as well as for laser spectroscopy and laser cleaning facilities the compact and light lasers emitting in the spectral range 1.5–1.6 µm and characterized by very low power/energy consumption are required. For this purpose the set of LDA–pumped ytterbium–erbium lasers (Fig. 1) operating in the passive or electro–optical Q–switched mode has been developed at the Institute of Physics of NASB. The developed lasers allow obtaining the nanosecond radiation pulses with the energy up to 10 mJ and the repetition rates up to 10 Hz. Construction of the ytterbium–erbium lasers ensures functioning of the devices at the fundamental transversal ТЕМ00 mode with the output beam quality parameter М2 < 1.5 for a wide ambient temperature range from minus 50 till plus 55 Celsius degrees. The power consumption for the ytterbium–erbium lasers is less than 20 W at the pulse repetition rate of 5 Hz throughout all operation temperature range.
Developments of optical parametric oscillators based on the LDB–pumped Nd: YAG master lasers are directed on solving the problem of an enhancement of laser beam energy up to the levels of 15–50 mJ with increasing the radiation pulse repetition rate up to 30–60 Hz within the eye–safe spectral range 1.5–1.6 µm. This activity is important for a number of modern optoelectronic devices used in various applied spheres. Such OPO systems must have extremely small weight and dimensions, theirs power consumption must be no more than 200 W. Simultaneously, the OPO emitters must be characterized by high temporal stability and low value of the output beam quality parameter М2. Optical parametric oscillators developed at the Institute of Physics of NASB have forced air or conductive (through the OPO base) cooling units. Appearance of the head part of one version of OPO (IFL-N5030/N2560-OPO) satisfying to the above–mentioned requirements along with the distribution of a radiation intensity in the OPO output beam cross–section are given in Fig. 2.
The majority of diode–pumped solid-state lasers with the radiation pulse repetition rate up to 1 kHz developed and created at the Institute of Physics of NASB using the crystals and glasses containing neodymium ions are based on application of the quantrons (laser head) with improved power/energy and spatial characteristics [1]. The convective cooled (without usage of cooling liquids) quantrons with AEs which side surfaces are covered by the patent scattering layer [2] were well established in the composition of the Nd: YAG Q–switched DPSSLs excited up to the output beam energy of 200 mJ using the transversal LDB–pumped scheme.
For application to the spectroscopic complexes the version of compact air cooled Nd:YAG laser (IFL-N315-UV) generating the fourth harmonic (0.266 мкм) of the fundamental mode frequency. The lasing output pulse duration is less than 8 ns at the pulse repetition rate of 15 Hz and output energy of 3 mJ. The laser head and power supply unit designated for a voltage of 10VDC are integrated in one housing with dimensions of 100 Ч 200 Ч 350 mm.
Some application areas require the compact more powerful (more than 200 mJ) lasers which do not use water cooling. In this cases the laser optical schemes with amplification stages are implemented. As an example, the laser emitter with the output energy up to 400 mJ capable of operating simultaneously at three wavelengths 1.064, 0.532 and 0.355 µm while maintaining the high output beam quality (М2 < 6) for a mobile lidar [3] is presented in Fig. 3. Today the testing procedures for the LDB–pumped air cooled Nd: YAG optical system emitting the radiation pulses with the energy up to 800 mJ (the wavelength 1.064 µm) have been completed at the Institute of Physics of NASB. As in the case of ytterbium–erbium lasers the emitters on the base of Nd: YAG active elements are characterized by a relatively low energy consumption level (approximately 200–300 W in the regime of lasing with the radiation pulse repetition rate of 10 Hz and output energy of 400 mJ) and small dimensions.
For modern picosecond and/or femtosecond forming systems as well as for the material treatment complexes the neodymium lasers with the output radiation pulse repetition rate of 500–1000 Hz are required. For these purposes the Nd: YAG Q–switched water cooled (closed type) DPSSL allows emitting the laser pulses with the energies about 50 mJ at the pulse repetition rate up to 1 kHz is in the development. Experimental example of such laser device has been successfully passed the set of parameter measurement and endurance tests. At this stage the emitter prototype is under preparation.
An extensive work on research, development and manufacturing in the field of laser physics and technique is performed at the B.I. Stepanov Institute of Physics of National Academy of Sciences of Belarus (NASB). Parameters of laser diode arrays and bars are studied in extreme environmental and operational conditions, their characteristics are optimized for effective application within the diode pump units. Much attention is given to investigations devoted to increase of the output energy and beam quality of DPSSLs and their operation lifetime. With this in mind, modeling of electrical, optical and thermal processes responsible for operation of the entire laser and its individual units under conditions similar to real regimes of applications are realized.
There are four main directions of works performed at the Institute of Physics of NASB and related to the development and manufacturing of prototypes and serial diode-pumped lasers: 1) ytterbium–erbium lasers operating within the eye–safe spectral region (1.5–1.6 мкм), 2) DPSSLs based on Nd 3–containing active elements (AE) with air cooling (radiation pulse repetition rate up to 100 Hz), 3) DPSSLs based on Nd 3+–containing active elements with water cooling (radiation pulse repetition rate up to 1 kHz), 4) optical parametric oscillators (OPOs) emitting within the spectral regions 1.5–1.6 and 3.0–5.0 µm. The laser diode modules based on (In, Al) GaAs/AlGaAs heterostructures capable of generating the light fluxes with high pulse power/energy in the spectral intervals 0.94–0.96 and 0.80–0.82 µm are used as pump radiation sources. As a rule, DPSSLs created at the Institute of Physics of NASB are supplied with the diode pump units operating in accordance with the transversal scheme of delivery of radiation. However, in some cases (e. g., when the technological picosecond laser or the laser with the extremely narrow lasing line width for Doppler lidar were developed) the longitudinal version of AE excitation is applied. It should be noted that all optical components including dielectric mirrors, polarizers and so on which are normally used in experimental studies and installed into serial laser samples are manufactured in Optical department of the Institute of Physics of NASB.
For modern small–sized range finders, optoelectronic target illumination and tracking systems, potable medicine devices as well as for laser spectroscopy and laser cleaning facilities the compact and light lasers emitting in the spectral range 1.5–1.6 µm and characterized by very low power/energy consumption are required. For this purpose the set of LDA–pumped ytterbium–erbium lasers (Fig. 1) operating in the passive or electro–optical Q–switched mode has been developed at the Institute of Physics of NASB. The developed lasers allow obtaining the nanosecond radiation pulses with the energy up to 10 mJ and the repetition rates up to 10 Hz. Construction of the ytterbium–erbium lasers ensures functioning of the devices at the fundamental transversal ТЕМ00 mode with the output beam quality parameter М2 < 1.5 for a wide ambient temperature range from minus 50 till plus 55 Celsius degrees. The power consumption for the ytterbium–erbium lasers is less than 20 W at the pulse repetition rate of 5 Hz throughout all operation temperature range.
Developments of optical parametric oscillators based on the LDB–pumped Nd: YAG master lasers are directed on solving the problem of an enhancement of laser beam energy up to the levels of 15–50 mJ with increasing the radiation pulse repetition rate up to 30–60 Hz within the eye–safe spectral range 1.5–1.6 µm. This activity is important for a number of modern optoelectronic devices used in various applied spheres. Such OPO systems must have extremely small weight and dimensions, theirs power consumption must be no more than 200 W. Simultaneously, the OPO emitters must be characterized by high temporal stability and low value of the output beam quality parameter М2. Optical parametric oscillators developed at the Institute of Physics of NASB have forced air or conductive (through the OPO base) cooling units. Appearance of the head part of one version of OPO (IFL-N5030/N2560-OPO) satisfying to the above–mentioned requirements along with the distribution of a radiation intensity in the OPO output beam cross–section are given in Fig. 2.
The majority of diode–pumped solid-state lasers with the radiation pulse repetition rate up to 1 kHz developed and created at the Institute of Physics of NASB using the crystals and glasses containing neodymium ions are based on application of the quantrons (laser head) with improved power/energy and spatial characteristics [1]. The convective cooled (without usage of cooling liquids) quantrons with AEs which side surfaces are covered by the patent scattering layer [2] were well established in the composition of the Nd: YAG Q–switched DPSSLs excited up to the output beam energy of 200 mJ using the transversal LDB–pumped scheme.
For application to the spectroscopic complexes the version of compact air cooled Nd:YAG laser (IFL-N315-UV) generating the fourth harmonic (0.266 мкм) of the fundamental mode frequency. The lasing output pulse duration is less than 8 ns at the pulse repetition rate of 15 Hz and output energy of 3 mJ. The laser head and power supply unit designated for a voltage of 10VDC are integrated in one housing with dimensions of 100 Ч 200 Ч 350 mm.
Some application areas require the compact more powerful (more than 200 mJ) lasers which do not use water cooling. In this cases the laser optical schemes with amplification stages are implemented. As an example, the laser emitter with the output energy up to 400 mJ capable of operating simultaneously at three wavelengths 1.064, 0.532 and 0.355 µm while maintaining the high output beam quality (М2 < 6) for a mobile lidar [3] is presented in Fig. 3. Today the testing procedures for the LDB–pumped air cooled Nd: YAG optical system emitting the radiation pulses with the energy up to 800 mJ (the wavelength 1.064 µm) have been completed at the Institute of Physics of NASB. As in the case of ytterbium–erbium lasers the emitters on the base of Nd: YAG active elements are characterized by a relatively low energy consumption level (approximately 200–300 W in the regime of lasing with the radiation pulse repetition rate of 10 Hz and output energy of 400 mJ) and small dimensions.
For modern picosecond and/or femtosecond forming systems as well as for the material treatment complexes the neodymium lasers with the output radiation pulse repetition rate of 500–1000 Hz are required. For these purposes the Nd: YAG Q–switched water cooled (closed type) DPSSL allows emitting the laser pulses with the energies about 50 mJ at the pulse repetition rate up to 1 kHz is in the development. Experimental example of such laser device has been successfully passed the set of parameter measurement and endurance tests. At this stage the emitter prototype is under preparation.
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